PowerLecture: Chapter 6 The Muscular System. Learning Objectives Explain the structure of muscles,...

PowerLecture:PowerLecture:Chapter 6Chapter 6

The Muscular SystemThe Muscular System

Learning ObjectivesLearning Objectives

Explain the structure of muscles, from the Explain the structure of muscles, from the molecular level to the organ systems level.molecular level to the organ systems level.

Explain how biochemical events occur in Explain how biochemical events occur in muscle contractions and how antagonistic muscle contractions and how antagonistic muscle action refines movements.muscle action refines movements.

Explain the differences in stimulation Explain the differences in stimulation required for each type of muscle and how required for each type of muscle and how each responds.each responds.

Demonstrate how muscle disorders impact Demonstrate how muscle disorders impact the function of both the muscular and the function of both the muscular and skeletal systems.skeletal systems.

Impacts/IssuesImpacts/Issues

Pumping Up MusclesPumping Up Muscles


Can you bulk up your muscles by using a Can you bulk up your muscles by using a pill and do so safely?pill and do so safely?

Androstenedione and THG are available as Androstenedione and THG are available as supplements but are really steroid-like drugs supplements but are really steroid-like drugs unapproved by the FDA.unapproved by the FDA.

Another unapproved performance enhancer is Another unapproved performance enhancer is creatine, a substance normally produced by the creatine, a substance normally produced by the body during muscle activity.body during muscle activity.


The intricate movements of The intricate movements of

the human body are the the human body are the

result of interactions between result of interactions between

the skeleton and muscle.the skeleton and muscle.

How Would You Vote?How Would You Vote?To conduct an instant in-class survey using a classroom response To conduct an instant in-class survey using a classroom response system, access “JoinIn Clicker Content” from the PowerLecture main system, access “JoinIn Clicker Content” from the PowerLecture main menu. menu.

Dietary supplements are largely unregulated. Dietary supplements are largely unregulated. Should they be subject to more stringent Should they be subject to more stringent testing for effectiveness and safety?testing for effectiveness and safety? a. Yes, or companies could make any claim a. Yes, or companies could make any claim

about their product.about their product. b. No, so long as the extract does no harm, let b. No, so long as the extract does no harm, let

the buyer decide what to buy.the buyer decide what to buy.

Section 1Section 1

The Body’s Three Kinds The Body’s Three Kinds of Muscleof Muscle

The Body’s Three Kinds of MuscleThe Body’s Three Kinds of Muscle

The three kinds of muscle are built and The three kinds of muscle are built and function in different ways.function in different ways.

Skeletal muscleSkeletal muscle, composed of long thin cells , composed of long thin cells called muscle “fibers,” allows the body to move.called muscle “fibers,” allows the body to move.

Smooth muscleSmooth muscle is found in the walls of hollow is found in the walls of hollow organs and tubes; the cells are smaller than organs and tubes; the cells are smaller than those of skeletal muscle and are not striated.those of skeletal muscle and are not striated.

The heart is the only place where The heart is the only place where cardiac cardiac musclemuscle is found. is found.

Fig. 6.1, p.104Skeletal muscle

One skeletal muscle fiber

Fig. 6.1, p.104Smooth muscle

Smooth muscle fibers

Fig. 6.1, p.104Cardiac muscle

Cardiac muscle fibers

The Body’s Three Kinds of MuscleThe Body’s Three Kinds of Muscle

Cardiac muscle and smooth muscle are Cardiac muscle and smooth muscle are considered involuntary muscles because considered involuntary muscles because we cannot consciously control their we cannot consciously control their contraction; skeletal muscles are voluntary contraction; skeletal muscles are voluntary muscles.muscles.

Skeletal muscle comprises the body’s Skeletal muscle comprises the body’s muscular systemmuscular system..

© 2001 Brooks/Cole . Thomson©2005 Brooks/Cole . Thomson© 2007 - Thomson Higher Education

TRICEPS BRACHII

PECTORALIS MAJOR

SERRATUS ANTERIOR

EXTERNAL OBLIQUE

RECTUS ABDOMINUS

ADDUCTOR LONGUS

SARTORIUS

QUADRICEPS FEMORIS

TIBIALIS ANTERIOR

BICEPS BRACHII

DELTOID

TRAPIZIUS

LATISSIMUS DORSI

GLUTEUS MAXIMUS

BICEPS FEMORIS

GASTROCNEMIUS

Fig. 6.2, p.105

Fig. 6.20a, p.118

flexor digitorumsuperficialis

Fig. 6.20b, p.118

zygomaticus major

Section 2Section 2

The Structure and The Structure and Function of Skeletal Function of Skeletal

MusclesMuscles

A skeletal muscle is built of bundled muscle A skeletal muscle is built of bundled muscle cells.cells.

