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Hole’s Human

Anatomy and Physiology Eleventh Edition

Shier w Butler w Lewis

Chapter

9

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Functions of Muscular System

• Movement

• Posture Maintenance

• Joint Stability

• Heat Generation

2

Three Types of Muscle Tissue

3

Skeletal Muscle • usually attached to

bones

• under conscious control

• striated

Smooth Muscle • walls of most viscera, blood

vessels, skin

• not under conscious control

• not striated

Cardiac Muscle • wall of heart

• not under conscious

control

• striated

Structure of a Skeletal Muscle

4

Composed of:

- skeletal muscle tissue

- nervous tissue

- blood

- connective tissues

• fascia

• tendons

• aponeuroses

Skeletal Muscle Structure

5

•Muscle cells called

muscle fibers wrapped

in endomysium

• Bundles of muscle

fibers called fasicles

wrapped in perimysium

•Many fasicles make a

muscle and are wrapped

in epimysium

Skeletal Muscle Fiber Structure

6

• Muscle fibers are long, thin cells made of myofibrils

• Myofibrils composed of 2 types of cytoskeleton

•Myosin – thick protein filaments

•Actin – thin protein filaments

Skeletal Muscle Fibers

7

• sarcolemma - cell membrane

• sacroplasm – cell cytoplasm

• sarcoplasmic reticulum – endoplasmic reticulum

• transverse tubule - channel that is continuous with

sarcolemma and extends into sarcoplasm

Sarcomere: Unit of contraction

8

• I bands – light area = actin only

• A bands – dark area = overlapping actin and myosin

• Z lines – dividing line between individual sarcomeres

Special Features of Myofilaments

9

Thick Filaments = Myosin

• cross-bridges

Thin Filaments = Actin

• associated with

troponin and tropomyosin

Neuromuscular Junction

10

Site where an axon

and muscle fiber meet

• motor neuron

• motor end plate

• synapse

• synaptic cleft

• synaptic vesicles

• neurotransmitters

Motor Unit

11

• single motor neuron

• all muscle fibers

controlled by motor

neuron

Stimulus for Contraction

12

• acetylcholine (ACh)

• nerve impulse causes

release of ACh from

synaptic vesicles

• ACh binds to ACh

receptors on motor end

plate

• generates a muscle

impulse

Excitation Contraction Coupling

13

• muscle impulses cause

sarcoplasmic reticulum

to release calcium ions

into cytosol

• calcium binds to

troponin to change its

shape

Excitation Contraction Coupling

14

• position of

tropomyosin is altered

• binding sites on

actin are exposed

• actin and myosin

molecules bind

Sliding Filament Model of Muscle

Contraction

15

When cross-bridges

pull on actin the

sarcromeres shorten,

thick and thin

filaments slide past

one another

Cross-bridge Cycling

16

When myosin is pulling

on the actin, ATP is

broken down into ADP

and phosphate.

Relaxation

17

acetylcholinesterase – enzyme that rapidly

decomposes acetylcholine remaining in the synapse

As a result:

• muscle impulse stops

• stimulus to sarcolemma and muscle fiber membrane

ceases

• calcium moves back into sarcoplasmic reticulum

• myosin and actin binding prevented

• muscle fiber relaxes

Major Events of Muscle Contraction

and Relaxation

18

Energy Sources for Contraction

19

• creatine phosphate – stores energy that quickly

converts ADP to ATP

1) Creatine phosphate 2) Cellular respiration

Oxygen Supply and

Cellular Respiration

20

• Anaerobic Phase • glycolysis

• occurs in cytoplasm

• produces little ATP

• Aerobic Phase • citric acid cycle

• electron transport chain

• occurs in the

mitochondria

• produces most ATP • myoglobin stores extra

oxygen

Oxygen Debt

21

• oxygen not available

• glycolysis continues

• pyruvic acid

•converted to lactic acid

• liver converts lactic

acid to glucose

Oxygen debt – amount of oxygen needed by liver cells

to use the accumulated lactic acid to produce glucose

Muscle Fatigue

22

• inability to contract

• commonly caused from

• decreased blood flow

• ion imbalances across the sarcolemma

• accumulation of lactic acid

• cramp – sustained, involuntary muscle contraction

Heat Production

23

• by-product of cellular respiration

• muscle cells are major source of body heat

• blood transports heat throughout body

Muscular Responses

24

Threshold Stimulus

• minimal strength required to cause contraction

Recording a Muscle

Contraction

• twitch

• latent period

• period of contraction

• period of relaxation

• refractory period

• all-or-none response

Summation

25

• process by which individual twitches combine

• produces sustained contractions

• can lead to tetanic contractions

Recruitment of Motor Units

26

• recruitment - increase in the number of motor units

activated

• whole muscle composed of many motor units

• more precise movements are produced with fewer

muscle fibers within a motor unit

• as intensity of stimulation increases, recruitment of

motor units continues until all motor units are

activated

Sustained Contractions

27

• smaller motor units (smaller diameter axons)

