Chapter 10

Copyright © John Wiley and Sons, Inc. All rights reserved.

Chapter 10

Muscular

Tissue

Lecture slides prepared by Curtis DeFriez, Weber State University


Like nervous tissue, muscles are excitable or

"irritable”

they have the ability to respond to a stimulus

Unlike nerves, however, muscles are also:

Contractible (they can shorten

in length)

Extensible (they can extend or

stretch)

Elastic (they can return to their

original shape)

Functions of Muscular Tissue


Muscle makes up a large percentage of the body’s

weight

Their main functions are to:

Create motion – muscles work with nerves, bones,

and joints to produce body movements

Stabilize body positions and maintain posture

Store substances within the body using sphincters

Move substances by peristaltic contractions

Generate heat through thermogenesis

Functions of Muscular Tissue


Three Types of Muscular Tissue


(b) Cardiac muscle (c) Visceral smooth muscle

(a) Skeletal muscle

Three Types of Muscular Tissue


Skeletal Muscle


Skeletal Muscle


Skeletal muscle fibers are very long “cells” -

next to neurons (which can be over a meter

long),

perhaps the longest in the body

The Sartorious muscle contains

single fibers that are at least

30 cm long

A single skeletal muscle fiber

Skeletal Muscle


Sarcolemma

Motor neuron

Skeletal Muscle

The terminal processes of a

motor neuron in close proximity

to the sarcolemma of a skeletal

muscle fiber


The epimysium, perimysium, and

endomysium all are continuous with

the connective tissues that form

tendons and ligaments (attach

skeletal muscle to bone) and muscle

fascia (connect muscles to other

muscles to form groups of muscles)

Organization of Muscle Tissue



Organization of a single muscle

belly

Epimysium

Perimysium


Organization of a fasciculus



Organization of a muscle fiber



A muscle, a fasciculus, and a fiber all visualized



In groups of muscles the

epimysium continues to

become thicker, forming

fascia which covers

many muscles

This graphic shows the

fascia lata enveloping

the entire group of

quadriceps and

hamstring muscles in

the thing



Organization of Muscle

TissueMany large muscle

groups are encased

in both a

superficial

and a deep fascia

Real Anatomy, John Wiley and Sons


Organization of Muscle TissueAn aponeurosis is

essentially a thick

fascia that connects

two muscle bellies.

This epicranial

aponeurosis connects

the muscle bellies of

the occipitalis and

the frontalis to form

“one” muscle: The

occipitofrontalis

Epicranial aponeurosisFrontal belly of

the occipitofrontalis m.


Veins, arteries, and nerves are located in the

deep fascia between muscles of the thigh.



Beneath the connective tissue endomysium

is found the plasma membrane (called the

sarcolemma) of an individual skeletal

muscle fiber

The cytoplasm (sarcoplasm) of skeletal

muscle fibers is chocked full of

contractile proteins

arranged in myofibrils

The Skeletal Muscle Fiber


You should learn the names of the internal

structures of the muscle fiber

Sarcolemma

Sarcoplasm

Myofibril

T-tubules

Triad (with

terminal cisterns

Sarcoplasmic reticulum

Sarcomere




Increasing the level of magnification, the

myofibrils are seen to be composed

of filaments

Thick filaments

Thing filaments


A scanning electron micrograph of a

sarcomere

The basic functional unit of skeletal muscle fibers is the sarcomere: An arrangement of thick and thin filaments sandwiched between two Z discs



The “Z line” is really a Z disc when considered in

3 dimensions. A sarcomere extends from Z disc

to Z disc.

