The University of Iowa Center for Credit Programs Distance Education Study Guide for 027:053 Human Anatomy College of Liberal Arts and Sciences Integrative Physiology Course Prepared by Kenneth E. Mobily, Ph.D. 3 Semester Hours 8 Written Assignments 4 Examinations
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The University of Iowa
Center for Credit Programs
Distance Education Study Guide
for
027:053 Human Anatomy
College of Liberal Arts and Sciences Integrative Physiology
No part of this publication may be reproduced in any form by any means
without permission in writing from the publisher.
r 1/95 r 4/98 r 3/02 r 7/05 r 7/07
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reasonable accommodations in order to participate in this program, please contact the Center for Credit Programs to discuss your needs.
Distance Education Division of Continuing Education
250 Continuing Education Facility Iowa City, IA 52242-0907
027:053 Human Anatomy College of Liberal Arts and Sciences
Integrative Physiology
Course Contents
Course Lessons
About the Coursewriter and Instructor ................................................................... 5!Introduction: About This Course ............................................................................. 6!
Overview ........................................................................................................ 6!Course Goals .................................................................................................. 6!Required Course Materials ........................................................................... 7!How To Study ................................................................................................ 7!Web and E-mail ............................................................................................. 9!Examinations ............................................................................................... 11!Evaluation and Course Grade ...................................................................... 11!
Written Assignment #1 ............................................................................... 38!Lesson 5 Integumentary System ........................................................................... 40!Lesson 6 Bone and Skeletal Tissue ....................................................................... 45!
Written Assignment #2 ................................................................................ 51!Examination #1 ............................................................................................ 51!
UNIT 3 MOVEMENT ............................................................................................ 52!Lesson 7 The Axial Skeleton .................................................................................. 53!Lesson 8 The Appendicular Skeleton .................................................................... 59!Lesson 9 Joints ...................................................................................................... 66!
Written Assignment #3 ............................................................................... 70!Lesson 10 Muscle Tissue ........................................................................................ 71!Lesson 11 Muscle System ...................................................................................... 77!
Written Assignment #4 ............................................................................... 83!Examination #2 ........................................................................................... 83!
UNIT 4 INTEGRATION ........................................................................................ 85!Lesson 12 Nervous Tissue ..................................................................................... 86!Lesson 13 Central Nervous System ....................................................................... 94!Lesson 14 Peripheral Nervous System ................................................................ 108!
Written Assignment #5 .............................................................................. 114!Lesson 15 Autonomic Nervous System ................................................................ 116!
Written Assignment #6 .............................................................................. 121!Lesson 16 Special Senses ...................................................................................... 122!
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Lesson 17 Endocrine System ............................................................................... 129!Examination #3 .......................................................................................... 135!
UNIT 5 VISCERAL SYSTEMS............................................................................. 136!Lesson 18 Heart .................................................................................................... 137!Lesson 19 Blood Vessels and Lymphatics ........................................................... 144!
Written Assignment #7 .............................................................................. 154!Lesson 20 Respiratory System ............................................................................. 155!Lesson 21 Digestive System ................................................................................. 162!
Written Assignment #8 ............................................................................. 169!Lesson 22 Urinary System .................................................................................. 170!Lesson 23 Reproductive System .......................................................................... 175!
Be sure to read the Distance Education (DE) Policies and Procedure before beginning this course. It is available on the ICON course site under Content; students who order the optional print material will receive a print copy by mail.
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About the Coursewriter and Instructor
KENNETH E. MOBILY received his
bachelor's and master's degrees in therapeutic
recreation and was clinical supervisor of
therapeutic recreation in Cincinnati, Ohio, for
three years. He completed his Ph.D. in 1981 from
the University of Iowa in physical education. He is
a Professor at The University of Iowa where he
teaches a variety of professional courses in
therapeutic recreation. He also teaches Human Anatomy for the
Department of Integrative Physiology at Iowa. His primary research area
vertebral, and viscera). See Figures 1.4, 1.5, 1.9, and 1.10.
3. Define regional and directional terms used in association with the
body (see Figure 1.4 and Table 1.1).
4. Understand anatomical and directional terms in relation to one
another.
5. Define mucous membranes and serous membranes. Identify the
following types of serous membranes: visceral and parietal layers of
the pleura, pericardial, and peritoneum (see Figure 1.10).
Discussion
Most people think of anatomy as the study of things you can see
with unaided vision. Although this is particularly true of the present
course, as Figure 1.1 in the text indicates, anatomy can pertain to the study
of structure at a variety of levels—from chemical through organism. We
will emphasize the study of cells, tissues (groups of similar cells that work
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together), organs (made up of two or more tissues) and systems (a
collection of organs with like functions).
Probably the most critical concept to grasp initially is that of the
anatomical position. It is illustrated in Figures 1.3 and 1.4. Note that it
consists of the body in standing position, head erect and forward, feet
shoulder-width apart, arms at sides, and palms forward. The terminology
that you will also learn in this unit is worthless if you do not know the
anatomical position. All of the terms are used in reference to the
anatomical position. Also, learn the regional terminology (1.4).
Next, study the directional terms in Table 1.1. As a self-test, cover
the definitions of terms and look at yourself in a mirror. See if you can
place each regional term on your own body correctly.
Also, try using the terminology to place body parts relative to one
another. For instance, the abdomen is ventral to the vertebral column.
(Note synonyms; I could have said that the abdomen is anterior to the
vertebral column.) Another example: the shoulder is proximal to the hand.
Try some of these out yourself.
Planes are hypothetical sheets that cut the body or anatomical
structures into two parts. As you can see in Figure 1.5, there are three
planes. The frontal plane cuts the body into front and back parts. The
transverse plane cuts the body into top and bottom parts. The saggital
(median) plane cuts the body into right and left parts. Often the parts that
a plane cuts the body into are equal halves, but this is not always true.
Body cavities are spaces that contain structures. The principal body
cavities you have to know are given in Figure 1.9. Note that the ventral
body cavity is further subdivided into thoracic and abdominopelvic.
Likewise, the dorsal body cavity is subdivided into the cranial cavity and
vertebral cavity. In turn, the thoracic cavity contains special spaces that
house the heart and accessory cardiac structures (pericardial cavity in the
mediastinum) and the lungs (two pleural cavities). Any structure found
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within the ventral body cavity is referred to as viscera. Thus, viscera labels
a category of organs which includes the heart, lungs, small intestines,
stomach, and so on.
Now turn to Figure 1.2 and study the placement of systems in the
body cavities. Some vital organs are exclusively located within certain body
cavities. Place the brain, spinal cord, heart, lungs, and digestive system
into body cavities for practice.
Mucous membranes are found lining tubes entering or exiting the
body. Mucous secreted onto these membranes serves a protective function.
For instance, the mucous membranes lining the nasal cavity and upper
respiratory tract trap inspired pollutants and pollens. Mucous membranes
also line the oral cavity and rectum.
Most of the organs in the ventral body cavity are completely or
partially covered by serous membranes. Serous membranes are double
layered and have an outer parietal layer and an inner visceral layer (see
Figure 1.10). The visceral layer actually adheres closely to the organ. The
layers are identified by organ, for example, the heart is surrounded by a
parietal pericardium and an inner visceral pericardium (see Figure 1.10).
The inner visceral layer actually adheres closely to the organ. The
layers are identified by organ; for example, each lung is surrounded by a
parietal plevia and a visceral pleura. A slight space between the two serous
layers contains serous fluid, which acts as a lubricant for the movements
made by organs when they are
active.
Sample Questions
Questions 1-7 require you
to identify planes or directions
indicated on the figure.
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Foils for Questions 1-7:
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a. saggital b. transverse c. frontal d. cranial e. caudal f. lateral g. medial 1. This is the ______ direction.
2. This is the ______ direction.
3. This is the ______ plane.
4. This is the ______ plane.
5. This is the ______ direction.
6. This is the ______ direction.
7. This is the ______ plane.
8. Which of the following is incorrect about anatomical relations to the palm of the hand in the anatomical position? a. The palm is anterior to the dorsal surface of the hand. b. The hand is distal to the shoulder. c. The hand is medial to the abdominopelvic cavity. d. The hand is cranial to the thigh.
9. The lungs are located in this space.
a. dorsal body cavity b. abdominal cavity c. mediastinum d. thoracic cavity
10. What is the opposite of superficial?
a. lateral b. proximal c. internal or deep d. ipsilateral
Fertilization occurs in the distal (lateral) one third of the uterine
(Fallopian) tube of the female (see Figure 3.3). It results from the union of
an egg cell and a sperm cell, creating a new cell called a zygote. Soon after
fertilization occurs, the zygote begins to divide rapidly and form smaller
segments called blastomeres. This process of rapid cell division is referred
to as cleavage. By the time the dividing zygote nears the medial section of
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the uterine tube, it is known as a morula ("mulberry," ball of cells). The
morula is ready to begin the next phase of embryonic life, implantation.
The morula enters the uterus of the female about day four or five
following fertilization. In doing so the morula also begins to change its
internal anatomy (see Figure 3.4). Cells in the center begin to differentiate
(specialize) and form an inner cell mass (see Figure 3.3e). The remaining
space on the inside is represented by a space known as the blastocyst
cavity. The structure that was referred to as a morula when it entered the
uterus is now known as the blastocyst, with an inner cell mass and outside
cells known as the trophoblast.
The trophoblast cells on the outside of the blastocyst are
responsible for implanting the blastocyst into the uterine wall where it
may thrive in a nutrient rich environment until the fetal membranes can
fully develop and supply the growing infant with needed oxygen and
nutrients from the mother. The trophoblast accomplishes this task by
secreting powerful digestive enzymes that help the blastocyst "eat" its way
into the endometrium (inner layer of the uterine wall). As this process of
implantation occurs, note (see Figure 3.4) that the inner cell mass of the
blastocyst is beginning to change.
These changes signal the beginning of the next stage of embryonic
development, gastrulation. Gastrulation means cell movement, although
the process amounts to more than simply the movement of cells. By
around day nine (see Figure 3.4) the inner cell mass is made up of two
layers of cells, the epiblast and the hypoblast. The movement of cells of the
epiblast constitutes the process of gastrulation seen in Figure 3.5.
The beginning of the formation of the primary germ layers is
indicated by the appearance of the primitive streak, a raised groove on the
external surface of the epiblast (see Figures 3.5 and 3.6). The end result of
the process of cell movement will be the creation of a three-layered
embryonic disc in place of the earlier two-layered disc. The new three-
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layered disc will be comprised of the primary germ layers, the cells that
will form all of the structures that will become the infant.
Formation of the primary germ layers occurs when the cells of the
epiblast invaginate at the primitive streak in two successive waves. The
first cells to invaginate or "tuck under" become the endoderm and the
second group of cells invaginate to become the mesoderm. Cells that
remain in the original position of the epiblast cells become the ectoderm.
Figures 3.5 and 3.6 also demonstrate the formation of another
structure about the same time as gastrulation occurs, the notochord. The
notochord can be thought of as a precursor to the adult vertebral column.
But make certain to understand two things at this point:
1. The notochord is not part of the spinal cord, although it does
contribute to the formation of a structure found in the vertebral
column in adult life (the intervertebral disc).
2. The vertebral column is not the same thing as the spinal cord; the
latter is the nervous component housed within the vertebral
column.
However, the appearance of the notochord does correlate with the
development of the nervous system, derived from some of the cells of the
ectoderm. Figure 3.7 illustrates the process of neurulation, the formation
of the nervous system from the overlying ectoderm. Most of the process is
pretty obvious in Figure 3.7. Cells superior to the primitive node (the
swelling at one end of the notochord) differentiate and thicken, producing
a neural plate. The plate then deepens into a groove, which in turn folds
over itself, forming a neural tube. The superior extent of the neural tube
becomes the brain. The remainder develops into the spinal cord.
At the same time the neural tube is developing, cells immediately
lateral to the tube are pulled along with the deepening neural groove and
come to rest just lateral to the neural tube. These cells are referred to as
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the neural crests. They will develop into a number of structures, most
significantly, sensory nerves.
Weeks three and four in the life of the embryo are very busy, and
another important development is happening in conjunction with that of
the nervous system, differentiation of the mesoderm. The same Figure 3.7
that illustrates neurulation also shows movement and differentiation of
the mesoderm cells into three distinct groups. The first is the somites or
paraxial mesoderm. These cells reside close to the central axis of the
embryo near the notochord and the neural tube. Somites will contribute to
the formation of portions of the axial skeleton, the vertebrae and ribs, the
dermal layer of the skin, and much of the muscle system.
The intermediate section of the mesoderm forms some of the
organs in the ventral body cavity (e.g., kidneys, testicles, ovaries). The
most lateral portion of the mesoderm forms the cardiovascular system,
outer components of the digestive system, parietal membranes, and bones
and ligaments of the extremities.
In mentioning the adult structures that develop from the mesoderm
alone, the student might conclude that trying to keep straight which
structures develop from which of the three primary germ layers is a
daunting task. But there is an easier way to master the task than pure rote
memory. The trick when trying to remember any classification scheme
with two or more categories is to try to remember the easier categories
first. This means the number of categories to remember will be one less
than the total number. In the present case, there are three categories to
remember: ectoderm, mesoderm, and endoderm. I am suggesting that you
need only remember two of the three, as follows.
The ectoderm forms the outer layer of the skin (epidermis), the
nervous system, some bones of the skull and some glands. The endoderm
forms the inner walls of the digestive and respiratory systems, the lower
portion of the urinary system, and some glands. Everything else is formed
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027:053 Human Anatomy
from the mesoderm. So by process of elimination, you know what is
formed from the mesoderm without having to remember its derivatives in
a rote manner. Refer to Figure 3.10 for details of the structures formed
from each germ layer.
Hence, by the end of the embryonic period (0-2 months) almost all
of the necessary structures for survival are in place. The remainder of the
gestation is referred to as the fetal period. It consists primarily of growth
and maturation of structures put in place during the embryonic period.
Moreover, most serious birth defects (congenital defects) appear in the
embryonic period. It stands to reason that the problem will be more
serious if it develops earlier, since all subsequent structures are formed
from the three layers of the embryonic disc and its subsequent folding and
cell movement. In other words, the earlier a problem develops, the more
tissues that are affected, because the problem is perpetuated or passed
along into all structures formed from the affected structure.
Several examples of the more frequent birth defects are discussed in
the "A Closer Look" box at the end of the chapter. Although I will only
discuss one of those defects below, you should have a sense of which
embryonic structures are affected relative to each of the defects listed on
your objectives. Notice how many of the birth defects listed could be
avoided by living a healthy lifestyle and not abusing substances. Maternal
health is therefore crucial to the normal development of the infant.
Spina bifida in its most severe form is a neural tube defect. It results
from a failure of the distal/caudal end of the neural tube to close. The child
is born with a lesion called a "cele," most often found in the lower lumbar
or sacral areas. The resulting deficit is typically paralysis of both lower
extremities and incontinence. The child born with spina bifida may have a
problem with the cranial end of the neural tube as well and often presents
with a condition called hydrocephalus, "water on the brain." This problem
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as well as the paralysis resulting from spina bifida can be managed with
early detection and intervention.
Sample Questions
1. The morula forms as a result of this process. a. gastrulation b. neurulation c. implantation d. cleavage
2. Cells that eventually form the three primary germ layers are derived from this structure. a. trophoblast b. blastocoel c. embryonic disc d. notochord
3. Blood vessels form from this embryonic germ layer. a. ectoderm b. mesoderm c. endoderm
4. This term refers to cell movement. a. cleavage b. gastrulation c. neurulation d. implantation
5. Stem cells are derived from this structure in the embryo (you will have to research this one by reviewing the chapter closely). a. Inner cell mass b. trophoblast c. morula d. yolk sac
Answers to Sample Questions
1. d; 2. c; 3. b; 4. b; 5. a
Go on to Lesson 3.
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UNIT 2 BASIC ORGANIZATION
Lesson 3 Cells
Lesson 4 Tissues
Written Assignment #1
Lesson 5 Integumentary System
Lesson 6 Bone and Skeletal Tissue Written Assignment #2
Examination #1
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Lesson 3 Cells
Reading Assignment
Read Chapter 2 in the text, focusing on material that pertains to
objectives listed below.
Objectives
By the end of this lesson, you should be able to:
1. Identify the structural components of a prototypical cell in an
3. Identify the role of organelles involved in a secretion pathway
illustrated in Figure 2.8.
4. Generally, define the structure and function of a chromosome
(DNA).
5. Define mitosis, dysplasia, hyperplasia, hypertrophy, and necrosis.
Discussion
In the seventeenth century, Robert Hooke, an English physician,
was the first scientist to use the term "cells." Only later did scientists come
to fully appreciate the importance of Hooke's discovery. The cell is the
basic functional unit of the body. Like any of the larger functional units we
will study, it has a structure—it is an assembly of various parts.