- recruited first

• larger motor units (larger diameter axons)

- recruited later

• produce smooth movements

• muscle tone – continuous state of partial contraction

Types of Contractions

28

• isotonic – muscle contracts

and changes length

• isometric – muscle contracts but

does not change length

Fast and Slow Twitch

Muscle Fibers

29

Slow-twitch fibers (type I)

• always oxidative

• resistant to fatigue

• red fibers

• most myoglobin

• good blood supply

• many mitochodria

•“dark meat”

Fast-twitch glycolytic fibers (type IIa)

• white fibers (less myoglobin)

• poorer blood supply

• susceptible to fatigue

•“white meat”

Fast-twitch fatigue-resistant

fibers (type IIb)

• intermediate fibers

• oxidative

• intermediate amount of

myoglobin

• pink to red in color

•resistant to fatigue

Smooth Muscle Fibers

30

Compared to skeletal muscle fibers

• shorter

• single, centrally located nucleus

• elongated with tapering ends

• myofilaments randomly organized

• lack striations

• lack transverse tubules

• sarcoplasmic reticula not well developed

• 2 types

•Visceral – walls of hollow organs

• Multiunit – iris of eye & blood vessesels

Smooth Muscle Contraction

31

• Resembles skeletal muscle contraction • interaction between actin and myosin

• both use calcium and ATP

• both are triggered by membrane impulses

• Different from skeletal muscle contraction • smooth muscle lacks troponin (replaced with calmodulin)

• two neurotransmitters (acetlycholine and norepinephrine)

affect smooth muscle

• hormones affect smooth muscle

• stretching can trigger smooth muscle contraction

• smooth muscle slower to contract and relax

• smooth muscle more resistant to fatigue

Cardiac Muscle

32

• located only in the heart

• muscle fibers joined together by intercalated discs

• fibers branch

• network of fibers contracts as a unit

• self-exciting and rhythmic

• longer refractory period than skeletal muscle

Characteristics of Muscle Tissue

33

Skeletal Muscle Actions

34

• origin – immovable end

• insertion – movable end

• prime mover (agonist) –

primarily responsible for

movement

• synergists – assist prime

mover

• antagonist – resist prime

mover’s action and cause

movement in the opposite

direction

Body Movement

35

Four Basic Components of Lever

1. rigid bar – bones

2. fulcrum – point on which bar moves; joint

3. object - moved against resistance; weight

4. force – supplies energy for movement; muscles

Levers and Movement

36

Life-Span Changes

37

• myoglobin, ATP, and creatine phosphate

decline

• by age 80, half of muscle mass has

atrophied

• adipose cells and connective tissues

replace muscle tissue

• exercise helps to maintain muscle mass

and function

Clinical Application

38

Myasthenia Gravis

• autoimmune disorder

• receptors for ACh on muscle cells are attacked

• weak and easily fatigued muscles result

• difficulty swallowing and chewing

• ventilator needed if respiratory muscles are affected

• treatments include

• drugs that boost ACh

• removing thymus gland

• immunosuppressant drugs

• antibodies

More Clinical Applications

39

• Moebius Syndrome

• “walking corpse syndrome” or

“stone face”

•Tendinitis

• Muscular Dystrophy

•Poliomyelitis

•Tetanus and Botulism

•Lou Gehrig's disease

• amyotrophic lateral sclerosis (ALS)

Major Skeletal Muscles

40

Major Skeletal Muscles

41

Muscles of Facial Expression

42

Muscles of Mastication

43

Muscles of Facial Expression and

Mastication

44

Muscles That Move the Head and

Vertebral Column

45

Muscles That Move the Head

and Vertebral Column

46

Muscles That Move the Pectoral

Girdle

47

Muscles That Move the Pectoral

Girdle

48

Muscles That Move the Arm

49


50


51

Muscles That Move the Forearm

52


53


54

Cross Section of the Forearm

55

Muscles That Move the Hand

56

Muscles That Move the Hand

57

Muscles of the Abdominal Wall

58

Muscles of the Abdominal Wall

59

Muscles of the Pelvic Outlet

60

Muscles of Pelvic Outlet

61

Muscles That Move the Thigh

62


63


64

Muscles That Move the Leg

65


66


67


68

Muscles That Move the Foot

69


70


71

Cross-bridge Cycling

72

• myosin cross-bridge attaches

to actin binding site

• myosin cross-bridge pulls

thin filament

•ADP and phosphate

released from myosin

• new ATP binds to

myosin

• linkage between actin

and myosin cross-bridge

break

•ATP splits

•myosin cross-bridge goes back

to original position

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