Muscle contraction occurs in the sarcomeres



Myofibrils are built from three groups of proteins

Contractile proteins generate force during

contraction

Regulatory proteins help switch the contraction

process on and off

Structural proteins keep the thick and thin

filaments in proper alignment and link the

myofibrils to the sarcolemma and extracellular

matrix

Muscle Proteins


The thin filaments are comprised mostly of the

structural protein actin, and the thick filaments are

comprised mostly of the structural protein myosin

However, in both types of filaments, there are also

other structural and regulatory proteins

Muscle Proteins


In the thin filaments actin proteins are strung

together like a bead of pearls

In the thick filaments myosin proteins look like

golf clubs bound together

Muscle Proteins


In this first graphic, the myosin binding sites on

the actin proteins are readily visible.

The regulatory proteins troponin and

tropomyosin have been added to the bottom

graphic: The myosin binding sites have been

covered

Muscle Proteins


In this graphic the troponin-tropomyosin

complex has slid down into the “gutters” of the

actin molecule unblocking the myosin binding

site

The troponin-tropomyosin complex can slide

back and forth depending on the presence of

Ca2+

Myosin binding site exposed

Muscle Proteins


Ca2+ binds to troponin which changes the shape of

the troponin-tropomyosin complex and uncovers

the myosin binding sites on actin

Muscle Proteins


• Besides contractile and regulatory proteins,

muscle contains about a dozen structural

proteins which contribute to the alignment,

stability, elasticity, and extensibility of

myofibrils

• Titan is the third most plentiful protein in

muscle, after actin and myosin - it extends

from the Z disc and accounts for much of the

elasticity of myofibrils

• Dystrophin is discussed later as it relates to

the disease of muscular dystrophy

Muscle Proteins


With exposure of the myosin binding sites on actin (the thin filaments)—in the presence of Ca2+ and ATP—the thick and thin filaments “slide” on one another and the sarcomere is shortened

The Sliding-Filament Mechanism


The “sliding” of actin on myosin (thick filaments on thin filaments) can be broken down into a 4 step process



Step 1: ATP hydrolysis

Step 2: Attachment


Step 3: Power Stroke

Step 4: Detachment




Contraction and Movement Overview

Interactions Animation

Contraction and Movement

You must be connected to the internet to run this animation.


Limited contact between actin and myosin

Compressed thick

filaments

Length-Tension RelationshipSarcomere shortening produces tension within a muscle


Excitation-Contraction CouplingWe will come back to the term excitation-

contraction coupling in a little bit

Before we can describe the

entire process, from

thinking of moving a

muscle to actual contraction

of sarcomeres, we must

first explore the processes

that occur at the neuromuscular junction


Excitation-Contraction coupling (EC coupling) involves events at the junction between a motor neuron and a skeletal muscle fiber

Neuromuscular Junction


An enlarged view of the neuromuscular junctionThe presynaptic membrane is on the neuron while the postsynaptic membrane is the motor end plate on the muscle cell. The two membranes are separated by a space, or “cleft”



Conscious thought (to move a muscle) results in

activation of a motor neuron, and release of the

neurotransmitter acetylcholine (AcCh) at the

NM junction

The enzyme

acetylcholinesterase

breaks down AcCh

after a short period

of time



The plasma membrane on the “far side” of the NMJ

belongs to the muscle cell and is called the motor end

plate

The motor end plate is rich in chemical (ligand) - gated

sodium channels that respond to AcCh. Another way to

say this: The receptors for AcCh are on the ligand-gated

sodium channels on the motor end plate



The chemical events at the NMJ transmit the electrical events of a neuronal action potential into the electrical events of a muscle action potential



Neuromuscular JunctionInteractions Animation

Neuromuscular Junctions



The muscle AP is propagated over the surface

of the muscle cell membrane (sarcolemma) via

voltage (electrical)-gated Na+ and K+ channels

Muscle Action Potential


By placing a micropipette inside a muscle cell,

and then measuring the electrical potential

across the cell membrane, the phases of an

action potential

(AP) can be

graphed (as in this

figure)



The behavior of the Na+

and K+ channels, at various

points in the AP, are seen

in this graphic

Na+ gates open during the

depolarization phase

K+ gates open during the

repolarization phase



Generating An Action PotentialThe flow of ions through cell a membrane looks a lot

like a "piece" of electricity flowing through a wire

(but not as fast)