The most basic of these parts is the cell or plasma membrane. The
cell membrane "marks off" the cell as an entity unto itself. It is essentially
a two-layered arrangement of phospholipids and proteins (see Figure 2.2).
This two-layered enclosure controls the entrance and exit of materials into
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and out of the cell proper. You should try to get a sense of the factors that
affect the permeability of the cell membrane (e.g., size of molecule). The
cell membrane can have special places on its outer surface, called receptor
sites, to interact with certain chemicals, such as neurotransmitters and
hormones.
Within the confines of the cell membrane, we find the remaining
parts of the cell: the structures called organelles and the fluid between the
structures, called cytoplasm. Cytoplasm is largely water, making it an
excellent medium for chemical reactions.
Starting with the nucleus, then, we will continue to study the
structure and function of the other parts of the prototypical cell. You
should continuously refer back to Figure 2.1 for study of the shapes of
organelles so that you can identify them later. Notice that small
illustrations for most organelles are found throughout the chapter.
The nucleus (Figure 2.13) is the "brain" of the cell. It almost
completely determines what the cell will do. It has its own membrane,
similar in structure to the general cell membrane. Within the nucleus we
find the genetic material of life, DNA (see Figure 2.14). It appears as
chromatin or chromosomes depending on whether the cell is actively
mitotic or not. DNA, RNA, and proteins are found in the nucleolus, a small
rounded body within the nucleus proper. (We will have more to learn
about DNA later.)
Ribosomes are sometimes called the "anvils" of the cell because
they are the sites where proteins are "forged" (assembled). Amino acids,
the building blocks of proteins, are brought to the ribosome for assembly
into a protein. Ribosomes can be attached or free. Attached ribosomes
appear as small dots (see Figure 2.6 for ribosomes attached to
endoplasmic reticulum) adhering to another structure, the endoplasmic
reticulum. Free ribosomes are just that—free-appearing in the cytoplasm
as unattached dots.
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Endoplasmic reticulum (Figure 2.5) appears as adjacent walls that
form channels, usually found close to the nucleus. If the endoplasmic
reticulum has ribosomes attached, it is called rough or granular
endoplasmic reticulum. If it does not have ribosomes attached, it is
referred to as a smooth or agranular endoplasmic reticulum. Endoplasmic
reticulum is sometimes specialized according to tissue type. For instance,
endoplasmic reticulum in muscle cells is specialized to facilitate
contraction and therefore given a special name—sarcoplasmic reticulum.
(The sarcomere is the functional unit in a muscle cell). The most
important functions of endoplasmic reticulum are storage and
transportation of various materials, but it also helps mechanically support
the cell because of its relatively substantial presence within the cytoplasm.
The golgi apparatus (Figures 2.7 and 2.8) is thought to work with
the endoplasmic reticulum and ribosomes to complete a network
responsible for a product, generally a protein, destined for secretion from
the cell. For instance, after the ribosome produces a product, the
endoplasmic reticulum transports it to the golgi apparatus. The golgi
apparatus then "packages" the product in a way that allows it to pass
through the cell membrane more easily. The golgi apparatus appears as a
stack of "pancakes" with globules floating away from it. The latter are
called secretory vesicles. Secretory vesicles might contain an enzyme to
help digest food, if the cell is in the stomach, or a different product if the
cell is located elsewhere in the body.
The nucleus, endoplasmic reticulum with ribosomes, and the golgi
apparatus, are linked together in cells that actively produce and secrete
useful products (e.g., digestive enzymes). Study Figure 2.8 to see how
these organelles work together in a secretion pathway.
The mitochondrion is often referred to as the "powerhouse" of the
cell because it is responsible for synthesizing energy for the cell's use in the
form of ATP. (ATP molecules can be thought of as batteries.) As can be
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observed in Figure 2.10, the mitochondrion looks like an oblong capsule or
coated tablet on the outside. But on the inside, viewed in the cut-away
portion of Figure 2.9, the mitochondrion has many convolutions or
"shelves" known as cristae. These shelves are produced when the inner
membrane of the mitochondrion folds onto itself. This folding
exponentially increases the surface area for reactions, and hence, energy
formation. (By the way, such folding is a good example of how function is
facilitated by structure.) Because of their involvement in energy formation,
you might logically suppose that very active cells would contain many
mitochondria. This is precisely the case. For instance, muscle cells contain
many mitochondria.
Lysosomes are round structures with fairly thick membranes to
hold their contents—powerful enzymes with the potential to destroy the
cell itself. They are also produced by the golgi apparatus. Lysosomes are
not smooth spheres; rather, their surface is irregular and uneven. Because
of their contents, lysosomes are sometimes called the "suicide packets" of
the cell. More often, however, in the healthy cell, the lysosome can destroy
unwanted invaders that pose a danger to the integrity of the cell or ingest
other "worn out" cellular organelles. For instance, white blood cells
(leukocytes) contain many lysosomes.
Centrioles are long, narrow cylinders located within a greater
structure called a centrosome (see Figure 2.12). Centrioles arrange
themselves in a very organized fashion, appearing as nine evenly spaced
bundles of microtubules. Viewed from the side (Figure 2.12c), the
microtubules of the centriole look like spokes in a wheel. Centrioles are
active in the process of mitosis (cell duplication). They seem to assist in
the movements of chromosomes during mitosis.
DNA is frequently studied in its highly organized state, in the form
of a chromosome, a state it assumes just prior to and during cell division.
DNA looks like a ladder that has been twisted. This is often called a double
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helix arrangement of DNA. The vertical portions of the ladder are
composed of repeating sequences of sugars and phosphates (Figure 2.14).
The horizontal parts of the ladder, where one might place a foot, are made
up of two nitrogen bases. There are four different bases (see "C," "G," "A,"
and "T" in Figure 2.14) in all and the ways in which these bases are
matched up form a sort of code or blueprint for the formation of proteins
and RNA. This is accomplished by portions of the DNA molecule
unraveling and fresh bases being matched up or paired with those
exposed. Accordingly, specific lengths of the DNA molecule correspond to
specific proteins or types of RNA. Lastly, when the entire DNA molecule
unravels, it can completely replicate itself. This happens just before
duplication of the entire cell during the process of mitosis.
Mitosis (Figure 2.18) is the type of cell division that results in two
new/daughter cells that are identical to the parent cell—each has the exact
same 23 pairs of chromosomes. Mitosis is necessary for growth and
development early in life, and for maintenance of tissues the remainder of
life.
Interphase is basically the time in a cell's life between mitotic
divisions (see Figure 2.17). Mitosis consists of four phases that result in the
formation of two daughter cells genetically identical to the parent cell.
Interphase and mitosis are summarized in Figure 2.17.
During interphase the cell is preparing for cell division as well as
carrying on its normal functions. The cell grows and synthesizes an
identical set of DNA for use in the subsequent division. As you can see in
Figure 2.17, interphase takes quite a long time compared to all four of the
phases that make up mitosis.
You do not need to know the details of mitotic division. You should
be able to define mitosis and explain its importance for growth and
maintenance.
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Look up definitions of terms listed in the final objective at the end
of the chapter. Also, look over the "A Closer Look" window at the end of
the chapter, which discusses cancer, and read the short section on aging.
Sample Questions
Try to answer the questions below after you have read Chapter 2,
satisfied the objectives, and studied the figures indicated. Use the
questions as a self-test. If you miss some of the questions, go back to the
chapter to study the material again and find out why you missed the
question.
1. Name the organelle associated with packaging and secreting materials from the cell. a. golgi apparatus b. mitochondrion c. lysosome d. nucleus
2. Where would you expect to find the most ATP? a. in the cell membrane b. in the DNA molecule c. in the mitochondrion d. in the chromosomes
3. Name the structure whose spherical, external surface is irregular; it contains enzymes strong enough to destroy the entire cell. a. centriole b. nucleus c. golgi complex d. lysosome
Answers to Sample Questions
1. a; 2. c; 3. d
Go on to lesson 4.
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Lesson 4 Tissues
Reading Assignment
Read Chapter 4 and pages 125-126 in your textbook with emphasis
on the topics covered by the objectives below.
Objectives
By the end of this lesson, you should be able to:
1. Define a tissue and describe four basic tissue types.
2. Identify the functions of epithelium. Contrast the general
characteristic of epithelium with the general characteristics of
connective tissue: proportion of matrix, proportion of cells, vascular
3. Briefly list the structure and function of simple, stratified, pseudo-
stratified, transitional and glandular epithelium (Figure 4.3).
4. Identify the four types of adult connective tissue (CT proper,
cartilage, bone, blood) and describe the following structures found
in loose (aveolar) connective tissue (Figure 4.11): fibrocytes,
collagen fibers, elastic fibers, reticular fibers, and ground substance
or matrix.
5. Compare and contrast the different types of connective tissue:
connective tissue proper, cartilage, bone, and blood (see Figures
4.9, 4.12).
6. Describe the inflammatory response and repair process; identify the
four classic symptoms of the inflammatory response.
Discussion
A tissue is a group of similar cells that work together to accomplish
a common purpose. We will spend considerable time later in this course
studying two of the four basic tissue types—muscle and nervous tissue.
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The remaining types of tissue are epithelial and connective. Histology is
the study of structure and function of tissues. For now, you should get a
general sense of how to discriminate between the four tissue types. Most
people have difficulty discriminating epithelial and connective tissues, so
we will spend most of the time in this lesson focusing on those two tissue
types.
Basically, epithelial tissue does two things. It covers things
(covering/lining epithelium) or it forms glands. Regardless of the type,
epithelium has some definite characteristics you can use to distinguish it
from connective tissue. These include: tightly packed cells, little
intercellular substance (called matrix), a basement membrane (that
supports epithelium), derived from all three layers of the embryo
(ectoderm, mesoderm, endoderm) and no direct blood supply (avascular)
(see Figures 4.1–4.2).
Covering or lining epithelial tissue can be further sub-divided on
the basis of the number of layers of cells and whether or not all of the cells
reach the surface or not (see Figure 4.3). Simple epithelium means there is
a single layer of cells (classified by shapes: squamous, cuboidal,
columnar), whereas stratified epithelium has several layers of variously
shaped cells. The former are found in areas where there is little wear and
where materials have to move into and out of channels easily (like the
lining of capillaries of the vascular system). The latter, stratified-type of
epithelium is found in areas that experience considerable wear and tear
(skin, bladder, and some parts of the digestive tract). A specialized type of
stratified epithelium is known as transitional. It is specialized to distend
(stretch). The third general type of epithelium is called pseudostratified
(pseudo means "false") epithelium (see Figure 4.3d). This is because the
cell arrangement looks like it has several layers, but in reality there is only
one layer of cells. The pseudostratified appearance is attributable to the
fact that not all of the cells reach the lumen of the channel they line.
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The second term that is used to label an epithelial tissue (e.g.,
squamous) refers to the cell shape. The various types of epithelium are
illustrated in Figure 4.3. But you are only expected to know the
significance of simple, stratified, or glandular epithelium; you do not have
to know cell shape.
Glandular epithelium comprises both types of glands, exocrine and
endocrine. For now, you simply need to know that endocrine glands
always secrete hormones; exocrine glands never secrete hormones
(although their products are useful). We will discuss glands in more detail
in the lesson on the endocrine system.
Connective tissue can be discriminated from epithelium on the
basis of its rich vascular supply (with the exception of adult cartilage and
ligament), widely separated cells, and substantial intercellular substance
(matrix). Connective tissue is derived exclusively from the mesoderm of
the embryo. Connective tissue does not cover or line, rather it occurs
beneath the surface, deep to covering or lining epithelium. However, the
connective tissue category probably represents a rather surprising
collection of structures that are seemingly unrelated. Bone, cartilage,
tendons, ligaments, and blood are all categorized as connective tissue.
However, they all share in common the characteristics of connective tissue
with respect to vascular supply, cell to intercellular matrix relationship,
embryonic derivative, and location (see Figure 4.9).
For now, we will look at loose (areolar) connective tissue as the
prototypical connective tissue and see what it is made of. Fundamentally,
the remaining sub-types of connective tissue are differentiated on the basis
of fiber types and amounts, cell types, and consistency of matrix. The
matrix of loose connective tissue is composed of a viscous ground
substance. In its normal state, ground substance facilitates the movement
of materials through connective tissue.
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The matrix also includes fibers, mostly collagenous, with some
elastic. As suggested earlier, the amount and type of fiber helps determine
the type of connective tissue. For example, if there is a large amount of the
collagenous fiber type, with very little fluid between, the connective tissue
is likely a tendon or ligament. Collagen fibers are very tough and resist
stretching. Elastic fibers are tough and can be stretched (hence the title
"elastic"). Finally, reticular fibers are often associated with soft organs
(like the liver) where they provide a framework or structure for the organ.
The typical cell of loose connective tissue is the fibroblast/fibrocyte
(see Figures 4.9 and 4.11 and Table 4.2). Authorities believe that fibrocytes
are responsible for production of many of the fibers of loose connective
tissue and the ground substance of the matrix.
Several other cells (macrophages, plasma cells, mast cells, various
white blood cells) can be found in loose connective tissue. Their primary
responsibility is defense of the body against disease and infection. The
placement of these cells that comprise part of the body's immune response
makes sense since they serve to form a second line of defense if a "germ"
finds access to the body through a cut that penetrates the epidermis.
Loose connective tissue is only one of several types of connective
tissue proper. The others are dense regular, dense irregular, elastic,
reticular, and adipose. Each is specialized according to the amount and
types of fibers found in the matrix.
Dense connective tissue is dominated by collagen fibers (Figure
4.12). If the collagen fibers line up in parallel rows, then it is dense regular
connective tissue. This type of connective tissue is characteristic of
ligaments and tendons, where a lot of strength is needed in one direction.
If the fibers run in various directions, then it is dense irregular connective
tissue. This is characteristic of the dermis layer of the skin (covered in the
next lesson) the periosteum of bone, and the capsules surrounding
synovial joints.
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Reticular connective tissue (Figure 4.12) is understandably
dominated by reticular fibers. Reticular fibers are capable of forming a
framework or "scaffold" for other tissues to attach to. This is why reticular
connective tissue characteristically forms the structural part (stroma) of
many soft organs, such as the liver, spleen, and lymph nodes.
Elastic connective tissue (Figure 4.12) can be found in large arteries
near the heart that experience a lot of stretching when blood is forcefully
ejected into them from the right or left ventricle. Elastic connective tissue
can also be found in ligmentum flavum between the lamina of two
vertebrae where considerable stretching occurs. As you might have
deduced, elastic connective tissue is distinguished from others by virtue of
its generous compliment of elastic fibers.
Adipose tissue (see Figure 4.12) is made up of fat cells (adipocytes)
and is designed for storage of fat droplets within the cytoplasm of the fat
cells.
Mature cartilage distinguishes itself from connective tissue proper
in several ways. First, unlike most connective tissue, cartilage does not
receive a good vascular supply. Second, the typical cell found in cartilage is
a chondrocyte and not a fibrocyte as in connective tissue proper. Finally,
the matrix of cartilage is semi-solid and less fluid than that of loose
connective tissue.
Cartilage comes in three varieties (see Figures 4.12 and 6.1). First
and most plentiful is hyaline cartilage. Hyaline cartilage makes up the
embryonic skeleton, the costal cartilages running from the ribs to the
sternum, and it covers the articular surfaces of bones as they enter into
joints.
Fibrocartilage is considerably less plentiful. It is found between
vertebrae as the outer ring of intervertebral disks, between the two pubic
bones of the bony pelvis as the symphysis pubis, and within some joints as
articular discs (e.g., menisci of the knee).
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The last type of cartilage is elastic cartilage. It is found in only a few
places as well. Elastic cartilage comprises the epiglottis that covers the
trachea as you swallow so that food does not find its way into your trachea
("windpipe"). It also makes up the auditory (eustachian) tube and the
external ear. Hence, you can distort and bend the external ear and it will
return to its original shape.
Bone (see Figure 4.12) is also a type of connective tissue that we will
discuss in another lesson. Like all other connective tissue, it has only a few
cells (osteocytes) scattered in a matrix with collagen fibers. Everyday
observation confirms that a major difference between bone and other
types of connective tissue is that the matrix of bone is solid. This is
because of the deposition of minerals between the osteocytes.
Likewise, blood is also considered connective tissue because it
shares the same features. It has a few cells, erythrocytes and leukocytes,
scattered among a large amount of intercellular matrix called plasma.
Figure 4.9 summarizes the development of all of the types of
connective tissue from the embryonic mesenchyme (mesoderm).