Inside each cell are threadlike Inside each cell are threadlike myofibrilsmyofibrils, , which are critical to muscle contraction.which are critical to muscle contraction.

The cells are bundled together with connective The cells are bundled together with connective tissue that extends past the muscle to form tissue that extends past the muscle to form tendonstendons, which attach the muscle to bones., which attach the muscle to bones.

The Structure and Function The Structure and Function of Skeletal Musclesof Skeletal Muscles

muscle

tendon(attached to bone)

tendon sheath

bone

Fig. 6.4, p.106

fluid

muscle’s outer sheath(connective tissue)

two bundles of muscle cells (each has its own connective tissue sheath)

one muscle cell

one myofibril

Fig. 6.3, p.106

Bones and skeletal muscles work like a Bones and skeletal muscles work like a system of levers. system of levers.

The human body’s skeletal muscles number The human body’s skeletal muscles number more than 600.more than 600.

The The originorigin end of each muscle is designated as end of each muscle is designated as being attached to the bone that moves being attached to the bone that moves relatively little; whereas the relatively little; whereas the insertioninsertion is is attached to the bone that moves the most. attached to the bone that moves the most.

Because most muscle attachments are located Because most muscle attachments are located close to joints, only a small contraction is close to joints, only a small contraction is needed to produce considerable movement of needed to produce considerable movement of some body parts (leverage advantage).some body parts (leverage advantage).


Many muscles are arranged as pairs or in Many muscles are arranged as pairs or in groups.groups.

Many muscles are arranged as pairs or Many muscles are arranged as pairs or grouped for related function.grouped for related function.

• Some work Some work antagonisticallyantagonistically (in opposition) so that (in opposition) so that one reverses the action of the other.one reverses the action of the other.

• Others work Others work synergisticallysynergistically, the contraction of one , the contraction of one stabilizes the contraction of another.stabilizes the contraction of another.

Reciprocal innervationReciprocal innervation dictates that only one dictates that only one muscle of an antagonistic pair (e.g. biceps and muscle of an antagonistic pair (e.g. biceps and triceps) can be stimulated at a time.triceps) can be stimulated at a time.


triceps relaxes

biceps contracts at the same time, and pulls forelimb up

triceps contracts,pulls the forelimbdown

at the same time, biceps relaxes

Fig. 6.5, p.107

origin

insertion

““Fast” and “slow” muscle.Fast” and “slow” muscle. Humans have two general types of skeletal Humans have two general types of skeletal

muscles:muscles:• ““Slow” muscle is red in color due to myoglobin and Slow” muscle is red in color due to myoglobin and

blood capillaries; its contractions areblood capillaries; its contractions are slower but slower but more sustained.more sustained.

• ““Fast” or “white” muscle cells contain fewer Fast” or “white” muscle cells contain fewer mitochondria and less myoglobin but can contract mitochondria and less myoglobin but can contract rapidly and powerfully for short periods.rapidly and powerfully for short periods.


Fig. 6.6, p.107

When athletes train, one goal is to increase the When athletes train, one goal is to increase the relative size and contractile strength of fast relative size and contractile strength of fast (sprinters) and slow (distance swimmers) muscle (sprinters) and slow (distance swimmers) muscle fibers.fibers.

Figure 6.6bFigure 6.6b


Section 3Section 3

How Muscles ContractHow Muscles Contract

How Muscles ContractHow Muscles Contract A muscle contracts when its cells shorten.A muscle contracts when its cells shorten.

Muscles are divided into contractile units called Muscles are divided into contractile units called sarcomeressarcomeres..

Each muscle cell contains myofibrils composed Each muscle cell contains myofibrils composed of thin (of thin (actinactin) and thick () and thick (myosinmyosin) filaments.) filaments.

• Each actin filament is actually two beaded strands of Each actin filament is actually two beaded strands of protein twisted together.protein twisted together.

• Each myosin filament is a protein with a double head Each myosin filament is a protein with a double head (projecting outward) and a long tail (which is bound (projecting outward) and a long tail (which is bound together with others).together with others).

The arrangement of actin and myosin filaments The arrangement of actin and myosin filaments gives skeletal muscles their characteristic gives skeletal muscles their characteristic striped appearance.striped appearance.

Fig. 6.8, p.108

part of a thin filament

part of a thick filament

part of a myosin molecule

one actin molecule

a Arrangement of actin molecules in the thin filaments

b Arrangement of myosin molecules in the thick filaments

Fig. 6.7a, p.108

One myofibril inside cell:

a. Skeletal muscle cell, longitudinal section. All bands of its myofibrils are in register and give the cell a striped appearance.