Generating an AP on the muscle membrane involves

the transfer of information from an electrical signal

(down the neuron), to a chemical signal (at the NMJ),

back to an electrical signal (depolarization of the

sarcolemma)

This added complexity (changing from electrical to

chemical back to electrical signals) provides

necessary control of the process


Excitation-Contraction Coupling



EC coupling involves putting it all together

The thought process going on in the brain

The AP arriving at the neuromuscular junction

The regeneration of an AP on the muscle

membrane

Release of Ca2+ from the sarcoplasmic reticulum

Sliding of thick on thin filaments in sarcomeres

Generation of muscle tension (work)




The brain

The motor neuron

Acetylcholine (ACh)

Acetylcholinesterase

enzyme

Ach receptors on the

motor endplate

Na+-K+ channels on the

sarcolemma

Na+ flow

K+ flow

Regenerate AP

The T-tubules

The SR

Ca2+ release

Troponin/

Tropomyosin

ATP

Myosin binding

Filaments slide

Muscles contract

Role Players in E-C

coupling



Contraction of SarcomereInteractions Animation

Contraction of a Sarcomere



Sources of Muscle EnergyStored ATP

3 seconds

Energy transferred from stored creatine

phosphate

12 seconds

Aerobic ATP production

Anaerobic glucose use

30-40 seconds


Sources of Muscle Energy






In a state of homeostasis, muscle use of

O2 and nutrients is balanced by the production

of manageable levels of waste products like

CO2

Heat - 70-80% of the energy used by

muscles is lost as heat - muscle activity is

important for maintaining body temperature

Lactic acid (anaerobic)

Skeletal Muscle Metabolism


Oxygen Debt, or "Excess Post-Exercise Oxygen

Consumption" (EPOC) is the amount of O2

repayment required after exercise in skeletal

muscle to:

Replenish ATP stores

Replenish creatine phosphate and

myoglobin stores

Convert lactic acid back into pyruvate

so it can be used in the Krebs cycle to replenish

ATP





Muscle Metabolism

Muscle Metabolism



Cardiac and Smooth Muscle Metabolism

In response to a single AP, cardiac muscle

contracts 10-15 times longer than skeletal

muscle, and must continue to do so, without rest,

for the life of the individual

To meet this constant demand, cardiac muscle

generally uses the rich supply of O2 delivered by

the extensive coronary circulation to generate

ATP through aerobic respiration


Cardiac and Smooth Muscle Metabolism

Like cardiac muscle, smooth muscle (in your deep

organs) is autorhythmic and is not under

voluntary control (your heart beats and your

stomach digests without you thinking about it).

Unlike cardiac (and skeletal muscle) however,

smooth muscle has a low capacity for generating

ATP and does so only through anaerobic

respiration (glycolysis)


Motor Unit is composed of a motor neuron

plus all of the muscle cells it innervates

High precision

• Fewer muscle fibers per neuron

• Laryngeal and extraocular muscles (2-20)

Low precision

• Many muscle fibers per neuron

• Thigh muscles (2,000-3,000)

The Motor Unit


Florescent dye is used to show the terminal

processes of a single neuron which terminate on a

few muscle fibers

The Motor Unit


Activities requiring extreme precision (like the subtle

and rapid movements of the eye) involve muscles

with very small motor units (1-4 muscle fibers/neuron)

The Motor Unit


All-or-none principle of muscle contraction

When an individual muscle fiber is stimulated to

depolarization, and an action potential is

propagated along its sarcolemma, it must

contract to it’s full force—it can’t partially

contract

Also, when a single motor unit is recruited to

contract, all the muscle fibers in that motor unit

must all contract at the same time

The Motor Unit


Skeletal muscle fibers are not all alike in appearance

or function. By appearance:

Red muscle fibers (the dark meat in chicken legs)

have a high myoglobin content, more mitochondria,

more energy stores, and a greater blood supply

White muscle fibers (the white meat in chicken

breasts) have less myoglobin, mitochondria, and

blood supply

Skeletal Muscle Fiber Types


Slow oxidative fibers (SO) are small, appear dark red, are

the least powerful type. They are very fatigue resistant

Used for endurance like running a marathon

Fast oxidative-glycolytic fibers (FOG) are intermediate in

size, appear dark red, and are moderately resistant to fatigue.