The remaining two tissue types are muscle (Figure 4.14) and nerve
(Figure 4.15). Muscle is specialized to shorten (contract), whereas nervous
tissue is specialized to conduct nerve impulses from place to place. Muscle
and nervous tissue are important enough to warrant in-depth coverage
later in this course.
For now, muscle tissue is found in three types. Skeletal muscle
moves the skeleton. Cardiac muscle is found in the middle wall of the
heart. Smooth muscle comprises the muscular layer of the walls of various
tube-systems (viscera), such as the vascular system.
Nerve tissue is divided into the central nervous system (brain,
spinal cord) and peripheral nervous system (peripheral nerves). It is
specialized to transport "information" we know as a nerve impulse.
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Sample Questions
Make sure you have read the material thoroughly and satisfied the
objectives at the beginning of this lesson before attempting the sample
questions. Try the questions without the aid of book or notes. If you miss a
question, go back and try to determine why you missed it.
1. Which of the following is not a type of epithelial tissue? a. simple epithelium b. cartilage c. stratified epithelium d. exocrine gland
2. Which cell is typically found in loose connective tissue? a. chondroblast b. fibroblast c. osteoblast d. mesenchymal
3. Which statement best describes epithelium? a. It is always arranged as a single layer of cells. b. It contains a large amount of matrix. c. It has an abundant blood supply. d. It has a free border.
4. Tearing a ligament would mean you have sustained damage to this type of tissue. a. epithelial tissue b. connective tissue c. muscle tissue d. nervous tissue
5. A group of cells operating together to perform a specialized activity is called by this name. a. organ b. system c. organism d. tissue
Answers to Sample Questions
1. b; 2. b; 3. d; 4. b; 5. d
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Written Assignment #1
Instructions
Instructions for submitting assignments electronically in the ICON
Drop Box are posted on the ICON course site under "Submit
Assignments."
Description
This assignment is worth 10 points.
Organs are defined as structures that are made up of more than one
tissue. This means that tissues in organs work cooperatively with one
another to accomplish necessary tasks. This assignment is intended to
help you appreciate the cooperative relationships among tissues within
organs, specifically the skin and muscles (both are organs and systems).
Answer all three of the questions below for this assignment.
1. Any given skeletal (voluntary) muscle qualifies as an organ.
Therefore, a cross section through a muscle such as the biceps
brachii would reveal two or more tissue types. In fact, all four of the
basic tissue types are represented in the biceps brachii. Explain,
specifically, where each of the four tissue types is found within the
biceps brachii. (Hint—remember the muscle will have blood supply,
nerve supply, and a means to attach to a bone to produce
movement).
2. Skin (the integument) affords the student an excellent opportunity
to study how epithelial tissue and connective tissue work in
cooperation. One of the major functions of the skin is protection.
Explain how the epithelial portion of the skin (epidermis) and the
connective tissue part of the skin (dermis) serve to protect the
individual.
3. Epithelial cells are the frequent origins of several types of cancer
(e.g., skin cancer, lung cancer, …). Explain why this is the case.
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Identify and explain the attribute of epithelial tissue that is
associated with cancer and how this very same attribute is
beneficial to humans as they age.
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Lesson 5 Integumentary System
Reading Assignment
Read Chapter 5 in the text, paying special attention to answering
the objectives specified below.
Objectives
By the end of this lesson, you should be able to:
1. Define and describe the skin as an organ, and the integumentary
system.
2. Know the functions of the integument.
3. Identify cells typically found in the epidermis, including:
The structural classification of joints basically looks at how the joint
is held together. If the joint is bound by fibrous connective tissue
(remember the strength of collagen fibers), then it is a fibrous joint
(suture, syndesnosis).
Cartilaginous joints are bound together by (you guessed it!)
cartilage. There are two types of cartilagenous joints. We have actually
considered a synchondrosis already—technically, the epiphyseal plate is
considered a synchondrosis type joint. Costal cartilages also qualify the
articulations between ribs and sternum as a syndhondrosis. Intervertebral
discs qualify as a symphyseal type of cartilaginous joint, the connective
tissue is fibrocartilage.
The more interesting joints for the purposes of sport, exercise, and
human movement are the freely movable joints. This category exclusively
includes synovial joints.
You should study and know the prototypical synovial joint (Figure
9.3) very well. Pay particular attention to the minimal features necessary
for a joint to be classified as a synovial type: joint cavity, articular capsule,
and articular cartilage. As you will find out later, there are additional
structures that you might find in a synovial joint (articular discs,
ligaments, etc.), but those listed above are the minimum number of
structures for a joint to qualify for the synovial category. Synovial joints
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get their name from the synovial membrane that lines the inside of the
joint capsule and secretes the lubricating synovial fluid.
You should next study the types of movements possible at a
synovial joint. I would recommend you use Figures 9.5 and 9.6 and
practice each of the movements. Next, have a friend, spouse, or child test
you by doing each of the movements. Your task would be then to recognize
each of the movements demonstrated.
While you are practicing each of the movements, you might want to
think about those anatomical features that limit movement. There are four
factors that limit movement: muscle strength, tension of ligaments, bone
morphology (shape), and soft tissues. For instance, the shape (structure)
of the trochlear notch of the ulna and the trochlea of the humerus allow for
only one type of angular movement—flexion/extension.
Note some clarifications for movements. In the hand, taking the
fingers away from the mid-line of the hand is abduction; the opposite is
adduction. Technically, circumduction is only possible at ball and socket
joints.
Next, study the different subtypes of synovial joints based on the
shapes of articulating bones. As you can see in Figure 9.7, the shapes
(structure) of articulating bones largely determine the kind of
movement(s) allowed at a synovial joint. Also, once you believe you have
learned synovial joint types fairly well, try to determine the kinds of
movements allowed at each. We will reinforce the relationship between the
structure (shape) of synovial joints and movements possible through the
written assignment at the end of this lesson.
Now for the tough part. Work your way through each of the joints
listed in your objectives and study the figures (9.8 through 9.15) that
pertain to each. Try to get a general sense of how the ligaments are placed.
Identify other accessory structures (articular discs, etc.). For example, you
should know that collateral ligaments prevent abduction and adduction in
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the coronal/frontal plane at hinge joints. Hence, collateral ligaments
stabilize joints such as the elbow and the knee.
Don't overlook the articulating bones, the type of joint you are
studying, and the movements possible at each joint listed in the objectives.
Make sure to study the material in Table 9.2 that pertains to each joint.
Take breaks by reading the clinical applications identified in Objective 8.
Remember, do not try to learn everything in one or two nights. Also
remember to test yourself using the copy machine and label method
employed in earlier lessons.
Sample Questions
1. What is the name given to a joint that is united by a dense ligament of fibrous connective tissue? a. gliding joint b. synovial joint c. cartlaginous joint d. fibrous joint
2. What is the clinical term applied to excessive stretching or tearing of
ligaments? a. dislocation b. strain c. sprain d. bursitis
3. This is the special name given to extension of the foot at the ankle joint.
a. hyperextension b. plantar flexion c. dorsiflexion d. abduction
4. Which of the following is not a synovial joint?
a. plane b. hinge c. symphysis d. ball and socket
5. Which ligament below is found at the elbow joint?
a. radial collateral
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b. zona orbicularis c. transverse acetabular d. posterior cruciate
Answers to Sample Questions
1. d; 2. c; 3. b; 4. c; 5. a
Written Assignment #3
Instructions
Instructions for submitting assignments electronically in the ICON
Drop Box are posted on the ICON course site under "Submit
Assignments."
Description
This assignment is worth 10 points.
1. Compare and contrast knee and elbow joints, noting similarities
and differences between the two. Think about structural and
functional joint type, placement and number of ligaments, number
of bones and articulations in each joint, and movements possible at
each joint.
2. The gleno-humeral joint and the hip joint both qualify as ball and
socket joints. Explain why the gleno-humeral joint seems to be
more mobile then the hip even though both joints are ball and
socket. Explain why the gleno-humeral joint is injured more
frequently.
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Lesson 10 Muscle Tissue
Reading Assignment
Read Chapter 10 and pages 540-542; 649-651 in your textbook. It is
important to really follow your objectives closely because some aspects of
muscle function are not your responsibility. Of course, I still recommend
that you read everything, but spend more time studying the objectives.
Objectives
By the end of this lesson, you should be able to:
1. Describe the major characteristics and functions of muscle tissue.
Identify the parts of a muscle (origin, belly, insertion).
2. Define and contrast the three different types of muscle (skeletal,
cardiac, smooth). See Table 10.2.
3. Identify and describe the different connective tissue components in
muscle (Figure 10.1).
4. Define the basic components of a skeletal muscle cell (fiber). (See
Figures 10.4 and 10.6.) Draw a sarcomere. Briefly explain muscle
contraction at the level of the sarcomere (see Figures 10.4 and
10.8).
5. Identify the components of a neuromuscular junction (see Figure
10.9). Define a motor unit and its implications for precise
movements versus gross body movements.
6. Discuss the concept of muscle tone and its implications for posture.
7. Define these clinical applications: muscular dystrophy, muscle
strains, atrophy, hypertrophy, fibromyalgia, and a muscle cramp.
Summarize the detrimental effects of steroid use.
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Discussion
To no one's surprise, muscle tissue is specialized to contract, to
become shorter. In this way, muscles move the bones they are attached to.
However, excitability, extensibility and elasticity, also number among the
characteristics of muscle tissue.
There are three different types of muscles (see Table 10.2) that can
be distinguished on the bases of voluntary versus involuntary control,
striated versus non-striated, location, fiber shape and number of nuclei.
Skeletal muscle is sometimes called voluntary muscle because we have
conscious control over it. But there are many important motor activities
that we do not consciously control. Most of us know that we do not have to
consciously think to make our hearts (cardiac muscle) beat (a good thing,
too, since I'm very forgetful). But involuntary muscle (smooth muscle) also
lines the small intestine and its contractions help us digest food.
Involuntary muscle (smooth muscle) lines the walls of many medium-
sized and small arteries and its contraction (and relaxation) helps regulate
blood flow to certain areas of the body. We will spend most of this lesson
focused on skeletal muscle.
Skeletal muscles move the skeleton and are what most people think
of as muscles. Most skeletal muscles have two attachments (or more)
between bones and the contracting muscle. The muscle is referred to as
the belly or gaster. The attachment that moves is called the insertion; the
stable attachment is the origin.
People are also sometimes surprised to learn that muscle tissue
proper contains connective tissue. The primary connective tissue
components are illustrated in Figure 10.1. Endomysium surrounds each
muscle cell (also called a muscle fiber). Perimysium surrounds a group of
muscle cells, called a fascicle. Finally, epimysium surrounds the entire
muscle. These three layers of connective tissue converge on the
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attachments of muscle to bone and actually become a cord of connective
tissue called a tendon.
The important thing to remember when looking at the structure of a
muscle cell is to understand when you are looking at a cell and when you
are looking at something inside a cell. A muscle fiber and a muscle cell are
one and the same thing, though this can be somewhat confusing. Look for
the endomysium because you know that it surrounds one cell at a time.
Like any other cell, a muscle fiber (see Figure 10.4 and 10.6) is
covered by a cell membrane, known as a sarcolemma. However, muscle
cells are usually studied in smaller functional units. These functional units,
called sarcomeres, can be thought of in the same way as any other
intracellular organelle. (Precisely speaking, sarcomeres are not organelles.
But it makes sense to think about them as organelles because then you
know you are looking at something inside a cell and not looking at the
outside of a cell.) A sarcomere is pictured in Figure 10.4d. Sarcomeres are
defined as running from Z line to Z line and contain the contractile
proteins (myofilaments) that result in the shortening of the muscle proper
and the production of movement. There are thick myofilaments (myosin)
and thin myofilaments (actin), which you can see in Figure 10.4. Together,
the Z lines, thick myofilaments and thin myofilaments, overlap
intermittently to form three areas or bands. There is an I band, and an A
band and an H zone. In a relaxed state the following are true (see Figure
10.7):
a. I bands contain thin myofilaments only,
b. the A band contains thick and thin myofilaments,
c. and the H zone contains only thick myofilaments.
The sliding filament theory of contraction (see Figures 10.7 and
10.8) hypothesizes that proteins within the thick and thin myofilaments
articulate to form "cross-bridges" with one another and pull the Z lines of
the sarcomere closer together. Said another way, the thin myofilaments of
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a sarcomere move inward, toward one another during contraction.
Multiplied many times in many sarcomeres through a muscle, the result is
observable contraction (shortening) of the muscle and movement. Now
study Figures 10.7 and 10.8 and deduce what happens to the A and I bands
and H zone after contraction.
A neuromuscular junction is crucial to muscle contraction. It
represents the meeting place of nerve and muscle tissues, the place where
the nervous impulse (command to contract) is actually given to the muscle
as a chemical message. Figure 10.9 shows the structure of a
neuromuscular junction. Note the components of the neuromuscular
junction. The chemical message or command is contained within synaptic
vesicles in the nerve fiber. When a nervous impulse reaches the end of the
nerve fiber, it causes the vesicles to release their chemical message in the
form of a neurotransmitter. The neurotransmitter then crosses the
synaptic cleft to bind with the sarcolemma (muscle cell membrane) to
stimulate the muscle fiber. Neurotransmitters differ depending upon the
tissue type, but the neurotransmitter for skeletal muscle is acetylcholine.
A motor unit consists of a motor neuron (motor nerve cell) and all
of the muscle cells it stimulates. There are gross and fine motor units.
Gross motor units have one neuron innervating many muscle cells (up to
several hundred), whereas fine motor units have far less muscle cells
innervated by a motor neuron (ten and sometimes less). Fine motor units
are found in areas where precise movement is required, such as the hands,
the face, and muscles of speech. Muscles responsible for large or gross
movements, like running or jumping, tend to have gross motor units
(muscles of the back, trunk, thighs, and legs).
Muscle tone (not to be confused with an isometric contraction) is
the state of partial contraction assumed by skeletal muscle. Tone confers
resilience on a skeletal muscle. But the number of muscle fibers in the
muscle that are contracting is not enough to produce observable
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movement. Muscle tone is essential to maintaining good posture because
it usually amounts to holding the position of the body steady while other
parts work (e.g., hands and upper extremities).
Muscle tissue is not often affected by pathology, though it is often
the site of relatively minor injury (strains, cramps). Some disorders of
muscles cause a decrease in muscle size, called atrophy, because of a loss
of contractile units within a muscle fiber. Muscular dystrophy, for
example, is an inherited disorder of muscle tissue which causes a
progressive loss of contractile units in muscle, with replacement by fat and
connective tissue. However, pathology is not the only cause of atrophy in
the muscle system; simple disuse, lack of exercise, will also result in
atrophy.
Unlike muscular dystrophy, myasthenia gravis affects the neuro
muscular junction. Anti-bodies produced by the individual block
transmission of a nerve impulse at the neuromuscular junction causing
weakness and early fatigue.
Fibromyalgia is sometimes called arthritis of the muscle system. Its
symptoms include pain over numerous "tender points" across the body.
The patient is also plagued by sleep disturbance, often accompanied by
depression.
Unfortunately, social pressure on youth often leads to drug abuse in
an effort to increase the strength of a muscle. Although a muscle will get
larger (hypertrophy) and stronger in response to exercise, use of steroids
(synthesized testosterone-like substances) will cause hypertrophy as well.
Serious physical complications associated with steroid abuse present
significant danger (see page 254).
Sample Questions
1. Name the property that gives muscle tissue the ability to receive and respond to stimuli.
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a. contractility b. excitability c. elasticity d. extensibility
2. Name the stationary attachment of a muscle.
a. tendon b. aponeurosis c. origin d. insertion
3. What is the connective tissue component of skeletal muscle that
surrounds a muscle fascicle? a. perimysium b. epimysium c. endomysium d. tendomysium
4. The term motor unit is applied to this.
a. connective tissue coverings around a muscle b. the union of a muscle's tendon with the periostium of bone c. a motor neuron and the muscle fibers it stimulates d. the triad of a skeletal muscle fiber
5. This portion of a sarcomere contains thick myofilaments only.
a. A band b. I band c. H zone d. Z line
Answers to Sample Questions
1. b; 2. c; 3. a; 4. c; 5. c
Go on to Lesson 11.
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Lesson 11 Muscle System
Reading Assignment
Read Chapter 11 in your textbook. As with the past few chapters
now, you will find Chapter 11 involves more studying of figures than actual
reading. Also, as before, I strongly urge you to take the time to learn the
peroneus longus, peroneus brevis. See Figures 11.22, 11.23
and 11.24.
4. Describe most body movements as activities of groups of muscles
by explaining the roles of agonists, and antagonists.