Z band Z bandZ band H zone

I band I bandA band

sarcomere sarcomere

Fig. 6.7b, p.108

b. Sarcomeres. Manythick and thin filamentsoverlap in an A band.Only thick filamentsextend across the Hzone. Only thin filamentsextend across I bandsto the Z bands.


Muscle cells shorten when actin filaments Muscle cells shorten when actin filaments slide over myosin.slide over myosin. Within each sarcomere there are two sets of Within each sarcomere there are two sets of

actin filaments, which are attached on opposite actin filaments, which are attached on opposite sides of the sarcomere; myosin filaments lie sides of the sarcomere; myosin filaments lie suspended between the actin filaments.suspended between the actin filaments.

Fig. 6.9, p.109

actin myosin actin

Sarcomere when muscle cell is relaxed

Same sarcomere, contracted

a

b

myosinactin actin

p.116


During contraction, the myosin filaments During contraction, the myosin filaments physically slide along and pull the two sets of physically slide along and pull the two sets of actin filaments toward each other at the center actin filaments toward each other at the center of the sarcomere; this is called the of the sarcomere; this is called the sliding-sliding-filament modelfilament model of contraction. of contraction.

• When a myosin head is energized, it forms cross-When a myosin head is energized, it forms cross-bridges with an adjacent actin filament and tilts in a bridges with an adjacent actin filament and tilts in a power stroke toward the sarcomere’s center.power stroke toward the sarcomere’s center.

• Energy from ATP drives the power stroke as the Energy from ATP drives the power stroke as the heads pull the actin filaments along.heads pull the actin filaments along.

• After the power stroke the myosin heads detach and After the power stroke the myosin heads detach and prepare for another attachment (power stroke).prepare for another attachment (power stroke).

Fig. 6.9cd, p. 109

myosin head

one of many myosin binding sites on actin

cross bridgecross bridge

Fig. 6.9ef, p. 109

ATPATP

Fig. 6.9g, p. 109


When a person dies, ATP production stops, When a person dies, ATP production stops, myosin heads become stuck to actin, and myosin heads become stuck to actin, and rigor rigor mortismortis sets in, making the body stiff. sets in, making the body stiff.

Section 4Section 4

How the Nervous How the Nervous System Controls Muscle System Controls Muscle

Contraction Contraction

Calcium ions are the key to contraction.Calcium ions are the key to contraction. Skeletal muscles contract in response to Skeletal muscles contract in response to

signals from motor neurons of the nervous signals from motor neurons of the nervous system.system.

• Signals arrive at the Signals arrive at the T tubulesT tubules of the of the sarcoplasmic sarcoplasmic reticulum reticulum ((SRSR)),, which wraps around the myofibrils. which wraps around the myofibrils.

• The SR responds by releasing stored calcium ions; The SR responds by releasing stored calcium ions; calcium binds to the protein calcium binds to the protein troponintroponin, changing the , changing the conformation of actin and allowing myosin cross-conformation of actin and allowing myosin cross-bridges to form.bridges to form.

• Another protein, Another protein, tropomyosintropomyosin, is also associated , is also associated with actin filaments.with actin filaments.

How the Nervous System How the Nervous System Controls Muscle ContractionControls Muscle Contraction

When nervous stimulation stops, calcium ions When nervous stimulation stops, calcium ions are actively taken up by the sarcoplasmic are actively taken up by the sarcoplasmic reticulum and the changes in filament reticulum and the changes in filament conformation are reversed; the muscle relaxes.conformation are reversed; the muscle relaxes.


© 2007 Thomson Higher Education

Fig. 6.10, p. 110

section from spinal cordmotor neuron

Signals from the nervous system

Endings of motor neuron

section from a skeletal muscle

part of one muscle cell

Z line

one of the myofibrils inside the muscle fiber

plasma membrane of skeletal muscle fiber

sarcoplasmic reticulum(calcium in storage)T tubule

Z line

a

b

c

d

Signals travel along muscle cell’s plasma membrane to sarcoplasmic reticulum around myofibrils.

Signals trigger the release of calcium ions from sarcoplasmic reticulum threading among the myofibrils.

