Muscular System - University of Medicine, Magway · 2018. 5. 23. · Related to the function of movement is the muscular system’s second function: - is the maintenance of posture

Objectives:

The students should be able to : -

1. recall the types of muscles

2. describe the functional characteristics of muscles

3. state the antagonistic muscle parts

4. describe the muscle fatigue and muscle tone

The ability to move is an essential activity of the living human body

is made possible by

" the unique function of contractility " in muscles

What is contractility ?Contractility :

The ability or property of a substance,

especially of muscle, of shortening, or becoming reduced in size, or developing increased tension. ( Reference of this chapter )

“ Movement ”

- is the main function of the muscular system

Movement of the body ( locomotion )

Figure shows movement of

individual parts of the body

Locomotion is movement or the ability to move from one place to another.

‘the muscles that are concerned with locomotion’

‘ Some people preferred walking to other forms of locomotion such as running, swimming, jumping ’

Walking ( Locomotion )

Jumping ( Locomotion )

Related to the function of movement is the muscular system’s

second function:

- is the maintenance of posture and body position

Muscles

- often contract to hold the body still or in a particular position rather than to cause movement.

- hold up the body throughout the day without becoming tired.

Reference of this chapter

Muscles help the body stay erect

Muscles determine posture .

What is posture?

Posture is how you hold your body.“ how you hold yourself when you are moving, like when you are

walking, running, or bending over to pick up something.”

“ how you hold yourself when you are not moving, like when you are sitting, standing, or sleeping.”

Reference of this chapter

Muscles maintain the Posture

Examples of posture

3. Another function related to movement

- the movement of the internal organs

- causes the movement of substances inside the body.

The cardiac and visceral muscles are primarily responsible for transporting

substances like blood or food from one part of the body to another.

Reference of this chapter

Inaddition to playing a role in movement , muscle give

the body’s “characteristic form”.

The skeleton determines the over-all body shape, but the

muscle drape the skeleton produce the contours, perceive

as “ beautiful and graceful”.

The contour and characteristic form of human body

Contour of

human body

The skeleton of the human body

Muscles drape the skeleton produce the contours

A simplified image showing peristalsis

Muscles also perticipate the less obvious

movement of the internal organs.

Peristalsis is a radially symmetrical contraction and relaxation of

muscles that propagates in a wave down a tube, in an anterograde

direction.

In much of a digestive tract

such as the human gastrointestinal tract, smooth muscle tissue

contracts in sequence to produce a peristaltic wave, which propels a

ball of food (called a bolus while in the esophagus and upper

gastrointestinal tract and chyme in

the stomach) along the tract. Peristaltic movement comprises

relaxation of circular smooth muscles, then their contraction behind

the chewed material to keep it from moving backward, then

longitudinal contraction to push it forward.

The final function of muscle tissue is the generation of body heat.

The body’s heat

The high metabolic rate of contracting muscle - -produces

"a great deal of waste heat"

Many small muscle contractions within the body produce

" our natural body heat“

Reference of this chapter

Muscles

1. allow to move the body ( locomotion ) as well as move individual parts of the body

2. help the body stay erect and determine posture

3. also perticipate the less obvious movement of the internal organs

4. give the body’s “characteristic form”

5. drape the skeleton produce the contours,

perceive as “ beautiful and graceful”

6. produce most of the body’s heat

Muscle Types in Mammals

Muscle types in mammals

There are three types of muscle tissues.

1. Skeletal muscle

2. Cardiac muscle

3. Smooth muscle

Muscle Types in Mammals

Muscles and location

1. Skeletal muscle

- Striped or striated muscle : often called voluntary muscle

( because its movement is voluntary ) .

- are also called somatic muscle.

Organization of skeletal muscle

Skeletal muscle cell (also called muscle fiber)

(A) These huge multinucleated cells form by the fusion of many muscle cell precursors, called myoblasts. In an adult human, a muscle cell is typically 50 μm in diameter and can be up to several centimeters long. https://www.ncbi.nlm.nih.gov/books/NBK26888/figure/A3066/?report=objectonly

Microscopic structure of skeletal muscle fibers

2. Cardiac muscle

- is a special type of striped muscle in the wall of heart ;

contraction is involuntary.

The walls of the heart's chambers are composed almost entirely of muscle fibers.

Muscle fiber

Cardiac muscle cells or fibers

Cardiac muscle cells

Section of cardiac muscle fibers

Microscopic structure of cardiac muscle fibers

The heart wall

3. Smooth muscle

- surrounds the walls of internal organs

such as gut , bladder , blood vessels and the uterus ;

contruction is involuntary.

Microscopic structure of smooth muscle fibers

Smooth muscle

Arrangement of smooth muscle in the walls of hollow organ.

Cross section of intestine showing the longitudinal and circular layers smooth muscle

Cross section of the blood vessel

Cross section of the blood vessels

Functional characteristics of muscles

All muscles ( Skeletal , Smooth and Cardiac ) have three

characteristics in common .