Discussion
You have probably already deduced that the muscular system
should be entitled more specifically "the skeletal muscular system"
because the lesson involves exclusively those muscles that produce
observable and voluntary movement. So any use of the word "muscle" in
this lesson means skeletal muscle.
Analysis of muscle actions involves a set of terms used to describe
what a muscle is doing at a particular time, during a particular movement.
An agonist refers to the muscle(s) doing the work and shortening. The
antagonist is the muscle that must relax in order for the movement to
occur. The antagonist will usually produce the movement that is the exact
opposite of the movement produced by the agonist. As you work your way
through the objectives on specific muscles, try to think in terms of group
actions and the muscles that are agonists and antagonists. Concentrate on
flexion/extension, abduction/adduction and rotation. Muscles that
produce the same action are also said to be synergists.
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Figure 11.2 illustrates the three different types of levers: first,
second and third class. Analogies to a see-saw, wheelbarrow, and lifting an
object with tweezers are provided. Note that the most common type of
lever is the third class. Further note that third class levers are at a
mechanical disadvantage, but are well designed for rapid movement over
an extensive range of motion (as in running or throwing).
I would advise that you tackle the list of muscles you see in
Objective 3 in a logical manner. First, try to identify the major muscles in
Figure 11.7. Most people think it is helpful to study: 1. muscles acting on
the trunk and axial skeleton, 2. muscles of the shoulder girdle and upper
extremity, 3. muscles on the pelvic girdle and lower extremity. After you
can identify the muscles listed in the objectives, then start to study the
appropriate figures and accompanying tables. Try to construct logical
groupings of muscles that perform the same action. This will ease your
load.
Some clarifications:
1. You do not have to know all of the specific muscles of the erector
spinae; just remember it as one muscle with three parts: the lateral
iliocostalis group, the intermediate longissimus group, and the
medial spinalis group.
2. Some muscles are noted several times because they produce actions
at more than one joint (e.g., psoas major). Muscles that act on the
axial skeleton are particularly likely to fall into this category.
The other tip I give you is to make your own muscle flashcards.
True, there are very attractive commercial alternatives and even computer
software that will help you rehearse. But the advantages to making your
own are several. First, I believe you will learn a great deal from the act of
making your own flashcards; you get that extra mental rehearsal when you
construct your own flashcards. Second, it is a lot cheaper to make your
own flashcards. All you need are some index cards. Third, you can pass
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them down to your children when they come of age. (Just kidding on the
last advantage.)
Begin by listing the name of the muscle in the top left corner of the
index card. Then, write down the actions and attachments (origin,
insertion) of the muscle under the name. Leave a little room on the left
margin. This is where I write down the number of actions for the muscle.
Then, when I quiz myself, I can cover over the actions and know that I
must come up with one, two, three or more actions. Remember
attachments in general.
Let us try an example for the biceps brachii muscle. If you look up
the muscle, you will find that it has two primary actions (flexion of the
forearm, and supination), two origins and one insertion. Hence, I would
write the number "2" in the left margin for two actions to remember. For
our purposes, the general attachments to remember are scapula
(origin) to forearm/radius (insertion). You do not need to remember the
specific landmarks for attachments on bones. When it comes time to
study, I cover everything on the card except the name of the muscle and
the number I placed in the left margin. In this case, I know I must name
two actions.
Remember to identify the muscle as well on Figure 11.7. I could
always ask you facts about the muscle's location. For the biceps femoris I
could ask: "Is the muscle located on the posterior surface of the thigh?" "Is
the muscle superficial or deep?" "Is the muscle found in the lower
extremity?" or "Is the biceps femoris seen on a superficial view of the
posterior thigh?"
With regard to actions, think first mostly in terms of angular
motions (flexion/extension and abduction/adduction) or rotation; or
hybrids of angular movements or rotation (dorsiflexion, pronation, etc.).
Hint: You will only find significant rotation at ball-and-socket and pivot
joints. Another hint: The actions of the muscles that move the foot are
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determined by where each muscle's tendon passes the ankle (those of the
anterior compartment dorsiflex; those of the lateral and posterior
compartments plantarflex). Third study hint: Try to get a sense for
whether a muscle is deep, intermediate, or superficial, relative to other
muscles. This exercise will make subsequent identification of muscles
considerably easier. Remember your self-tests; all it takes is a photocopy
and discipline. Final hint: As a general rule of thumb, in the anatomical
position, muscles on the anterior parts of the neck, arms, forearms, chest,
and abdomen are flexors. Muscles on the anterior aspect of the thigh are
extensors (of the knee). Muscles on the posterior aspect of the neck, arms,
forearms, back, and buttocks are extensors. Muscles on the posterior
portion of the thigh are flexors. (Some muscles act on more than one joint:
take special note of these as well.)
Sample Questions
1. Name the muscle from the list below that is antagonistic to plantor flexion of the foot. a. peroneus brevis b. soleus c. tibialis anterior d. flexor hallucis longus
2. What is the name of a muscle that performs the desired action?
a. antagonist b. agonist c. synergist d. fixator
3. What is the primary action of the palmar interossei?
a. adduct digits b. flex digits c. abduct digits d. extend digits
4. This muscle turns the palm upward or anterior.
a. fibialis anterior b. plantaris
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c. adductor longus d. supinator
5. Which muscle below is not innervated by the obturator nerve?
a. sartorius b. adductor longus c. gracilis d. adductor magnus
Answers to Sample Questions
1. c; 2. b; 3. a; 4. d; 5. a
Written Assignment #4
Instructions
Instructions for submitting assignments electronically in the ICON
Drop Box are posted on the ICON course site under "Submit
Assignments."
Description
This assignment is worth 10 points.
1. Identify muscles that produce flexion at the hip and their
antagonists. Identify muscles that produce abduction at the hip and
their antagonists..
2. Identify the lever type (first, second, or third class) in effect in
flexing the leg at the knee. Next, identify agonists and antagonists
to flexion of the knee.
Examination #2
Examination #2 follows written assignment #4. This will be a one-
hour, supervised examination. No books, notes, or other aids may be
brought to the exam. The examination consists of forty multiple-choice
questions of the same type you have seen in the sections of sample
questions in each lesson. The exam questions are allocated according to
the number of objectives per topic.
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Please read the information regarding exam scheduling and policies
posted on the ICON course Web site carefully. Students with access to the
Internet must use the ICON course Web site to submit exam requests
online. Students who do not have access to the internet may submit the
Examination Request Form located at the back of this Study Guide (print
version only).
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UNIT 4 INTEGRATION
Lesson 12 Nervous Tissue
Lesson 13 Central Nervous System
Lesson 14 Peripheral Nervous System
Written Assignment #5
Lesson 15 Autonomic Nervous System
Written Assignment #6
Lesson 16 Special Senses
Lesson 17 Endocrine System
Examination #3
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Lesson 12 Nervous Tissue
Reading Assignment
Read Chapter 12 in your textbook. As this is the beginning of the
second half of the course, I remind you to use the objectives to guide your
reading.
Objectives
By the end of this lesson, you should be able to:
1. Define peripheral and central nervous systems. List the functions of
the nervous system. Classify spinal cord, brain, spinal nerves and
cranial nerves into either peripheral or central nervous system.
Define and distinguish somatic afferents, somatic efferents, visceral
afferents and visceral efferents (Figure 12.3).
2. Classify gray matter versus white matter in the CNS and PNS:
nerve, nucleus, ganglion, and tract.
3. State the general functions of supporting cells/neuroglial cells:
astrocyte, ependyma, oligodendrocytes, and microglia. See Figure
12.12.
4. Define and describe the general features of a typical neuron.
Include the following: dendrite, axon, cell body (perikaryon),
arachnoid villi, choroid plexus, median aperture, lateral aperture.
Explain the formation of cerebrospinal fluid. Define the different
layers of the meninges: dura mater, arachnoid, and pia mater. See
Figures 13.4b, 13.11, 13.30, and 13.32.
2. Identify the gross features of the cerebrum: hemispheres, corpus
callosum, central sulcus, lateral sulcus, longitudinal fissure,
transverse fissure, cerebral cortex, gyri, and sulci (Figures 13.20).
3. Identify the lobes of the cerebrum and the general functions of each
(Figure 13.23).
4. Describe the three types of white matter in the cerebrum and the
general connections established by each: association fibers,
commissural fibers (corpus callosum), and projection fibers
(internal capsule) (Figure 13.26).
5. Identify the components of the basal ganglia/nuclei and its general
function (Figures 13.21 and 13.27).
6. Discuss the significance of cerebral dominance for language. Also
state implications of damage to the areas involved in language
(Auditory association area, Broca's [motor speech] area, arcuate
fasciculus).
7. Identify the thalamus and state its functions (Figures 13.16, 13.17
and 3.18).
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8. Identify the hypothalamus and state its general functions (Figures
13.16 and 13.19). Also, identify the pituitary gland and
infundibulum (pituitary stalk).
9. Identify the main components of the brainstem and connections
with the cerebellum. Specifically, for the midbrain, state the
functions of the superior colliculi, inferior colliculi, red nucleus,
cerebral peduncle, and substantia nigra. In the pons, state the
functions of the pneumotaxic area, apneustic area, and pontine
nuclei. For the medulla, state the functions of cardiac, vasomotor,
respiratory centers, and the "pyramids." See Figures 13.13 and
13.14.
10. Define the reticular formation in the brainstem and state its
functions (Figure 13.29).
11. Identify the anatomy and the functions of the cerebellum, defining
the components of the cerebellar peduncles (Figure 13.15).
12. Describe the gross features and extent of the spinal cord: cervical
and lumbar enlargements, conus medullaris, filum terminale, and
cauda equina (Figure 13.2).
13. Describe and draw a cross section of the spinal cord identifying:
central canal, white matter, gray matter, anterior, posterior and
lateral horns, anterior, posterior and lateral funiculi, gray
commissure, anterior median fissure, and posterior median sulcus
(Figure 13.4 and 13.5).
14. Know general function and location of sensory and motor tracts in
the spinal cord (see Tables 13.6, 13.7, Figure 13.34).
15. Know these clinical applications: effects of spinal cord section at the
level of the cervical enlargement and between cervical and lumbar
enlargements; stroke.
16. Locate the limbic system and define its functions (13.28).
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Discussion
Read Chapter 13 to get oriented. You should know that the brain is
comprised of four parts: the cerebrum, brain stem, diencephalon, and
cerebellum. The entire central nervous system (CNS) is protected by the
meninges.
Three layers of meninges cover and protect the entire CNS. They are
comprised of: an outer tough layer—dura mater; a middle layer—
arachnoid; and an inner, delicate membrane that adheres directly to the
spinal cord and brain—pia mater. The subarachnoid space contains the
cerebral spinal fluid (CSF). This fluid helps protect the spinal cord by
providing a fluid shock absorber to dissipate external blows to the
vertebral column. You can see all of these meningeal structures in Figures
13.4b, 13.11, 13.30 and 13.32.
You should also recognize the dura mater, arachnoid, and pia mater
also cover the brain. These coverings continue throughout the CNS. Figure
13.11 identifies ventricles that are part of the cerebrospinal fluid (CSF)
circulation system. CSF is produced by capillary networks called choroid
plexuses, located in each of the four major ventricles (two lateral, a third
and a fourth).
Three apertures (one median, two lateral) in the fourth ventricle
give CSF access to the subarachnoid space. The CSF moves from the
ventricles into the subarachnoid space and then is returned to the venous
system by dural sinuses (see Figure 13.30). A dural sinus is a venous
channel running through the dura mater. Notice in Figure 13.30a that the
superiorly-directed projections push through the sinus as arachnoid villi
(villus is singular). The arachnoid villi are responsible for returning the
CSF back into the bloodstream. Therefore, CSF circulation begins in the
choroid plexuses of each ventricle where CSF is produced. The CSF finds
its way into the subarachnoid space via one of the three apertures (Figure
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13.11). After a time, the CSF is returned to the bloodstream by way of one
of the arachnoid villi associated with the superior saggital sinus (Figure
13.30).
The cerebrum is the part of the brain most people think about or
picture when the word brain is used. Like the rest of the CNS, the
cerebrum is comprised of gray matter and white matter, except it is
arranged in a fashion just the reverse of that in the spinal cord. The gray
matter (cell bodies mostly) is situated on the outside of the cerebrum; this
area is referred to as the cortex (see Figure 13.23). Study the cerebrum in
Figure 13.20 to identify the structures listed in Objective two.
The white matter (primarily myelinated axons) of the cerebrum is
underneath (deep to) the cortex. It contains three kinds of fibers (axons).
Association fibers connect different lobes on the same hemisphere.
Projection fibers include those axons from the thalamus (by way of the
internal capsule) on their way to the cortex. Projection fibers also include
fibers (axons) from cell bodies in the cortex on their way to the internal
capsule. Some of the projection fibers directed inferiorly eventually
become some of the descending tracts (the corticospinal tracts for
instance). The last type of fiber in the white matter of the cerebrum is
called a commissural fiber. Commissures connect the two hemispheres of
the cerebrum. Study Figure 13.26 to get a sense of what areas the axons of
the white matter of the cerebrum connect. There are anterior and posterior
commissures as well as the largest commissure—corpus callosum. Corpus
callosum is labeled in Figure 13.26.
Figure 13.23 displays a functional map of the cerebral cortex. Be
able to define the general functions of each lobe of the cerebrum. To make
your task a little easier, note that motor areas are confined to the frontal
lobe, whereas sensory areas are found on temporal, parietal, and occipital
lobes. Below is a matching exercise to test your recall after you have
studied the cortical areas of the cerebrum for a while.
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Identify one correct answer for each question.
a. frontal lobe b. temporal lobe c. occipital lobe d. parietal lobe
1. Receives sensory impulses from the eyes and interprets shape and color. 2. This area of the brain receives sensory information from cutaneous,
muscular, and visceral receptors from various parts of the body. 3. Controls voluntary movements of the eye. 4. Controls muscles of speech by translating thoughts into speech. 5. Voluntary control of skeletal muscle, usually on the opposite side of the
body.
Read on for the answers.
The basal nuclei represent a loose coalition of separate nuclei
controlling gross subconscious movements and muscle tone. Swinging of
the arms while walking and contraction of proximal limb musculature in
fundamental movement patterns (e.g., walking, throwing, etc.) are
controlled by the basal nuclei. The basal nuclei are also responsible for
starting and stopping movements. Some instructors liken the basal nuclei
to a "filtering" system because the characteristic sign of dysfunction of the
basal nuclei is involuntary (unwanted) movement (dyskinesia)—as in
Parkinson's disease. If the filter was working, the involuntary movements
would not sneak through.
Identify the parts of the basal ganglia/nuclei (caudate, lentiform
nuclei claustrum) in Figures 13.21 and 13.27. With the substantia nigra
(not pictured), these are major structures in the basal nuclei. (The answers
to the matching exercise are 1. c, 2. d, 3. a, 4. a, and 5. a.)
Proficiency with language, such as understanding the written and
spoken word and speech, are controlled by the so-called dominant cerebral
hemisphere. For most people, the dominant cerebral hemisphere is the
left. (Since cerebral control of the body is contralateral, the dominant
hemisphere usually is associated with the dominant or preferred hand).
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The auditory association area (see Figure 13.23) on the temporal lobe
receives and interprets auditory information (speech comprehension).
Association fibers (the arcuate fasciculus) connect the auditory association
area with the Broca's (motor speech) area on the frontal lobe. This allows
us to hear a question in class, and verbalize an answer to the question.
Damage to any of these structures will result in aphasia (difficulty
using and/or understanding written or spoken language). Note that
aphasia results only when there is damage to one of these areas on the
dominant cerebral hemisphere. This makes language unique because
most other cerebral functions are bi-lateral.
The thalamus is an aggregation of gray matter (nuclei) at the end of
the brainstem; the thalamus is the "gateway" to the cerebral cortex (see
Figures 13.16 and 13.18). Ascending (sensory) tracts travel superiorly
through the spinal cord, then continue on through the brainstem. Hence,
the thalamus relays most types of sensory information (except smell) to
the cerebral cortex via a thick band of fibers (axons), called the internal
capsule (see Figure 13.17b), from the thalamic nuclei.
Below the thalamus (see Figures 13.16 and 13.19) one finds a second
group of nuclei, called the hypothalamus. "Hypo" ("less than" or "under")
suggests the location of these nuclei, directly under the thalamus. The
hypothalamus has several major functions you should remember. It plays
a role in the autonomic nervous system as its major control center. The
hypothalamus also influences the endocrine system through its
communication with the pituitary gland via the infundibulum (pituitary
stalk), illustrated in Figures 13.16 and 13.19 (which we will study more in
the endocrine lesson). There are certain cyclical centers for hunger, thirst,
and sleep patterns. Body temperature is also regulated by hypothalamic
nuclei.