Fig. 6.11, p. 111

troponin

a Actin molecule

myosin binding site blocked

b Cross-section of (a). Red dots are calcium ions bound to troponin (green).

c Calcium ions flow in; troponin binds additional calcium.

f Cross-bridge forms betweenactin and myosin.

d Troponin changes shape,moving away from the myosin binding site.

e The binding site is now exposed; actin can bind the myosin head.

myosin head

myosin head

cross-bridge

troponin

a Actin molecule

myosinbinding siteblocked

Fig. 6.11a.c, p.111

b Cross-section of (a). Red dots are calcium ions bound to troponin (green).

c Calcium ions flow in; troponinbinds additional calcium.

myosin head

myosin head

Fig. 6.11d.f, p.111

f Cross-bridge forms betweenactin and myosin.

d Troponin changes shape,moving away from the myosin binding site.

e The binding site is now exposed; actin can bind the myosin head.

Neurons act on muscle cells at Neurons act on muscle cells at neuromuscular junctions. neuromuscular junctions.

At At neuromuscular junctionsneuromuscular junctions, impulses from , impulses from the branched endings (axons) of motor neurons the branched endings (axons) of motor neurons pass to the muscle cell membranes.pass to the muscle cell membranes.

• Between the axons and the muscle cell is a gap Between the axons and the muscle cell is a gap called a called a synapsesynapse..

• Signals are transmitted across the gap by a Signals are transmitted across the gap by a neurotransmitterneurotransmitter called called acetylcholineacetylcholine (ACh). (ACh).

When the neuron is stimulated, calcium When the neuron is stimulated, calcium channels open to allow calcium ions to flow channels open to allow calcium ions to flow inward, causing a release of acetylcholine into inward, causing a release of acetylcholine into the synapse.the synapse.


Fig. 6.12, p.111Muscle cell receptor for ACh

Axon ending ofmotor neuron

Muscle cell

Vesicles containing ACh molecules

Synapse

Section 5Section 5

How Muscle Cells Get How Muscle Cells Get EnergyEnergy

How Muscle Cells Get EnergyHow Muscle Cells Get Energy

ATP supplies the energy for muscle ATP supplies the energy for muscle contraction.contraction.

Initiation of muscle contraction requires much Initiation of muscle contraction requires much ATP; this will initially be provided by ATP; this will initially be provided by creatinecreatine phosphatephosphate,, which gives up a phosphate to which gives up a phosphate to ADP to make ATP.ADP to make ATP.

Cellular respiration provides most of the ATP Cellular respiration provides most of the ATP needed for muscle contraction after this, even needed for muscle contraction after this, even during the first 5-10 minutes of moderate during the first 5-10 minutes of moderate exercise.exercise.

How Muscle Cells Get EnergyHow Muscle Cells Get Energy

During prolonged muscle action, glycolysis During prolonged muscle action, glycolysis alone produces low amounts of ATP; lactic acid alone produces low amounts of ATP; lactic acid is also produced, which hinders further is also produced, which hinders further contraction.contraction.

Muscle fatigueMuscle fatigue is due to the is due to the oxygen debtoxygen debt that results when muscles use more ATP that results when muscles use more ATP than cellular respiration can deliver.than cellular respiration can deliver.

Pathway 1Phosphate Transferred from

Creatine Phosphate

Pathway 2Aerobic

Respiration

Pathway 3Glycolysis

Alone

creatine

oxygen glucose from bloodstream and from glycogen breakdown in cells

ADP + Pi

Relaxation

Contraction

Fig. 6.13, p. 112

ATP

Section 6Section 6

Properties of Whole Properties of Whole MusclesMuscles

Properties of Whole MusclesProperties of Whole Muscles

Several factors determine the Several factors determine the characteristics of a muscle contraction.characteristics of a muscle contraction.

A A motor neuronmotor neuron and the muscle cells under its and the muscle cells under its control are a control are a motor unitmotor unit; the number of cells in ; the number of cells in a motor unit depends on the precision of the a motor unit depends on the precision of the muscle control needed.muscle control needed.

• A single, brief stimulus to a motor unit causes a brief A single, brief stimulus to a motor unit causes a brief contraction called a contraction called a muscle twitchmuscle twitch..

• Repeated stimulation makes the twitches run Repeated stimulation makes the twitches run together in a sustained contraction called together in a sustained contraction called tetanustetanus ((tetanytetany))..

slice from spinal cord

motor neuron leading from spinal cord to muscle fibers

neuromuscular junction

motor unit

Fig. 6.14a, p. 112

repeated stimulation

tetanic contraction

twitch

six stimulations per second

stimulus contraction

relaxation starts

Fig. 6.15ac, p.113Time

Fo

rce

Fo

rce

Fo

rce


Not all muscle cells in a muscle contract at the Not all muscle cells in a muscle contract at the same time.same time.