1. Contractibility

2. Extensibility

3. Elasticity

Contractibility

“ a quality possessed by no other body tissue ”

a quality : to become smaller, narrower, shorter, etc.

The sliding of actin along myosin shortens

the sarcomere, causing muscle contraction.

When a muscle shorten or contracts

Reduces the distance between the parts of its contents

or

Reduces the space it surrounds

Functional characteristics of muscle

Contractibility , extensibility and elasticity of skeletal muscle

When a muscle shorten or contracts

- reduces the distance between the parts of

its contents

Muscles can only contract.

They cannot actively extend, or lengthen

Fig : Contractibility , extensibility

and elasticity of skeletal muscle

The contraction of skeletal muscles which connect a pair of

bone

brings the attachment points closer together

causes the bone to move

Attachment

points

of biceps

Attachment

points

triceps

Contractibility , extensibility and elasticity of cardiac muscle

The walls of the heart's

chambers are composed

almost entirely of muscle

fibers.

Cardiac muscle is also an

involuntary type of muscle.

Its rhythmic, powerful

contractions force blood

out of the heart as it

beats.

Fig : Contractibility , extensibility

and elasticity of cardiac muscle

Cardiac muscle stimulates itself to contract. The natural pacemaker of the heart is made of

cardiac muscle tissue that stimulates other cardiac muscle cells to contract.

https://media.giphy.com/media/LZYul5Rtgr76E/source.gif

Network of tubules and sacs found within muscle

fibers

-Transverse tubules extend across the sarcoplasm

at right angles to the long axis of the muscle fiber

-Formed by inward extensions of the sarcolemma

-Membrane has ion pumps that continually

transport calcium ions inward from the

sarcoplasm

-Allow electrical impulses traveling along the

sarcolemma to move deeper into the cell

The human heart is a very efficient machine that beats on average about 80 times per minute for the entire lifespan of its owner. Direct

observations of rat cardiomyocytes, the individual muscle units of the heart, with a high-resolution light microscope have revealed that the

microtubules (wavy lines pictured here in red) buckle during each contraction, and act as load bearing springs that complement the contractile

apparatus. The microtubules help return the myocyte back to its original shape after contraction.

Contraction of cardiac muscle fiber

When cardiac muscles contract

reduce the area in the chambers

pumping blood from the heart into the blood vessels

Cardiac muscle contraction reduce the chambers of heart

The area ( space )

of the chambers

Transverse section of the heart

The area ( space )

of the right and

left ventricles

Transverse section of the heart

Cardiac muscles contraction pumps the blood from the heart into the blood vessels

Contractibility , extensibility and elasticity of smooth muscle

Figure : contractibility , extensibility and elasticity of smooth muscle

Contracted and uncontracted states of smooth muscle cell

Smooth muscles

- surround blood vessels and intestine causing the

diameter of these tubes to decrease upon contraction

You cannot consciously control smooth muscle contraction, and your brain releases

hormones into your blood that control smooth muscle contraction.

In this animation, the large

intestine is shown in a state of

peristalsis, which involves the

contraction and relaxation of

smooth muscle tissue to assist

the movement of food through

the digestive tract.

Intestinal Peristalsis

A simplified image showing peristalsis

Antagonistic muscle parts

An antagonistic pair

The muscles of the body are arranged in pairs.

One produces movement in a single direction,

the other does so in the opposite direction.

This arrangement of muscles with opposite

action is known as “ an antagonistic pair ”.

The opposite direction of antagonistic pairs

The antagonistic muscle pair

One produces movement in a single direction,

the other does so in the opposite direction.

Muscles

are attached to the bones by non elastic cords called

tendons

Muscles

attach to the bone of the skeleton

or

the bone of some other structure

Most skeletal muscle is attached to bone on its ends by way of what we call tendons. As the

muscles contract, they exert force on the bones, which help to support and move our body

along with its appendages.

https://books.google.com.mm/books?id=5LsaCgAAQBAJ&pg=PA121&lpg=PA121&dq=Skeletal+muscles+are+attached+to+bone+in+such+a+way

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Most skeletal muscle is attached to bone of some other structures by tendon such as eyeball.

Bones are connected by joints.

Skeletal muscles

- are attached in such

a way as to bridge these Joints

So,

when skeletal muscle contracts

the bone to which it is attached

will move

The muscle as a whole

- is surrounded by a thin sheet of connective tissue , epimysium

Within the muscle

perimysium surrounds and separates the bundles ( fascicles )

endomysium surrounds and separates the muscle cells( fibers )

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info/pdf/marieb-0321927028-chapter9.pdf

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Section of skeletal muscle

Skeletal muscle

- consists of many bundles

of muscles

A bundle of muscle cells

- is called a fascicle

A muscle cell

- consists of many myofibrils

Each muscle fiber

- is wrapped by a layer of

loose connective tissue

called endomycium ( a

loose connective tissue ).

The endomycium

- not only lends physical

support to each muscle

fiber, but also supports the

small blood vessels and

nerve arborizations that

supply the tissue.

Examine fibers cut in long section with the low-power

objective. Individual skeletal muscke cells are called muscle

fibers.