Together the hypothalamus and thalamus are called the
diencephalon.
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The continuation of the spinal cord upward is the brainstem (see
Figures 13.13 and 13.14). The brainstem lies on the ventral or basal surface
of the brain.
All of the parts of the brainstem share several major functions:
1. They act as a conduit for the ascending or descending tracts (in
other words, the brainstem connects the spinal cord to the rest of
the brain and parts of the brain with one another).
2. They house many of the cranial nerve nuclei.
3. They are the home for several other important nuclei, including the
reticular formation (discussed at some length below).
You should know that the brainstem is composed of three parts:
medulla, pons, and midbrain. Each has a connection with the cerebellum.
(Identify the cerebellum in Figure 13.15.). The connections are called
peduncles. The medulla, pons, and midbrain connect with the cerebellum
via inferior, middle, and superior cerebellar peduncles, respectively
(Figure 13.13c).
You should also know the following about each part of the
brainstem:
1. The medulla contains many important "centers" (Figure 13.14) for
vital functions (cardiac rhythm, respiratory rhythm, and blood
pressure). This is why damage to the medulla is often fatal. The
medulla also contains nuclei for cranial nerves 8, 9, 10, 11, and 12.
(Number 8 is shared with the pons.) The medulla is connected with
the cerebellum by the inferior cerebellar peduncle. See Figure
13.13c. The pyramids of the medulla carry motor fibers that
originate in the frontal lobe of the cerebrum, destined for the spinal
cord.
2. The pons also contains several cranial nerve nuclei and pontine
nuclei. The latter send axons to the cerebellum via the middle
cerebellar peduncle. See Figure 13.14. The pons contains nuclei for
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cranial nerves 5, 6, 7, and 8. The pons also helps regulate
respiration through apneustic and pneumotaxic centers.
3. The midbrain, likewise, contains nuclei for cranial nerves as well as
the red nucleus, substantia nigra, and corpora quadrigemina. The
red nucleus is the origin of the rubrospinal tract. The nuclei of the
superior and inferior colliculi serve as the origins for fibers that will
eventually become the tectospinal tract. The substantia nigra joins
several other widely separated nuclei to form a functional unit
called the basal nuclei. The midbrain also houses nuclei for the
third and fourth cranial nerves. See Figure 13.14.
Throughout the brainstem is another poorly organized collection of
nuclei called the reticular formation (see Figure 13.29). The reticular
formation is vital to our general level of alertness and attention. This is
why the reticular formation is sometimes called the reticular activating
system. The reticular formation also plays a role in controlling muscle tone
through its several reticulospinal tracts.
As you can probably tell by now, the cerebrum does not work alone.
We have already identified other parts of the brain, the thalamus and basal
ganglia especially, that play major roles in coordinating things. We need to
add the cerebellum to that list now.
Identify the cerebellum in Figure 13.15. Histologically, the
cerebellum is arranged in a fashion similar to the cerebrum, with cell
bodies (gray matter) on the outside and fibers (white matter) on the
inside. We already noted the cerebellum has three attachments
(peduncles), one with each part of the brainstem (see Figure 13.13c).
Through some of these peduncles, the cerebellum can send axons to
influence and help other parts of the brain do their jobs better.
The cerebellum is primarily a motor coordination center. This
means the cerebellum checks movements as they occur, to assure they are
carried off as planned, so the entire movement appears as one smooth
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whole. If a movement "error" is detected, then the cerebellum alerts other
parts of the brain, so the movement can be corrected. When things go
wrong with the cerebellum, you will sometimes observe a decomposition
of movements, movements which begin to appear short, choppy, and
uncoordinated—a conditions known as ataxia (uncoordinated movement).
The cerebellum is also concerned with control of postural muscles
and equilibrium. Along with its coordination functions, the cerebellum
does all of these tasks at the subconscious level. This is very useful because
it frees up attention and cerebral capacity to think about things far more
interesting than contracting the right muscles so that we can stand or sit
erect. The cerebellum makes life a lot more interesting because it takes
care of almost all of the tedious "work" without having to occupy a lot of
our conscious attention.
You should have a general familiarity with the components of each
of the three peduncles that connect the cerebellum to each part of the
brainstem. The inferior peduncle carries proprioceptive (joint sense)
sensation to the cerebellum. The middle peduncle carries fibers from the
pons to the cerebellum. The superior peduncle carries fibers to the red
nucleus from the cerebellum.
The spinal cord is primarily a pathway for nervous impulses to and
from the brain. It also performs a few simple, protective functions (called
spinal reflexes) on its own. Nevertheless, you should remember that
neurons in the spinal cord are largely under the control of neurons
residing in the brain. This is why some neurons in the spinal cord are
referred to as lower motor neurons (and those in the brain as upper motor
neurons).
Recall that the spinal cord and the remainder of the CNS is
comprised of white matter and gray matter. The gray matter marks the
location of nerve cell bodies and appears as a darker hue because the cell
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bodies of neurons are not myelinated. White matter is made up of
myelinated nerve cell processes—axons and dendrites.
The general features of the spinal cord are illustrated in Figure 13.2.
The spinal cord begins at the foramen magnum (of the occipital bone) and
ends at the level of upper lumbar vertebrae in a tapered structure called
conus medullaris. Inspect the length of the spinal cord proper and note
that it is not of uniform thickness throughout its entire length. Two areas
in particular are wider; they are called the cervical and lumbar
enlargements. What do you think accounts for these enlargements?
Filum terminale arises from the conus medullaris and anchors to
the coccyx. The filum terminale is not nervous tissue. It is, more or less, a
ligament that helps to secure and stabilize the spinal cord in the vertebral
canal. Filum terminale is found in amongst a series of fibers called cauda
equina.
Cauda equina is comprised of nervous tissue. Because the spinal
cord does not extend the entire length of the vertebral column, some nerve
fibers—those in the lumbar, sacral, and coccygeal regions specifically—
must travel inferiorly for a distance to exit at the appropriate vertebral
level. For example, the S1 spinal nerve will exit at the S1 vertebral level,
even though the spinal cord proper ends at about L2. To do this, S1 fibers
must travel downward until they arrive at the appropriate vertebral level.
This effect for lumbar and sacral spinal nerves results in the cauda equina.
Figures 13.4 and 13.5 shows the spinal cord in cross section. The
gray matter, where all the cell bodies are, forms an H-shaped
configuration in the center of the cord. Around the gray matter is white
matter, composed largely of myelinated axons. A gray commissure forms
the horizontal bar of the H in the gray matter. The H-shaped pattern is
also further subdivided into horns, two anterior, two posterior. The white
matter is likewise subdivided into anterior, lateral and posterior funiculi.
The word "funiculus" is used because the white matter contains bundles of
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myelinated axons carrying information up to or down from the brain. Soon
you will learn that each of the funiculi is further subdivided into ascending
or descending tracts. The ascending tracts are carrying sensory
information to the brain; the descending tracts are carrying motor
information to the spinal cord. (It is a good idea to test yourself on Figure
13.5; remember, part of the objective is to draw a cross section of the
spinal cord, too.)
The cell bodies of motor neurons are located in the anterior gray
horn of the spinal cord. The cell bodies of sensory neurons are located in
structures called a dorsal root ganglia—as a cluster of cell bodies in the
PNS. See Figure 13.5.
Just as nerves are white matter in the PNS, tracts are the white
matter in the CNS. Tracts, as we saw before, were defined as columns or
bundles of axons traveling up (ascending tracts) or down (descending
tracts) the spinal cord, to or from the brain. As it so happens, the
organization of tracts is not haphazard, but rather systematic. Axons
carrying similar kinds of impulses (or information) tend to group together
so that we may identify specific tracts carrying specific kinds of
information (sensory or motor). Study Tables 13.6 and 13.7 and Figure
13.34. You should know all sensory (ascending) tracts and motor
(descending) tracts, where they are located in the spinal white matter, and,
generally, what kind of functions they perform. You do not have to know
the reticulospinal tracts.
Many of the tracts are named for where they begin and end, so this
should make your task easier. For instance, the lateral spino-thalmic tract
is located in the lateral white matter of the spinal cord and carries
information from the spinal cord ("spino") to the thalamus ("thalamic") in
the brain. Even if you could not remember that it is an ascending tract, you
could deduce that it is an ascending tract from the name. Likewise,
spinocerebellar tracts go to the cerebellum from the spinal cord. And
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corticospinal tracts go from the cerebral cortex to the spinal cord (anterior
and lateral give locations of the corticospinal tracts in the white matter). It
might be a good idea to test yourself on the function of each tract by
developing a matching exercise. Put the tracts on one side and the
functions on the other, then try and match them up.
Injuries to the CNS are very serious and, too often, permanent.
Trauma to the spinal cord is usually from an external event—such as a
vehicular accident. Although, many different types of injuries may result.
Two of the most common result in paraplegia and quadriplegia. Severing
the spinal cord between cervical and lumbar enlargements denies
voluntary control to both lower extremities. Severing the spinal cord at the
cervical enlargement means that all four extremities are involved—
quadriplegia.
A cerebral vascular accident (CVA) or stroke is a form of brain
injury, making it similar in some respects to any brain trauma except for
etiology. The majority of strokes cause injury by depriving brain tissue of
blood supply (ischemia). In contrast, brain trauma may result from direct
injury to brain tissue, or more commonly, put pressure on brain tissue as a
result of a blood clot (hematoma) associated with damage to meningeal
blood vessels.
In either case, the symptoms are correlated with the extent of injury
and the nature of the damaged tissue. For example, CVAs that affect the
internal capsule (projection fibers) on one side often result in partial or
complete paralysis on the opposite side of the body (contralateral
hemiphagia). Furthermore, strokes to the dominant hemisphere
frequently result in difficulty using or understanding language (aphasia).
Cerebral palsy results when some event causes the fetal brain to be
deprived of an adequate oxygen supply before birth. Hence, cerebral palsy
is a congenital brain injury (in contrast to strokes and traumatic brain
injuries which are acquired). Cerebral palsy most commonly affects motor
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areas of the cerebral cortex, but may affect the basal nuclei or the
cerebellum. Symptoms manifest as syndromes of motor impairments,
such as spasticity of control, disruption of muscle tone and function,
ataxia, and other motor dysfunction
The limbic system is illustrated in Figure 13.28. It is generally
regarded as the primitive brain and comprised of nuclei that surround the
brainstem—primarily the amygdaloid nucleus, fornix, hippocampus, and
cingulate gyrus. The limbic system is primarily involved in primitive
emotions and, surprisingly, memory. Several structures in the limbic
system are subject to considerable research effort because deterioration of
some of the nuclei is associated with one type of senility/dementia
(Alzheimer's disease). Note also the involvement of the olfactory nerve in
the limbic system—a basis for the ability of perfume and after-shave to
provoke sex-drive.
Sample Questions
1. This structure serves as a relay for sensory information bound for the cerebral cortex. a. cerebellum b. thalamus c. midbrain d. basal ganglia
2. An obstruction in an interventricular foramen would interfere with
flow of CSF into this space. a. lateral ventricle b. third ventricle c. fourth ventricle d. median aperture
3. This lobe of the brain is responsible for controlling voluntary motor
activity. a. frontal lobe b. parietal lobe c. occipital lobe d. temporal lobe
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4. The pons is connected to the cerebellum by this band of white matter.
a. superior cerebellar peduncle b. decussation of pyramids c. tentorium cerebelli d. middle cerebellar peduncle
5. The vital centers for control of respiration, heart rate, and blood
pressure are located here. a. spinal cord b. medulla c. cerebrum d. cerebellum
Answers to Sample Questions
1. b; 2. b; 3. a; 4. d; 5. b
Go on to Lesson 14.
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Lesson 14 Peripheral Nervous System
Reading Assignment
Read Chapter 14 in your textbook. As always, study the figures
thoroughly and let the objectives guide your reading.
Objectives
By the end of this lesson, you should be able to:
1. List all twelve cranial nerves and the part of the brain or brainstem
associated with each. Briefly, describe the structures innervated by
each. Classify cranial nerves as primarily sensory, primarily motor,
or mixed. (See Tables 14.2, 14.3, and Table 2 in the Discussion
section of this lesson.) Also name the 31 pairs of spinal nerves
(Figure 14.6)
2. Describe the typical spinal nerve (see Figures 14.2 and 14.7), its
dorsal and ventral roots, and its dorsal and ventral rami. Discuss
the relationship between ventral rami and intercostal nerves and
plexuses. Identify body regions innervated by nerves from each
plexus.
3. Describe the concept of a plexus. Identify ventral rami of spinal
nerves that contribute to each plexus (see Figures 14.8–14.13 and
Tables 14.4–14.7). Know which plexus each of the following nerves
arise from and the muscular innervations of each nerve and plexus:
monitors blood pressure 10. vagus swallows, tastes, some motor to
muscles of speech, parasympathetic, most of the ventral body cavity (viscera)
11. accessory turns the head (sternocleidomastoid muscle) and shrugs the shoulder (trapezius) muscles
12. hypoglossal moves the tongue
Next, consider Figures 14.2 and 14.7. The diagrams portray a spinal
nerve from formation to division into two branches, called rami. Spinal
nerves are formed when two roots, one ventral and one dorsal, come
together. The ventral root is motor; the dorsal root is sensory. Once the
two roots have jointed, you have a spinal nerve. From this point on, the
nerve is also considered a mixed nerve, mixed in the sense that it has
both sensory and motor components (fibers). After spinal nerves have
exited the intervertebral foramina, they split—one branch going forward,
one backward. These branches have names: the first is the ventral ramus,
the other one is the dorsal ramus. Do you think the rami are motor only,
sensory only, or mixed?
Dorsal rami innervate the muscles of the deep back (e.g., erector
spinae) and provide sensory innervation to the back. Verntral rami can do
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one of two things. They either become intercostal (between the ribs)
nerves or they enter into plexuses. There are four major plexuses.
A plexus is a network of nerves that begins with ventral rami. They
combine and recombine and eventually result in distinct nerves. Study of
Tables 14.4 through 14.7 and Figures 14.8 through 14.13. Identify muscle
groups innervated by each plexus (e.g., nerves from the brachial plexus
innervate muscles of the shoulder girdle and upper extremity and provide
sensory/cutaneous innervation of the upper extremity). Next, identify
muscle groups innervated by specific nerves and plexuses listed in
Objective #3. For example, the radial nerve innervates muscles of the
posterior arm and forearm (these muscles generally extend the forearm,
wrist, and digits).
Study each plexus and note the ventral rami of spinal nerves that
contribute to each. An unfortunate convention is that the ventral rami that
contribute to the formation of a plexus are called roots. The word "roots"
here does not refer to ventral and dorsal roots that combine to form spinal
nerves. Note—you do have to remember the nerves that arise from the
plexuses. (By the way—the answer to the question posed a couple of
paragraphs above is that ventral and dorsal rami are mixed. Any nerve
peripheral to the intervertebral foramen is mixed.)
To summarize, the cervical plexus is formed by ventral rami of
spinal nerve C1–5. The brachial plexus receives contributions from ventral
rami of C5–T1. The lumbar plexus is formed from spinal nerves L1–L4. L4
overlaps into the sacral plexus, which receives contributions from L4–S4
spinal segments. Remember to identify the nerves in Objective #3 and the
plexus of origin for each.
I have attempted to summarize and simplify nervous innervations
in Table 2.
Table 2. Nervous Innervations
Nerve Area
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Nerve Area Dorsal Rami Muscles of the deep back Phrenic Diaphragm Intercostals Intercostal muscles, muscles of the abdominal
wall Pectoral nerves Pectoral muscles Dorsal Scapular Rhomboids and levator scapulae Suprascapular Supraspinatus, Infraspinatus Thoracodorsal Latissimus dorsi Long Thoracic Serratus anterior Axillary Deltoid, Teres minor Ulnar 1½ muscles of the anterior forearm and intrinsic
muscles of the hand (all digits except thumb) Subscapular Subscapularis, Teres major Radial (includes branches
that become posterior interosseous nerve)
Muscles of the posterior arm and forearm
Musculocutaneous Muscles of the anterior arm Median Muscles of the anterior forearm and thumb Femoral Muscles of the anterior thigh Obturator Muscles of the medial thigh Inferior gluteal Gluteal muscles Superior gluteal Gluteal muscles Tibial (includes sciatic
innervations) Muscles of the posterior thigh and leg
Peroneal (fibular nerve) Muscles of the lateral and anterior leg Pudendal Perineum (floor of pelvis)
The fourth objective asks you to trace a nerve impulse from spinal
cord to brachialis muscle. If you understand this pathway, you should be
able to trace a nerve impulse from the spinal cord to any of the muscles
you learned in the muscle system lesson. The pathway to the brachialis
muscle is as follows:
Anterior gray horn of spinal segments C5–T1 to anterior roots of
spinal nerves C5–T1 to join posterior roots of spinal nerves C5–T1 to form
spinal nerves C5–T1 to ventral rami of spinal nerves C5–T1 to form "roots"
of brachial plexus. The impulse then negotiates trunks–divisions–cords of
the plexus to eventually form five terminal nerves of the brachial plexus
(among these is the musculocutaneous nerve, which innervates the
Brachialis muscle).