• The number of motor units that are activated The number of motor units that are activated determines the strength of the contraction: Small determines the strength of the contraction: Small number of units = weak contraction; large number of number of units = weak contraction; large number of units at greater frequency = stronger contraction.units at greater frequency = stronger contraction.

• Muscle toneMuscle tone is the continued steady, low level of is the continued steady, low level of contraction that stabilizes joints and maintains contraction that stabilizes joints and maintains general muscle health.general muscle health.


Muscle tensionMuscle tension is the force a contracting is the force a contracting muscle exerts on an object; to contract, a muscle exerts on an object; to contract, a muscle’s tension must exceed the load muscle’s tension must exceed the load opposing it.opposing it.

• An An isotonicallyisotonically contracting muscle shortens and contracting muscle shortens and moves a loadmoves a load

• An An isometricallyisometrically contracting muscle develops contracting muscle develops tension but does not shorten.tension but does not shorten.

contractedmuscle canshorten

contractedmuscle can’tshorten

Fig. 6.16, p. 113


Tired muscles can’t generate much force.Tired muscles can’t generate much force. Muscles Muscles fatiguefatigue when strong stimulation keeps when strong stimulation keeps

a muscle in a state of tetanus too long.a muscle in a state of tetanus too long. After resting, muscles will be able to contract After resting, muscles will be able to contract

again; muscles may need to rest for minutes up again; muscles may need to rest for minutes up to a day to fully recover. to a day to fully recover.

Section 7Section 7

Muscle DisordersMuscle Disorders


Strains and tears are muscle injuries.Strains and tears are muscle injuries. Muscle Muscle strainsstrains come from movement that come from movement that

stretches or tears muscle fibers; ice, rest and stretches or tears muscle fibers; ice, rest and anti-inflammatory drugs (ibuprofen) allow anti-inflammatory drugs (ibuprofen) allow damage to repair.damage to repair.

If the whole muscle is torn, If the whole muscle is torn, scar tissue may develop, scar tissue may develop, shortening the muscle and shortening the muscle and making it function less making it function less effectively.effectively.

Figure 6.17Figure 6.17


Sometimes a skeletal muscle will contract Sometimes a skeletal muscle will contract abnormally.abnormally.

A muscle A muscle spasmspasm is a sudden, involuntary is a sudden, involuntary contraction that rapidly releases, while contraction that rapidly releases, while crampscramps are spasms that don’t immediately release; are spasms that don’t immediately release; cramps usually occur in calf and thigh muscles.cramps usually occur in calf and thigh muscles.

TicsTics are minor, involuntary twitches of muscles are minor, involuntary twitches of muscles in the face and eyelids.in the face and eyelids.


Muscular dystrophies destroy muscle fibers.Muscular dystrophies destroy muscle fibers. Muscular dystrophiesMuscular dystrophies are genetic diseases are genetic diseases

leading to breakdown of muscle fibers over leading to breakdown of muscle fibers over time.time.

• Duchenne muscular Duchenne muscular

dystrophydystrophy (DMD) is (DMD) is

common in children; a common in children; a

single mutant gene single mutant gene

interferes with interferes with

sarcomere contraction.sarcomere contraction.

Figure 6.18Figure 6.18


• Myotonic muscular dystrophyMyotonic muscular dystrophy is usually found in is usually found in adults; muscles of the hands and feet contract strongly adults; muscles of the hands and feet contract strongly but fail to relax normally.but fail to relax normally.

In these diseases, muscles progressively weaken In these diseases, muscles progressively weaken and shrivel.and shrivel.

Exercise makes the most of muscles.Exercise makes the most of muscles. Muscles that are damaged or which go unused Muscles that are damaged or which go unused

for prolonged periods of time will for prolonged periods of time will atrophyatrophy (waste (waste away).away).


Aerobic exerciseAerobic exercise improves the capacity of improves the capacity of muscles to do work.muscles to do work.

• Walking, biking, and jogging are examples of Walking, biking, and jogging are examples of exercises that increase endurance.exercises that increase endurance.

• Regular aerobic exercise increases the number and Regular aerobic exercise increases the number and size of mitochondria, the number of blood capillaries, size of mitochondria, the number of blood capillaries, and the amount of myoglobin in the muscle tissue.and the amount of myoglobin in the muscle tissue.

Figure 6.19aFigure 6.19a


Strength trainingStrength training improves function of fast improves function of fast muscle but does not increase endurance.muscle but does not increase endurance.

Even modest activity slows the loss of muscle Even modest activity slows the loss of muscle strength that comes with aging.strength that comes with aging.

Figure 6.19bFigure 6.19b

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