Used for walking

Fast glycolytic fibers (FG) are large, white, and powerful

Suited to intense anaerobic activity of short duration





Most skeletal muscles are a mixture of all three types

of skeletal muscle fibers; about half the fibers in a

typical skeletal muscle are slow oxidative (SO) fibers

Within a particular motor unit all the skeletal

muscle fibers are the same type

The different motor units in a muscle are recruited

in a specific order depending on the task being

performed (fast anaerobic activity for maximal

force, etc.)



There is a brief delay called the latent period as

the AP sweeps over the sarcolemma and Ca2+ ions

are released from the sarcoplasmic reticulum (SR)

During the next phase the fiber is actively

contracting

This is followed by relaxation as the Ca2+ ions are

re-sequestered into the SR and myosin binding

sites are covered by tropomyosin

Temporary loss of excitability is call the refractory

period – All muscle fibers in a motor unit will not

respond to a stimulus during this short time

Tension in a Muscle


A twitch is recorded when a stimulus that results in

contraction (force) of a single muscle fiber is

measured over a very brief millisecond time frame

Tension in a Muscle


Applying increased numbers of action potentials to a muscle fiber (or a fascicle, a muscle, or a muscle group) results in fusion of contractions (tetanus) and the performance of useful work

Tension in a Muscle


Two motor units, one in green, the other in purple, demonstrate the concept of progressive activation of a muscle known as recruitment

Recruitment allows a muscle to accomplish increasing gradations of contractile strength

Tension in a Muscle


Muscle TensionInteractions Animation

Control of Muscle Tension



Muscle ContractionIsotonic contractions results in movement

Concentric isotonic is a type of muscle contraction

in which the muscle shorten while generating force

Eccentric isotonic is a contraction in which muscle

tension is less than the resistance (the muscle

lengthens)

Isometric contractions results in no movement

Muscle force and resistance are equal

Supporting objects in a fixed position and posture


Muscle Contraction


Exercise-induced muscle damage

After intense exercise electron micrographs

reveal considerable muscle damage including

torn sarcolemmas and disrupted Z-discs

Blood levels of proteins normally confined

only to muscle (including myoglobin and the

enzyme creatine kinase) increase as they are

released from damaged muscle

Imbalances of Homeostasis


Spasm

A sudden involuntary contraction of a single

muscle within a large group of muscles – usually

painless

Cramp

Involuntary and often painful muscle contractions

Caused by inadequate blood flow to muscles (such

as in dehydration), overuse and injury, and

abnormal blood electrolyte levels



Disease States and Disorders

Fibrosis (myofibrosis)

Replacement of muscle fibers by excessive

amounts of connective tissues (fibrous scar

tissue)

Myosclerosis

Hardening of the muscle caused by calcification

Both myosclerosis and muscle fibrosis occur as a

result of trauma and various metabolic disorders



Aging

In part due to decreased levels of physical activity,

with aging humans undergo a slow, progressive loss

of skeletal muscle mass that is replaced largely by

fibrous connective tissue and adipose tissue

Muscle strength at 85 is about half that at age 25

Compared to the other two fiber types, the relative

number of slow oxidative fibers appears to increase


Chapter 10

Documents

copyright john wiley

muscle fascia

types of muscular tissue

muscular tissue lecture

adeep fascia real anatomy

entiregroup of quadriceps

curtis defriez

main functionsareto