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As you might surmise, spinal cord damage is far more serious than
trauma to a single peripheral nerve. With the latter, only the muscles and
skin innervated by the damaged nerve will be affected. Review the clinical
applications in Chapter 14 that describe the motor impairment that would
result if median, ulnar, radial, femoral, tibial, or peroneal (fibular) were
damaged. Even if the damaged nerve is a major one, the extent of the
symptoms will be far less than with a spinal cord injury. Furthermore, a
severed peripheral nerve is likely to repair itself, whereas the spinal cord
does not.
Sensory fibers are attached to receptors of various kinds. In
particular, a map of innervation by sensory fibers has been developed on
the surface of the body. Each segment of the spinal cord is responsible,
through its sensory fibers, for supplying a part of the surface of the body.
The skin supplied by the spinal cord segment is referred to as a
dermatome. Dermatomes can be used to determine the extent of spinal
cord injury. A map of the dermatomes is shown in Figure 14.14.
Sample Questions
1. Which of the following is composed of sensory fibers only? a. ventral roots of spinal nerves b. ventral rami of spinal nerves c. dorsal roots of spinal nerves d. dorsal rami of spinal nerves
2. What is the name given to a collection of nerve cell bodies outside the
CNS? a. ganglion b. horn c. tract d. nucleus
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3. How many pairs of cervical spinal nerves are there? a. 5 b. 8 c. 10 d. 12
4. Identify the nerve injured if a patient is unable to move his thumb.
a. ulnar b. median c. axillary d. radial
5. The phenic nerve develops from this plexus.
a. sacral b. lumbar c. brachial d. cervical
Answers to Sample Questions
1. c; 2. a; 3. b; 4. b; 5. d
Written Assignment #5
Instructions
Instructions for submitting assignments electronically in the ICON
Drop Box are posted on the ICON course site under "Submit
Assignments."
Description
This assignment is worth 10 points.
1. Trace a nervous impulse from the spinal cord to the rectus femoris
muscle, noting different nervous tissue structures the impulse will
have to negotiate along the way. (A couple of tips: you will have to
start by looking up, in Chapter 11, the nerve that innervates the
rectus femoris muscle. Start at the anterior gray horn of the spinal
cord; then trace the impulse out the intervertebral foremen and
through the appropriate plexus.)
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2. Define a nerve plexus. List spinal nerves that contribute to the
formation of the four major plexuses. Generally, describe muscle
groups innervated by nerves from each of the plexuses. Identify the
anatomical location where each plexus is found.
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Lesson 15 Autonomic Nervous System
Reading Assignment
Let the objectives guide your reading of Chapter 15 in your
textbook. There is a lot more information in the chapter than you are
required to know, but do make sure to give the chapter at least one
complete reading.
Objectives
By the end of this lesson, you should be able to:
1. Contrast autonomic and somatic systems (see Figure 15.2). Define
anatomical differences between sympathetic and parasympathetic
divisions of the autonomic nervous system (see Table 15.1).
2. Locate ganglia for the ANS: pre-vertebral (peripheral) ganglia,
sympathetic trunk, and terminal ganglia (Figures 15.5 and 15.7).
3. Locate the adrenal medulla (Figure 15.7) and explain its
relationship to the ANS.
4. Describe the possible fates of pre-ganglionic sympathetic axons.
Define white and gray rami communicans (see Figures 15.9–15.13).
5. Know the general effects of sympathetic and parasympathetic
innervation of visceral effectors listed on Table 15.2.
6. List "higher centers" that influence the autonomic nervous system.
7. Describe the role and location of visceral sensory/afferent neurons.
Define referred pain.
Discussion
Much of what you have to accomplish relates to comparing the
autonomic nervous system (ANS) to the somatic system and comparing
the two components of the ANS to one another. We will begin by
comparing the ANS to the somatic system.
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If you recall, the somatic motor system is responsible for
innervation for voluntary muscle (skeletal muscle). By contrast, the ANS is
responsible for innervation of involuntary muscle (smooth and cardiac
muscle). The somatic system is a one neuron system. That is, an axon from
a motor neuron cell body (located in the anterior gray horn of the spinal
cord) travels directly to the muscle it is to innervate before forming a
neuromuscular junction with the muscle cell. The ANS is a two neuron
motor system. The first neuron cell body is located in the central nervous
system. An axon from the first neuron synapses on the second neuron in a
peripheral ganglion; then an axon from the second neuron proceeds to the
muscle to be innervated. Some of these differences are illustrated in Figure
15.2
Another difference between the somatic system and ANS is that the
neurotransmitter substances differ. The transmitter substance for the
somatic system is always acetylcholine (ACh). The transmitter for the ANS
can either be ACh or norepinephrine. Lastly, somatic stimulation is always
excitatory; ANS innervation may lead to excitation or inhibition of the
involuntary muscle.
Now study Figures 15.5 and 15.7 and Table 15.1 for graphic and
verbal summary of the differences between the sympathetic and
parasympathetic divisions of the ANS. Note the following key differences:
1. origin of the preganglionic neurons for each division and 2. location of
the peripheral ganglia for each division. In sum, a pathway within the ANS
will have three components: preganglionic neurons, autonomic ganglia
and postganglionic neurons, and effectors (involuntary muscle).
Part of the adrenal gland, the adrenal medulla, can be included in
the sympathetic division of the ANS. The adrenal medulla secretes
epinephrine (and norepinephrine) into the bloodstream with effects
almost identical to sympathetic stimulation. The widespread activation of
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a sympathetic response is partly attributable to the rapid distribution of
hormones from the adrenal medulla in the bloodstream.
Now let's briefly take a closer look at the location of the ganglia in
each division. Return to Figures 15.5 and 15.7. Note that sympathetic
ganglia lie in one of two places. They are either close to the spinal cord in a
structure called the sympathetic trunk (alongside the vertebral column)
but a few are located peripherally, in front of the vertebral column (and
the CNS). The latter are referred to as pre-vertebral (peripheral) ganglia.
Regardless, sympathetic ganglia are relatively close to the vertebral
column (and the CNS). Examine Figure 15.7 to confirm this point. Notice
that the ganglia for the parasympathetic division (called terminal ganglia)
are almost all situated on or close to the structure to be innervated, quite
distant from the CNS.
We earlier noted that the two divisions employed different
transmitter substances. Specifically, the parasympathetic division uses
only ACh as a transmitter substance. The sympathetic division's
transmitter substance will vary depending on whether the synapse is
between preganglionic axon and postganglionic neuron or between
postganglionic axon and involuntary muscle. In the case of the former, the
transmitter substance is also ACh. But with the second synapse
(neuromuscular junction) the transmitter substance is almost always
norepinephrine. ("Almost" because there are a few exceptions where the
transmitter substance at the sympathetic division's postganglionic
neuron's synapse with the smooth or cardiac muscle is also ACh.) Figure
15.4 summarizes transmitter substance similarities and differences
between the two divisions.
For most organs and viscera, the ANS supplies dual innervation.
That is both sympathetic and parasympathetic divisions innervate
effectors. The result of dual innervation could be antagonistic (opposite) to
one another, complementary, or cooperative.
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Figures 15.9–15.13 illustrate the three possible fates of
preganglionic sympathetic axons. They can do any of the following:
1. Synapse on the sympathetic trunk and be distributed with a spinal
nerve at the same spinal segment;
2. Synapse at a higher or lower level of the sympathetic trunk and be
distributed with a spinal nerve at a different spinal segment; or
3. Pass through the sympathetic trunk and become a splanchnic nerve
to one of the three peripheral ganglia anterior to the vertebral
column (e.g., celiac). See Figure 15.7.
When you are comfortable with the materials we have covered so
far, turn to Table 15.2. Objective five requires you to know the general
effects for the sympathetic and parasympathetic stimulation. If you look
over Table 15.2 a couple of times, you should get the sense that the
sympathetic division usually produces a response in the organ or structure
innervated consistent with meeting an emergency. Conversely, the
parasympathetic division almost always results in a rest and recovery
response in the structure innervated. These general effects are consistent
with the primary purposes of each division. The sympathetic division is
concerned with responses to emergency situations, often called the "fight
or flight response." Energies and resources within the body are mobilized
for action. In contrast, the parasympathetic division seeks to conserve
energy and take care of routine, but necessary, "housekeeping" chores that
must be done for the body to function properly on a day-to-day basis.
Hence, if you think of what you would want the organ to be doing in an
emergency, you will usually be able to deduce the sympathetic effect on the
organ. The parasympathetic effect is generally the opposite, or it has no
effect on the organ or tissue.
Higher control of the ANS is exerted mostly through the
hypothalamus, reticular formation in the brainstem, and control centers in
the medulla oblongata, but several other structures have lesser effects. The
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anterior nucleus of the thalamus and the cerebral cortex can have some
effect on the ANS.
Although the majority of discussion of the ANS features its visceral
motor functions, visceral sensory neurons do exist and it is clear we can
feel some modalities in visceral structures (especially temperature and
pain). However, unlike the clear anatomical differences between visceral
motor neurons, it turns out that visceral sensory neurons are found in the
same location as somatic sensory neurons—in the dorsal root ganglia. One
notable difference between somatic sensory and visceral sensory systems
does exist: the concept of referred pain. Whereas pain associated with
somatic sensory receptors is projected to its actual physical location (e.g.,
pain from a cut finger), with the visceral sensory system it is projected to
an area of the body that does not always correspond to the visceral organ
(e.g., pain associated with a heart attack). (See Figure 15.15.)
Sample Questions
Try these after you believe you have mastered the material covered
in the objectives.
1. Which statement concerning the ANS is not true? a. It usually operates without conscious control. b. It regulates visceral activities. c. All of its axons are afferent (sensory) fibers. d. It contains ganglia.
2. Control of the ANS is exerted by all but which of the following?
a. medulla oblongata b. hypothalamus c. filum terminale d. thalamus
3. Axons from preganglionic neurons of the parasympathetic division of
the ANS synapse here. a. sympathetic chain ganglia b. peripheral ganglia c. terminal ganglia
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d. dorsal root ganglia
4. Which is not part of the fight or flight response? a. dilation of the pupils b. increased heart rate c. constriction of blood vessels in the viscera d. contraction of the urinary bladder
5. Preganglionic fibers of the sympathetic division tend to be shorter than
postganglionic fibers for this reason: a. their ganglia lie closer to the vertebral column. b. they have gray rami communicantes. c. they do not synapse with splanchnic nerves. d. they have to synapse on more postganglionic neurons.
Answers to Sample Questions
1. c; 2. c; 3. c; 4. d; 5. a
Written Assignment #6
Instructions
Instructions for submitting assignments electronically in the ICON
Drop Box are posted on the ICON course site under "Submit
Assignments."
Description
This assignment is worth 10 points.
1. Identify and explain the principle differences between the voluntary
nervous system and autonomic nervous system.
2. Define autonomic ganglion? Describe the location and function of
the three types of autonomic ganglia. Define and discriminate white
and gray rami communicantes.
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Lesson 16 Special Senses
Reading Assignment
Read Caper 16 in your text. Use the objectives below to help identify
important information in the chapter.
Objectives
By the end of this lesson, you should be able to:
1. Contrast general sensory receptors and special sensory receptors.
2. Describe the microscopic anatomy of receptors for taste and smell.
Summarize their neural pathways and the cranial nerves involved.
3. Identify the anatomy of the eye, including lacrimal gland, tunics
6. Summarize the neural pathways for hearing and balance.
Discussion
Special senses, suchas vision and hearing, distinguish themselves
from general sensory receptors on the basis of two main differences. First
of all, general sensory receptors are spread throughout the body—e.g.,
receptors for touch are found everywhere. In contrast special senses are
resticted to the head region. Secondly, special sense information is
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transported by way of cranial nerves, not spinal nerves, as are most
general senses.
Smell and taste are two special senses that are quite old from the
point of view of evolution—most mammals are able to smell and taste. In
fact, in lower species these two modalities are primary methods through
which the creature understands the environment. Taste and smell are
preserved in the human species, but are not as vital to interpretation of the
environment as with lower species.
Smell receptors are located primarily in the upper nasal mucosa
and nasal septum (the cartilage that separates the two nasal cavities).
Figure 16.3 displays olfactory receptors and the formation of the olfactory
nerve (first cranial nerve) from the convergence of olfactory receptor cell
fibers. The olfactory nerve transmits the smell information to the olfactory
cortex (see Figure 13.23b). Of course, the olfactory nerve and smell
information are involved in the primitive limbic system discussed earlier
in this unit.
In contrast, taste is monitored by three cranial nerves—the facial,
glossopharyngeal, and the vagus (cranial nerves 7, 9 and 10 respectively).
However, all three cranial nerves feed taste information into a common
nucleus (the solitary nucleus) in the medulla (see Figure 16.2). From there
taste information has a mandatory synapse on the thalamus and then is
projected to the gustatory cortex on the inferior part of the post-central
gyrus (see Figure 13.23a). As you can observe in Figure 16.2, taste
receptors are embedded in the tongue and pharynx.
Vision is a sensory modality that would be difficult to do without.
Extra-ocular muscles (see Figure 16.6) allow us to voluntarily direct our
gaze in a variety of directions to take in visual-sensory information about
the environment. The anatomy of the eye is provided in Figure 16.7. The
eye is divided into two distinct areas delineated by the anterior and
posterior chambers. The anterior chamber is filled with a fluid substance,
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the aqueous humor. It is produced and drained on an on-going basis.
(Failure to drain enough aqueous humor from the anterior chamber
results in a build-up of pressure that can damage the eye permanently—
glaucoma). In contrast the posterior chamber is filled with a firmer, gel-
like matrix known as the vitreous humor. It is stable and does not need to
be replaced constantly. The vitreous humor gives a stable form and shape
to the eye.
The interior of the eye is lined with three layers or tunics. An outer
fibrous tunic is composed of the sclera posteriorly and the cornea
anteriorly. The anterior cornea is transparent and allows light to pass
through.
The intermediate tunic likewise has an anterior part (the ciliary
body) and a posterior part (the choroid). A part of the ciliary body, the
ciliary zonule, allows the smooth muscle of the ciliary body to adjust the
concavity/convexity of the lens so that light passing through the opening
(the pupil) will strike the sensory receptor for light in the deep tunic (the
retina) and be detected. It is the diameter of the pupil that automatically
adjusts to illumination by constricting or dilating.
The third tunic of the eye is the retina, containing two layers. One of
the layers of the retina contains sensory receptors for light and is called the
neural layer. Fibers from a variety of different types of sensory cells in the
retina pass posteriorly and converge to form the optic nerve (second
cranial nerve). Figure 16.10c shows the fibers converging on the posterior
pole of the eye to form the optic nerve.
Figure 16.15 illustrates the pathway for light information from the
retina to the visual cortex of the occipital lobe of the cerebral cortex.
Objective four lists the structures of the visual pathway in correct order.
You should remember these structures. A point of clarification about
vision though, because cerebral control is contralateral the left visual field
is seen on the right occipital lobe and vice-versa. Further, since one-half of
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each visual field is seen on each retina, the halves of the visual fields must
unite at some point along the way to the visual cortex. This occurs at a
structure called the optic chiasma, where fibers of the inside halves of the
right and left optic nerves cross to the opposite side (illustrated in Figure
16.14). After the fibers have crossed and the left and right visual fields are
completed, the name of the fibers changes to optic tract (from the previous
optic nerve). Following a synapse on the thalamus (remember that all
information accessing the cerebrum must synapse on the thalamus), visual
information is projected to the visual areas on the occipital lobe by way of
optic radiations, completing the pathway for vision.
The sensory receptors for hearing and balance are situated close to
one another in the inner ear. Therefore, it is not unusual for a person who
has a hearing deficit involving the inner ear to also manifest a balance
problem. This is particularly common among older adults and may add to
the risk of sustaining a serious injury from a fall.
The outer ear (see Figure 16.16) consists of a long canal, the
external auditory meatus that ends internally at the tympanic membrane.
Its role is to transmit auditory sensations, which are vibrations in the air.
These vibratory pulsations cause the tympanic membrane to more back
and forth.