Skeletal striated muscle fibers in cross section showing the presence of several nuclei

(multinucleated cells) located in the cell periphery. Light microscope photomicrograph

Skeletal Muscle

cross section ( CS )

long section ( LS )

Muscle fibers never attach directly to

bone or cartilage

The attachment is always mediated

by connective tissue fibers

Epimysium ( together with the perimysium

and endomysium layers of connective tissue )

generally extend beyond the fleshy part

of muscle, forming a thick rope-like tendon .

a thick rope-like

tendon

Origin and insertion

The origin

- is the part of a skeletal muscle

- is attached to a fixed structure or bone

- moves least during muscle contraction

The insertion

- is the other end of skeletal muscle

- is attached to a movable part ( bone )

- moves most during muscle contraction

Attachment

points

of biceps

Attachment

points

of triceps

Origin and Insertion of Biceps .

A skeletal muscle attaches to bone (or

sometimes other muscles or tissues) at

two or more places. If the place is a

bone that remains immobile for an

action, the attachment is called an origin.

If the place is on the bone that moves

during the action, the attachment is

called an insertion.

The triceps brachii have four

points of attachment :

- one insertion on the ulna

- three origins

two on the humerus

and

one on the scapula

Muscles always work in pairs

- The agonist is the primarily

responsible for producing a

movement

- The antagonist is the muscle

which relaxes while the

movement

An antagonistic pair

They never completely

relax – always a few

contracted fibres in

every muscle making

them slightly tense =

muscle tone.

Before a prime mover can

cotract , the antagonist

must be equally relaxed.

muscle physiology through viewing electromyograms (EMGs) of muscles. Pump up your gestural

greeting with extra muscular effort so you can visualize/hear the EMG better. Can you use your

two EMGs to verify which muscle is the agonist when you flex your arm? How about when you

extend your arm?

B) The antagonist muscle might show spiking as well, why do you think? Try to explore your arm

motions until you can completely relax the antagonist (no spikes).

Fig. 24.14

Agonist- one muscle or group of muscles actively contract to produces

particular movement of a joint and is/are called a primary mover

or agonist. The agonist is the primarily responsible for producing

a movemet

Extensors working and

contracting as agonist

Flexor working and

contracting as agonist

Types of antagonistic movements

Antagonistic Muscles and Action

Muscle ActionFlexor muscle - flexes or bends a joint

Extensor muscle - extends or straightens a joint

Adductor muscle - moves parts of the body towards the midline of the body

Abductor muscle - moves parts of the body away from the midline of the body

Levator muscle - raises the body parts

Depressor muscle - lowers the body parts

Pronator muscle - rotates the forearm so that the palm of the hand is turned

towards the body

Supinator muscle - rotates the forearm so that the palm of the hand is turned away

from the body

Protractor muscle - draws parts forward or out

Retractor muscle - retracts body parts

Contractor muscle - surrounds orifices ( as gill , anus ) to close them

( sphinctor muscle )

Dilator muscle - surrounds orifices ( as gill , anus ) to open them

Directional terms

Types of antagonistic movements

Flexion and extension

Flexion and extension

Abduction and adduction

https://basicmedicalkey.com/to-clinically-oriented-anatomy/

Muscles and movements

The action associated with kicking a

soccer ball involves a number of

levers working together. Consider

the kicking motion shown on the

right.

Protractor muscles and its movements

Muscle fatigue

Muscle fatigue

Muscle fatigue is the physiological inability to contract ,

caused by an accumulation of lactic acid in the muscle.

During vigorous exercise,

Blood is unable to transport enough oxygen for the complete oxidation of glucose in the muscles.

In aerobic oxidation

Energy and pyruvic acid are released from sugar

The pyruvic acid is converted to carbon dioxide and waste.

However, in anaerobic oxidation ( insufficient oxygen )

the pyrubic acid is converted into lactic acid

Lactic acid normally leaves the muscle passing into blood stream

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Muscle fatigue ( reference )

- occurs when the muscles are no longer able to contract.

This condition is rare under most circumstances, because an individual will

stop their physical activity before true muscle fatigue sets in.

Marathon runners, however, will often collapse due to true muscle fatigue

since the extended period of physical activity severely depletes their energy

reserves.

( Reference )

In order to recover from typical exercise and from muscle fatigue, oxygen

levels must be restored in the muscle.

To return oxygen levels to normal, the respiratory system is signaled to

increase the depth and rate of respiration causing rapid, deep breathing.

During the recovery process, creatine phosphate (PCr) and glycogen

stores are regenerated, and any accumulated lactic acid is removed from

the muscles.

( Reference )

Muscle tone is accomplished by a complex interaction between the nervous

system and skeletal muscles that results in the activation of a few motor units.

Muscle tone - does not produce active movement

- but it keeps the muscles firm , healthy and ready to

respond stimulation

Muscle tone can be seen when muscles are in a state of slight

tension and they are ready for action.

Skeletal muscle tone

- stabilize the joints and maintain posture

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