PowerPoint Lecture Outlines

to accompany

1

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

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Three Types of Muscle Tissue

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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

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Composed of:

- skeletal muscle tissue

- nervous tissue

- blood

- connective tissues

• fascia

• tendons

• aponeuroses

Skeletal Muscle Structure

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•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

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• 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

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• 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

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• 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

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Thick Filaments = Myosin

• cross-bridges

Thin Filaments = Actin

• associated with

troponin and tropomyosin

Neuromuscular Junction

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Site where an axon

and muscle fiber meet

• motor neuron

• motor end plate

• synapse

• synaptic cleft

• synaptic vesicles

• neurotransmitters

Motor Unit

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• single motor neuron

• all muscle fibers

controlled by motor

neuron

Stimulus for Contraction

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• 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

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• muscle impulses cause

sarcoplasmic reticulum

to release calcium ions

into cytosol

• calcium binds to

troponin to change its

shape

Excitation Contraction Coupling

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• position of

tropomyosin is altered

• binding sites on

actin are exposed

• actin and myosin

molecules bind

Sliding Filament Model of Muscle

Contraction

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When cross-bridges

pull on actin the

sarcromeres shorten,

thick and thin

filaments slide past

one another

Cross-bridge Cycling

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When myosin is pulling

on the actin, ATP is

broken down into ADP

and phosphate.

Relaxation

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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

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Energy Sources for Contraction

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• creatine phosphate – stores energy that quickly

converts ADP to ATP

1) Creatine phosphate 2) Cellular respiration

Oxygen Supply and

Cellular Respiration

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• 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

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• 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

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• 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

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• by-product of cellular respiration

• muscle cells are major source of body heat

• blood transports heat throughout body

Muscular Responses

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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

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• process by which individual twitches combine

• produces sustained contractions

• can lead to tetanic contractions

Recruitment of Motor Units

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• 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

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• 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

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• isotonic – muscle contracts

and changes length

• isometric – muscle contracts but

does not change length

Fast and Slow Twitch

Muscle Fibers

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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

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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

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• 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

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• 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

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Skeletal Muscle Actions

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• 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

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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

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Life-Span Changes

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• 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

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• 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

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Major Skeletal Muscles

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Muscles of Facial Expression

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Muscles of Mastication

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Muscles of Facial Expression and

Mastication

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Muscles That Move the Head and

Vertebral Column

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Muscles That Move the Head

and Vertebral Column

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Muscles That Move the Pectoral

Girdle

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Muscles That Move the Pectoral

Girdle

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Muscles That Move the Arm

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Muscles That Move the Arm

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Muscles That Move the Arm

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Muscles That Move the Forearm

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Muscles That Move the Forearm

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Muscles That Move the Forearm

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Cross Section of the Forearm

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Muscles That Move the Hand

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Muscles That Move the Hand

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Muscles of the Abdominal Wall

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Muscles of the Abdominal Wall

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Muscles of the Pelvic Outlet

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Muscles of Pelvic Outlet

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Muscles That Move the Thigh

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Muscles That Move the Thigh

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Muscles That Move the Thigh

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Muscles That Move the Leg

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Muscles That Move the Leg

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Muscles That Move the Leg

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Muscles That Move the Leg

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Muscles That Move the Foot

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Muscles That Move the Foot

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Muscles That Move the Foot

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Cross-bridge Cycling

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• 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