Anchored to the tympanic membrane are three small bones, the
auditory ossicles (see Figure 16.16). Between the ossicles are joints that
move in response to movements of the tympanic membrane. One of the
auditory ossicles (the stapes) rests against the oval window of the inner
ear. A pharyngotympanic (auditory) tube connects the throat (pharynx) to
the middle ear. As an aside, the infections that affect many children as
otitis media (an "ear infection") find origin in the pharynx and travel up
the tube to spread the infection to the middle ear.
The inner ear consists of sensory receptors for hearing and balance.
Those for balance are the utricle, saccule and semicircular ducts (see
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Figures 16.18 and 16.21).The utricle is the receptor for linear movement of
the head (as in flexing and extending/nodding the head "yes"). The saccule
allows us to maintain orientation against gravity—static equilibrium. The
semicircular ducts monitor rotational/angular acceleration of the head (as
in rotating the head, or shaking the head "no"). All of the receptors
function in about the same way (see Figures 16.21, 16.22), where a material
(e.g., otolithic membrane, cupula) lags behind a movement of the head.
Eventually the material moves but with some latency compared to the
movement of the head. Once the material moves, it stimulates receptor
hair cells, and then the fibers of the vestibular part of the eighth cranial
nerve.
The neural pathway for balance does not travel to the cerebrum for
the most part, as with most other sensory modalities. Instead, balance
information travels to vestibular nuclei in the medulla oblongata and the
cerebellum.
Detail of the auditory portion of the inner ear is illustrated in Figure
16.23. But perhaps a better way to understand the cochlea is displayed in
the Figures 16.16, 16.19 and 16.23. The stapes causes vibrations against the
oval window, which in turn causes vibrations in the fluid (perilymph) of
the scali vestibule. The vibrations are further conveyed from the scali
vestibule to the fluid (endolymph) of the cochlear duct. These vibrations
cause the basilar membrane inside the cochlear duct to vibrate,
stimulating receptor hair cells for hearing (for a closer view see Figure
16.19). Once the hair cells bend the cochlear portion of the eighth cranial
nerve is stimulated.
Unlike, balance information, auditory information is conveyed to
the cerebral cortex (primary auditory area on the temporal lobe) after a
synapse on the thalamus. Compared to vision, where all impulses from the
retina on one side travel to the opposite cerebral hemisphere, auditory
information from each ear travels to each hemisphere. This is why a
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person can still hear in both ears even though trauma (e.g., a stroke) may
destroy the primary auditory cortex on one cerebral hemisphere. However,
as mentioned in the lesson on the CNS, damage to language areas on the
dominant hemisphere will result in difficulty using language (aphasia)
even though the person can hear.
Sample Questions
Try these after you believe you have mastered the material covered
in the objectives.
1. Where are sensory receptors for smell located? a. vomer b. nasal mucosa c. palate d. pharynx
2. Which cranial nerve does not carry sensory information for taste?
a. facial b. glossopharyngeal c. trigeminal d. vagus
3. This part of the fibrous tanic of the eye is white, tough, and opaque. a. cornea b. choroid c. sclera d. retina
4. This part of the ears contains the auditory ossicles. a. external b. middle c. internal
5. The stapes transmits vibrations against the oval window of the inner ear, causing this to move. a. utricle b. perilymph c. saccule d. tectarial membrane
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Answers to Sample Questions
1. b; 2. c; 3. c; 4. b; 5. b
Go on to Lesson 17.
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Lesson 17 Endocrine System
Reading Assignment
Read Chapter 25 in your textbook. As always, use the objectives to
key your reading.
Objectives
By the end of this lesson, you should be able to:
1. Define and differentiate exocrine and endocrine glands.
2. Identify and locate the major endocrine glands (see Figure 25.1).
3. Define the three basic types of hormones: steroids, proteins, and
amines.
4. Describe control of hormone secretion by negative feedback
mechanisms and neural control pathways. Also, define the three
mechanisms for control of hormone release (humoral, neural,
hormonal—see Figure 25.2).
5. Generally describe how nervous and endocrine systems interact at
the pituitary gland (hypophysis) and hypothalamus.
6. List the hormones of each of the following endocrine glands and
their general effects: pituitary (hypophysis), thyroid, parathyroids,
adrenals, pancreas, ovaries, testes, and thymus.
7. Describe the etiology of diabetes mellitus (Type I and Type II) and
contrast it with diabetes insipidus.
Discussion
Hormones are blood-borne molecules that travel to certain cells
and cause a physiologic response. Endocrine glands do their work by
secreting hormones that travel in the bloodstream and influence other
cells to perform certain physiological tasks, increase or decrease the speed
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of a certain process or cause other endocrine glands to secrete yet other
hormones. Hormones eventually find their way into the blood stream
where they can move more quickly to their target cells—the cells that
respond to the hormone. The aim of the endocrine system and its
hormones is to maintain homeostasis, all things functioning normally and
in a well-adjusted fashion in the body's internal environment.
Endocrine glands contrast with a second type of gland in several
ways. Exocrine glands never secrete hormones, their products tend to be
substances such as oil, sweat, enzymes, etc. Exocrine gland products are
secreted onto epithelium, tubes, body cavities, or covering and lining
epithelium. For example, sweat is secreted onto the skin, covering
epithelium. Because of this, secretions from one exocrine gland do not
have a widespread effect relative to the hormones of an endocrine gland.
Hormones are distributed widely via the vascular system.
Endocrine glands tend to operate by way of a negative feedback
loop. This means they operate just like the thermostat in your house. If the
temperature falls, the thermostat detects it and turns on the furnace.
When the temperature increases to an acceptable level, the thermostat
causes the furnace to turn off. Decreases in temperature bring about (the
opposite) an increase in the activity of the furnace (and vice versa).
Likewise, presence or absence of certain products or substances in
the blood stream are detected by the endocrine gland, causing hormone
secretion to turn on or off, according to need. In this way, the internal
environment of the body is kept in proper working order—in balance, in
homeostasis. This sort of feedback control is characteristic of humoral
control of hormone release (see Figure 25.2). Besides humoral control,
endocrine glands may be controlled by other (tropic) hormones secreted
by the pituitary gland, or by direct nervous stimulation called hormonal
and neural control respectively (see Figure 25.2).
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Identify the major endocrine glands in Figure 25.1. You should be
able to locate all of the glands and give an anatomical description of where
each is found.
Hormones are of three basic types: steroids, proteins, or amines.
The hormones differ in how each brings about changes in target cells.
Steroid hormones can enter target cells and alter protein synthesis within
the cell.
Protein and amine hormones bind with receptor sites on the target
cell membrane causing changes in the cell membrane, which in turn may
cause changes in a variety of inter-cellular activities.
Perhaps the single most important endocrine gland is the pituitary
(also called the hypophysis, sometimes called the "master" endocrine
gland). It is located in the sella turcica of the sphenoid bone. The pituitary
can actually be thought of as two glands in one, the anterior (also called
the adenohypophysis) and posterior (also called the neurohypophysis)
pituitary glands. The pituitary and hypothalamus represent the meeting of
the nervous system and the endocrine system. This is more than just a
meeting, however, because the hypothalamus can have a great influence
on the pituitary gland. The hypothalamus and the pituitary are portrayed
in Figures 25.3 through 25.5.
The hypothalamus exerts much of its control over the anterior
pituitary (adenohypophysis) through the use of releasing factors.
Releasing factors pass from the hypothalamus to the anterior part of the
pituitary via blood vessels in the infundibulum and cause the anterior
pituitary to secrete its hormones (see Figure 25.4). Some of the pituitary
hormones then act on target cells that are non-specific. That is, growth
hormone stimulates many different cells to grow: bone, muscle, or fat
tissue. In contrast, the anterior pituitary also secretes a series of hormones
that act on still other endocrine glands. The target cells for these hormones
are other glands. The second group of hormones are referred to as tropic
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hormones. For example, thyroid stimulating hormone is a tropic hormone
because it stimulates the thyroid gland. Table 25.1 lists the primary actions
of the hormones of the pituitary. See Figure 25.4 for the relationship
between the anterior pituitary and the hypothalamus.
Turning to the posterior pituitary, (neurohypophysis) we find that it
secretes only two "hormones," oxytocin and antidiuretic hormone (ADH).
Closer inspection of the posterior pituitary (see Figure 25.5) reveals that
axons from the hypothalamus extend through the infundibulum into the
posterior pituitary. As a result, oxytocin and antidiuretic hormone are
actually closer to neurotransmitter substances, manufactured in the
hypothalamus, transported to the posterior pituitary and then secreted
into the bloodstream by the posterior pituitary. The supraoptic nucleus
produces ADH in the hypothalamus, while the paraventricular nucleus
produces oxytocin in the hypothalamus. Both are then secreted by the
neuro-hypophysis.
Study Table 25.1 and remember the major action of each of the
pituitary's hormones. To make your task a little easier, the tropic
hormones usually tell you a lot about where their target cells are. Use this
information to deduce each tropic hormone's effect. Also, for lutenizing
hormone and follicle stimulating hormone, just remember that they are
both involved in development of mature gametes (sperm cells or egg cells),
preparation for fertilization and gestation, and production of sex
hormones (estrogen and testosterone).
The thyroid gland is situated in the neck, anterior to the trachea,
superior to the sternum, and inferior to the larynx (see Figure 25.6). The
thyroid plays a major role in augmenting metabolic activity by controlling
the rate of metabolism. This is accomplished through the secretion of
thyroid hormones. A second hormone secreted by the thyroid is calcitonin.
Along with parathyroid hormone (discussed below), calcitonin regulates
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blood calcium levels. The presence of an adequate level of calcium in the
bloodstream is essential for life.
The parathyroid glands (there are usually four of them) are located
on the posterior surface of the thyroid (see Figure 25.7). Parathyroid
hormone is the only hormone produced and secreted by the parathyroid
gland. You should know how it acts to increase blood calcium: releasing it
from bone, stimulating its absorption in the digestive tract, and retaining
it through the kidneys. (Just for fun: can you remember the tissue we
discussed earlier that serves as a storage area for calcium?)
The adrenal glands sit atop the kidneys (see Figure 25.8); this is
why they are sometimes called the suprarenal glands. The adrenal gland is
a fairly complex structure, with three different zones or levels to its outer
shell (cortex), and a centrally located medulla (center). Each of these four
constituents gives rise to its own hormone. Read about each of these
hormones and their general effects in the textbook. With regard to the
adrenal medulla, some further comment is necessary. If you pay special
attention to the section on the adrenal medulla, you will find that
splanchnic nerves (preganglionic axons) from the sympathetic division of
the ANS innervate the adrenal medulla. Second, you will find that the
hormones secreted by the adrenal medulla produce the same effects as the
sympathetic division of the ANS. It is no coincidence that norepinephrine
is the transmitter substance for postganglionic axons of the sympathetic
division of the ANS and also a hormone secreted by the adrenal medulla.
In a sense you might think of the adrenal medulla as yet another ganglion
that preganglionic fibers from the sympathetic division of the ANS can
synapse on.
The pancreas is involved in the regulation of blood glucose (sugar).
It is pictured in Figures 25.1 and 25.10. It is located posterior to the
stomach and first part of the small intestine, the duodenum. The pancreas
is part exocrine gland, concerned with the secretion of digestive enzymes.
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But its endocrine functions command our attention for the purposes of the
present lesson. It secretes two hormones that produce opposite effects.
Insulin decreases blood glucose, while glucagon increases blood glucose.
Insufficient or absent secretion of insulin results in diabetes mellitus, with
the familiar excess of glucose in the bloodstream and urine.
The ovaries (female) and testes (male) together are referred to as
the gonads. You can locate each of the gonads on the composite Figure
25.1. The gonads secrete what are generally known as sex hormones
(testosterone in the male; estrogen and progesterone in the female). In
general, sex hormones control secondary sex characteristics (placement of
hair, relative amounts of muscle and fat, weight of skeleton, etc.),
stimulate maturation of gametes (egg cells and sperm cells), and promote
activities that support pregnancy.
The thymus gland (see Figure 25.1) is located posterior to the
sternum in the upper center portion of the chest. The thymus gland is not
well understood, but it has been implicated in the body's immune system.
Its major role seems to be production of a specialized white blood cell
known as a T-lymphocyte. Because of its role in the immune system, the
thymus gland and T-lymphocytes are among the most studied tissues in
AIDS research.
Sample Questions
1. This name is given to a hormone that acts on another endocrine gland. a. feedback hormone b. acceleratory hormone c. tropic hormone d. inhibiting hormone
2. Which endocrine gland listed below is most closely related to the
sympathetic division of the ANS? a. pancreas b. adrenal medulla c. parathyroid
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d. thyroid
3. Why is the posterior pituitary not a typical endocrine gland? a. It receives a rich blood supply. b. It does not make its own hormones. c. It is not near the brain. d. It contains ducts.
4. Name the antagonistic hormones that regulate blood calcium.
a. insulin-glucagon b. aldosterone-cortisone c. PTH-calcitonin d. HGH-ADH
5. Hypophysis is another name for this gland.
a. pituitary b. testes c. pancreas d. thyroid
Answers to Sample Questions
1. c; 2. b; 3. b; 4. c; 5. a
Examination #3
Examination #3 follows Lesson 17. This will be a one-hour,
supervised examination. No books, notes, or other aids may be brought to
the exam. The examination consists of forty multiple-choice questions of
the same type you have seen in the sections of sample questions in each
lesson. The exam questions are allocated according to the number of
objectives per topic.
Please read the information regarding exam scheduling and policies
posted on the ICON course Web site carefully. Students with access to the
Internet must use the ICON course Web site to submit exam requests
online. Students who do not have access to the internet may submit the
Examination Request Form located at the back of this Study Guide (print
version only).
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UNIT 5 VISCERAL SYSTEMS
Lesson 18 Heart
Lesson 19 Blood Vessels and Lymphatics
Written Assignment #7
Lesson 20 Respiratory System
Lesson 21 Digestive System
Written Assignment #8
Lesson 22 Urinary System
Lesson 23 Reproductive System
Examination #4
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Lesson 18 Heart
Reading Assignment
Read Chapter 18 in your textbook pertaining to the heart. You
might be surprised by the relatively few objectives for this important
organ. However, to answer each objective, you will have to know quite a bit
of information.
Objectives
By the end of this lesson, you should be able to:
1. Define the functions of the circulatory system. Also define atrium,
ventricle, systole, diastole, pulmonary circuit, and systemic circuit.
2. Describe the location of the heart in the mediastinum (see Figure
18.2).
3. Identify the structure of the pericardium and heart wall (Figure
18.3).
4. Identify the sulci, chambers, great vessels and valves (and papillary
muscles) of the heart on both anterior, posterior, and internal views
(Figure 18.5).
5. Trace the course of a erythrocyte through the heart and lungs,
beginning at the right atrium and ending at the aorta. Define
structural and functional differences between the left and right
heart.
6. Identify the origin of the heart beat and the intrinsic conduction
system of the heart (Figure 18.14). Identify the effects of
sympathetic and parasympathetic stimulation of the heart (Figure
18.15).
7. Identify the major vessels of coronary circulation (Figure 18.16) and
the general areas each supplies or drains.
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8. Identify major risk factor for cardio-vascular disease. Define a
Hence, the cerebral cortex is also involved in neurological control of
respiration.
Chemoreceptors in the carotid and aortic bodies send sensory
information to respiratory centers in the brainstem via the
glossopharyngial and vagus nerves (see Figures 21.17 and 21.18). This
allows for moment-to-moment correction of ventilation and respiration.
On your own, look up the clinical applications in objective number
8. You should be able to define each term.
Sample Questions
1. This name is given to the exchange of gases between the lungs and blood. a. inspiration b. expiration c. internal respiration d. external respiration
2. What is the total number of lobes in both lungs?
a. 6 b. 5 c. 4 d. 2
3. Which of the following is not a part of the respiratory system?
a. nose b. eustachian/auditory tube c. pharynx d. larynx
4. Which of the following would not be found in an alveolus of the lung?
a. macrophages b. simple epithelium c. Type II aveolar cells d. plasma cells
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5. Which of the following areas of the brain helps control respiration? a. cerebellum b. hypothalamus c. midbrain d. pons
Answers to Sample Questions
1. d; 2. b; 3. b; 4. d; 5. d
Go on to Lesson 21.
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Lesson 21 Digestive System
Reading Assignment
Read Chapter 22 in your textbook.
Objectives
1. Name the primary functions of the digestive system. Identify the
major organs and tubes associated with digestion (Figure 22.1).
2. Identify and define the peritoneum, mesentery, mesocolon,
falciform ligament, lesser omentum, and greater omentum (Figure
22.10).
3. Describe the general histology (Figure 22.5) of the GI tract: mucosa,
submucosa, muscularis, and serosa.
4. Identify the structures of the upper part of the digestive system
(Figure 22.12): oral cavity, tongue, palate, oropharynxs, and
esophagus. Also name and identify the three major salivary glands
(Figure 22.16).
5. Describe internal and external anatomy of the stomach and its
major functions (Figure 22.18).
6. Identify the different parts of the small (Figures 22.1 and 22.21) and
large intestines (Figures 22.1 and 22.22). State the primary
functions of the small and large intestines.
7. Identify and locate the organs of the digestive system and accessory
organs of digestion: liver, gallbladder, pancreas (Figures 22.26,
22.20). Generally describe the digestive functions of the liver,
gallbladder, and pancreas.
Discussion
The obvious functions of the digestive system all relate to activities
designed to facilitate the absorption of nutrients, water, and trace minerals
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through the lining of the digestive tract, especially the small and large
intestines. Digestion actually refers to the mechanical and chemical
breakdown of food, which is a pre-requisite to absorption.
The major organs of the digestive system are illustrated in Figure
22.1. I will be summarizing the major anatomical and functional features
of each of the organs and tubes in Figure 22.1 throughout this lesson.
We have already observed that the heart and lungs are enveloped in
protective layers of epithelial and connective tissue. The same holds for
some of the components of the digestive system. The general term used to
refer to these protective and stabilizing membranes is peritoneum. The
parietal peritoneum lines the inner surfaces of the abdominal cavity and
the visceral peritoneum actually touches the organ/structure (Figure
22.9).
The peritoneum can be further divided into sub-units depending on
placement and organ it is associated with. As the parietal peritoneum
extends anteriorly from the dorsal wall of the abdomen, it forms a double-
layered membrane which envelopes most of the organs of the abdominal
cavity. Depending on the organ, the double-layered membrane of
peritoneum may suspend the organ from the posterior wall of the
abdomino-pelvic cavity (see Figure 22.9). If it suspends the small
intestine, then it is called the mesentery. If it suspends a part of the large
intestine, then it is called the mesocolon (Figure 22.10). In sum, the
mesentery and the mesocolon serve to suspend the intestines from the
posterior abdominal wall, leaving the intestines enough latitude for
movement, but keeping them stabilized through attachment to the
posterior abdominal wall.
Several other parts of the double-layered part of the peritoneum are
also illustrated in Figure 22.10. These structures include: the falciform
ligament, which supports the liver anteriorly, the lesser omentum, which
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suspends the stomach from the liver, and the greater omentum, which
loosely attaches the lower portion of the stomach to the transverse colon.
The peritoneal covering continues around the organs of the
digestive system, where it is known as the visceral peritoneum (Figure
22.9). This is in keeping with the convention we have observed for the
heart and the lungs already (e.g., the visceral pleura covers the lungs).
A typical cross-section through the digestive tract reveals that it is a
multi-layered organ with specialized tissues at each layer (Figure 22.5).
The innermost layer is called the mucosa. It is composed of epithelium, as
you probably guessed. It is the portion of the digestive tract responsible for
absorptive functions. The mucosa also contains a thin layer of smooth
muscle called the muscularis mucosa. (Do not confuse this with the
muscularis layer described below. This thin layer of smooth muscle is
actually included in the mucosa layer.)
The second layer is called the submucosa (see Figure 22.5); it is
composed of loose connective tissue which is highly vascular. The
submucosa is very important to the process of absorption of nutrients, as it
contains many blood vessels and lymphatic channels which pass close to
the surface of the lumen of the digestive tract.
The third layer of the digestive tract is the muscularis layer (see
Figure 22.5). It is specialized to churn and mix food. It may also contract
in a manner that will move food further down the digestive tract
(segmentation, peristalsis).
The fourth layer of the typical segment of the digestive tract is
known as the serosa (see Figure 22.5). It is a membrane of epithelial cells
covering loose connective tissue.
In the superior reaches of the digestive system one can observe
several structures in common with the respiratory system (Figure 22.12).
The two systems share a common passageway for a brief period, the
portion of the pharynx posterior to the oral cavity. The mouth, tongue, and
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the palate are included in the digestive system but not the respiratory
because air enters through the nasal cavity, superior to the palate. The
respiratory and digestive systems diverge from one another at the inferior
portion of the pharynx, where the larynx is positioned anteriorly and the
esophagus is positioned posteriorly. As previously mentioned in the
respiratory lesson, the epiglottis covers over the glottis (the opening to the
larynx) so that food may pass over the air passage instead of being inspired
into the trachea or lungs.
You should study Figure 22.16 next. Identify the three major
salivary glands and the general location of each. The salivary glands
secrete digestive enzymes to initiate the process of breaking down the
food.
After food passes down the esophagus it enters the stomach (Figure
22.18). It is here that the digestive process continues in earnest, although
little in the way of absorption occurs in the stomach. Instead, the stomach
secretes a number of digestive enzymes, (e.g., pepsin) that transform the
food into a state more suitable to absorption. By the time the food has
been processed by the stomach it is called chyme. Make certain to identify
by landmarks on the internal and external stomach
The stomach is a J-shaped organ. The concave portion is called the
lesser curvature and the convex inferior part of the "J" is the greater
curvature. These represent the attachments of lesser and greater omentum
respectively. The most superior part of the stomach is called the fundus,
while the superior part in the area of the esophagus is called the cardia.
The area of the stomach near the first part of the small intestines is known
as the pylorus. Note, the folded inner surface of the stomach known as the
rugae.
The majority of nutrient and water absorption is the job of the small
and large intestines. The small intestine absorbs most of the food, and the
large intestine absorbs most of the water and minerals.
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The small intestine is composed of the three parts (Figure 22.1). In
order from the stomach to the large intestine, one would encounter the
duodenum (the first ten inches), the jejunum (the next three feet), and the
ileum (the remaining six-seven feet). The ileum ends at the ileocecal valve
which leads into the cecum of the large intestine. Together, the three parts
of the small intestine receive digestive secretions from the liver, pancreas,
and gall bladder, continue the breakdown of the chyme, and absorb
nutrients.
The large intestine or colon (Figure 22.22) consists of several parts
as well. The large intestine begins as the cecum, a pouch at the inferior
extent of the ascending colon. This is a short segment of the large
intestine; the appendix is a blind pouch that is suspended form the cecum.
Absorption of nutrients ends in the small intestines, but the large
intestines still has the important job of absorbing water and minerals.
Extending in a superior direction from the cecum is the ascending
colon. It turns medially at the hepatic flexure and becomes the transverse
colon. The transverse colon runs across the anterior body wall and then
turns inferiorly at the splenic flexure to become the descending colon.
From this point the colon ends in three short segments: a short sigmoid
colon, the rectum, and the anal canal (Figure 22.22).
Other features to note on Figure 22.22 include the haustra,
dilations in the large intestine throughout its course. The haustra are
periodic dilations where the contents of the large intestine pause for
further mixing and absorption of water and minerals. The large intestine is
also covered with a longitudinal muscle throughout its entire length called
the taeniae coli. The taeniae coli are capable of strong peristaltic
contractions that move the contents of the large intestine along toward the
rectum for defecation.
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Assisting in the digestion and absorption of food are three accessory
organs: the liver, gall bladder, and pancreas. All three secrete enzymes that
assist in digestion.
The liver is situated in the superior right portion of the abdominal
cavity (Figures 22.21, 22.26), just inferior to the diaphragm. The liver has
four lobes; left, right, caudate, and quadrate. The latter two are seen only
on an inferior view. The liver is attached to the anterior body wall by the
falciform ligament.
From our earlier discussion of hepatic portal circulation you know
that the liver plays an important role in the filtration of blood from the
intestines. Indeed, important functions of the liver include the removal of
old erythrocytes, filtration of bacteria and toxins, and storage of glucose in
the form of glycogen.
From the point of view of digestion, however, the essential function
of the liver is production of bile. Bile is needed in the breakdown and
absorption of fats in the digestive tract. The liver produces bile that is
stored in the gall bladder (Figure 22.26). When bile is to be secreted into
the duodenum, the gall bladder secretes bile into the cystic duct and the
liver secretes bile into the common hepatic duct. These two structures join
to form the common bile duct to the duodenum (Figure 22.20).
The last of the accessory digestive organs is the pancreas (see
Figure 22.20). You may recall that the pancreas is an endocrine gland. In
fact, it has both endocrine and exocrine functions. The latter are
associated with the digestive system. Like the liver and the gall bladder,
the pancreas has a duct that leads to the first part of the small intestine
(Figure 22.20). The pancreas secretes pancreatic juice into the pancreatic
duct. The pancreatic duct joins with the common bile duct at the
duodenum to form the hepatopancreatic ampulla (Figure 22.20). The
pancreatic juice contains enzymes that assist in the digestion of
carbohydrates, fats, and proteins.
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Sample Questions
1. Name the portion of the peritoneum that suspends parts of the large intestines from the posterior wall of the abdominal cavity. a. mesocolon b. mesentery c. lesser omentum d. retroperitoneum
2. This part of the small intestine would be cut first if surgery was being
performed to remove an obstruction from the duodenum. a. mucosa b. muscularis c. serosa d. submucosa
3. This part of the digestive system is shared with the respiratory system.
a. larynx b. pharynx c. palate d. submandibular gland
4. This structure is the first that would be encountered by a button
swallowed by a child after the button passed through the ileum. a. cecum b. hepatic flexure c. ascending colon d. jejunum
5. The lesser omentum connects the liver to which of the structures listed
below? a. stomach b. pancreas c. spleen d. gall bladder
Answers to Sample Questions
1. a; 2. c; 3. b; 4. a; 5. a
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Written Assignment #8
Instructions
Instructions for submitting assignments electronically in the ICON
Drop Box are posted on the ICON course site under "Submit
Assignments."
Description
This assignment is worth 10 points.
1. Trace a button swallowed by a child through the digestive system,
noting anatomical structures it would pass through from oral cavity
to anus.
2. Three major accessory digestive organs contribute digestive
enzymes to the process by way of the hepatopancreatic ampulla.
Identify the three organs and their enzymes. Also explain how
enzymes from each organ reach the hepatopancreatic ampulla.
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Lesson 22 Urinary System
Reading Assignment
Read Chapter 23 on the urinary system. Pay attention to the
objectives for the lesson.
Objectives
1. Identify the organs of the urinary system (Figure 23.1). Also, state
the functions of the urinary system.
2. Describe the external (location, hilus) and internal anatomy of the
kidneys: cortex, medulla, renal pyramids, minor calyx, major calyx,
and renal pelvis (Figure 23.3).
3. Define the microscopic anatomy of a nephron: glomerulus,
glomerular capsule, tubules, loop of Henle, vasa reta, peritubular
capillaries, collecting tubule, and papillary duct (Figures 23.4 and
23.5).
4. Describe the basic functions of each part of a nephron: filtration,
reabsorption, secretion.
5. Name the tissue layers of the ureters and the urinary bladder, (also
identify detrusor muscle, rugae).
6. Identify the urethra (and sphinctors) and the bladder trigone
(Figure 23.16).
7. Describe the normal micturation and identify the nervous control of
micturation: visceral afferent neurons, micturation center (pons),
parasympathetic, sympathetic, and somatic pathways (see Figure
23.17).
8. Trace a voided molecule of water from kidney to urethra.
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Discussion
Like the digestive and respiratory systems earlier, the urinary
system is a network of tubes connecting various organs. It also transports
fluid like the vascular system. But as you can see by Figure 23.1 the urinary
system is a lot more simple and quite a bit shorter than the digestive
system.
The kidneys drain into two tubes on either side of the abdominal
cavity. These tubes are called ureters. The ureters drain into the urinary
bladder, which in turn drains urine into the urethra to be voided from the
body. The components of the urinary system are identified in Figure 23.1.
The primary functions of the urinary system are to filter blood for
toxins and waste products, and to secrete excess water. The kidneys help
maintain the balance of electrolytes and the amount of water in the body
at suitable levels.
The kidneys are located against the posterior abdominal wall
between T12 and L3 vertebrae and the beginning of the lumbar vertebrae.
They are also retroperitoneal (posterior to the peritoneal membranes).
Normally, people have two kidneys, but it is not unusual to have only one
kidney.
Though larger, the kidneys are shaped similar to the lymph nodes,
somewhat like a lima bean. The concave surface has a hilus, like the lymph
node. Similarities end there, however, because the kidneys are responsible
for filtering blood not lymph.
Figure 23.3 reveals the gross appearance of the kidney. It has a
peripherally located cortex surrounding an inner medullary area. Tubes
are plentiful throughout. The minor calyces then unite to form the major
calyx. Major calyces converge at the renal pelvis and hilus of each kidney.
Ureters begin at the hilus of each kidney.
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The histology of the kidney is represented by the basic functional
unit called the nephron. A nephron is illustrated in Figures 23.4, 23.5, and
23.9. A network of capillaries, the glomerulus (Figure 23.6), filters blood
and permits the filtrate of water and waste products to enter the proximal
part of the nephron. Most of the water is reabsorbed from the nephron's
tubules back into the vascular system through capillaries surrounding the
tubules of the nephron (Figure 23.9).
The tubule leading from the nephron does not lead directly to the
collecting duct of the nephron, but rather the tubule is tortuous (winding)
and include a lengthy, convoluted section proximally, a nephron loop, and
a lengthy, distal convoluted tubule (Figure 23.5). From the collecting duct
of each individual nephron, the urine passes into the medulla of the kidney
where it is received by the minor calyx (when it can be properly called
urine) and then on to the major calyx and into the ureter.
The nephron works through three processes—filtration,
reabsorption, and secretion. Filtration occurs at the glomerulus, while
reabsorption and secretion occur in the tubules.
The ureter and the bladder are similar to the other tube systems
inside the body in the sense that each is comprised of several layers of
tissue. The general theme of the tubes within the body has been epithelium
on the inside, smooth muscle in the middle, and connective tissue on the
outside.
The ureter has an inner layer of mucosa which is comprised of
transitional epithelium. Transitional epithelium allows for considerable
distension. A middle smooth muscle layer called muscularis is likewise
found lining the ureters. Finally, an outer layer of fibrous connective
tissue, called the adventitia, completes the walls of the ureters.
The urinary bladder (see Figure 23.16) is similarly organized, with a
layer of transitional epithelium lining the inside of the bladder to permit
distention with the accumulation of urine. The second layer of the bladder
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is the smooth muscle layer, again called the muscularis (also known as the
bladder detrusor muscle). Finally, the most superficial layer of the bladder
is a continuation of the peritoneum called the adventitia.
The inferior opening in the bladder is called the urethra. It is in
close proximity to the openings of each ureter into the bladder and forms a
triangle (Figure 23.16). This area is known as the bladder trigone. Once the
urine has entered the urethra, it must pass internal and extrenal
sphincters to be expelled.
Micturation (urination) is a complex activity (see Figure 23.17) that
is part involuntary and part voluntary. Sympathetic innervation of the
smooth muscle (detrusor muscle) of the urinary bladder allows for filling.
As the bladder fills with urine, stretch receptors in the detrusor muscle of
the bladder are stimulated. This information is feedback to the spinal cord
and then upward to micturation center in the pons. The micturation center
in the pons then causes parasympathetic fibers to stimulate contraction of
the detursor muscle and relaxation of the internal sphinctor. The
micturation center inhibits somatic motor neurons innervating the
external sphinctor. Finally, sympathetic innervation of the bladder is
inhibited to allow for contraction. The cerebrum may also delay urination
for a time by somatic motor stimulation of the external sphinctor.
I will leave you to your own devices to satisfy the final objective of
tracing a water molecule from the kidney to the urethra. Make certain to
detail the pathway followed by the water as it negotiates the complexities
of the nephron. Refer to Figures 23.1, 23.3, 23.5, 23.14 and 23.16 to
develop a complete answer.
Sample Questions
1. Blood is filtered by this structure in the nephron. a. proximal convoluted tubule b. loop of Henle c. glomerulus
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d. collecting duct
2. Name the tube that leads from the kidney to the bladder. a. ureter b. collecting duct c. convoluted tubule d. minor calyx
3. Which of the following is not a component of the urinary system?
a. bladder b. prostate gland c. urethra d. ureter
4. Urine passing through the ureter is in direct contact with which tunic
layer? a. muscularis b. mucosa c. submucosa d. serosa
5. As a water molecule leaves the collecting duct of the nephron, it next
enters this structure. a. ureter b. urethra c. bladder d. minor calyx
Answers to Sample Questions
1. c; 2. a; 3. b; 4. b; 5. d
Go on to Lesson 23.
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Lesson 23 Reproductive System
Reading Assignment
Read Chapter 24 in the textbook. Use the objectives below to guide
your reading.
Objectives
1. List the functions of the reproductive system.
2. Identify and describe structures of the male reproductive system