Visualizing A&P Sample Chapter

6Body-building and body-sculpting both build up muscles in selected

areas of the body, resulting in a gener-ally pleasing shape or appearance. Muscle makes up almost 40–50% of the total mass of your body. Many of these primary engines of motion are intimately linked to the skeletal system, but there are many muscles that you don’t even think about. For example, smooth muscle tissue forms the walls of your blood vessels, gastrointestinal tract, and urinary bladder, helps control blood pressure, circulate blood, move food through the digestive tract, and receive and store urine for periods of time. Your heart, made of cardiac muscle tissue, works constantly throughout your life, without a rest.

Muscle is one of the few tissue types that you can actually modify, but how? The answer is through rigor-ous and regular exercise. You can change the size and type of muscle fibers (cells), thereby increasing strength and endurance. In fact, your muscle mass readily adjusts to your lifestyle and exercise regimen. People with active lifestyles tend to have more muscle mass than sedentary individuals. Patients on long-term bed rest tend to lose muscle mass quickly. Maintaining your muscle health is important to maintaining your overall health.

Let’s take a closer look at these remarkable tissues.

The Muscular System

152

Chapter OutlineThe Body Contains Three Types of Muscular Tissues 154

• SkeletalMuscleTissueIsAttachedtotheBones• CardiacMuscleTissueIsFoundOnlyintheHeart• SmoothMuscleTissueIsFoundinMostBodyOrgans

Muscles Are Built to Move 156• MusclesAreComposedofBundlesofMuscleFibers• TheSlidingFilamentTheoryExplainsMuscle

Contraction• NerveSignalsInitiatetheContractionofSkeletal

Muscle• MuscleContractionComesinManyForms:Twitch,

Tetanus,Isotonic,andIsometric

Smooth Muscle Tissue Is in the Walls of Most Organs 165

• SmoothMuscleTissueLooksVeryDifferentfromSkeletalMuscleTissue

• SmoothMuscleTissueComesinTwoVarieties:VisceralandMulti-Unit

Cardiac Muscle Tissue Forms the Muscular Wall of the Heart 167

Skeletal Muscles Are Grouped Based on Location and Action 168

• SkeletalMusclesWorkinGroups■ WhataHealthProviderSees:ExerciseMaintains

HealthyMuscles• MusclesoftheHeadandNeckControlFacial

Expressions,AllowYoutoSpeakandChew,andEnableYourEyestoOpen,Close,andMove

• MusclesoftheThorax,Abdomen,Neck,andBackPerformManyFunctions

• MusclesoftheShoulderandUpperLimbAreConcernedwithMovement

• MusclesoftheLowerBodyMovetheThighandLegs

✓✓Chapter planner

❑ Studythepictureandreadtheopeningstory.

❑ ScantheLearningObjectivesineachsection:p.154❑ p.156❑ p.165❑ p.167❑ p.168❑

❑ Readthetextandstudyallvisuals.Answeranyquestions.

Analyze key features

❑ InSight,pp.156–157❑

❑ ProcessDiagram,p.159❑ p.160❑ p.161❑

❑ WhataHealthProviderSees,p.169❑

❑ Stop:AnswertheConceptChecksbeforeyougoon:p.155❑ p.165❑ p.166❑ p.167❑ p.184❑

End of chapter

❑ ReviewtheSummaryandKeyTerms.

❑ AnswertheCriticalandCreativeThinkingQuestions.

❑ AnswerWhatishappeninginthispicture?

❑ CompletetheSelf-Testandcheckyouranswers.

154 CHAPTER 6 The Muscular System

Stomach

Epithelialtissue

Serousmembrane

Smooth muscletissue layers

Nucleus

Striations

Skeletal musclefiber

Longitudinal section of skeletal muscle tissue

a. Skeletal muscle tissue

400xLM

Striations

Nucleus

Heart

Cardiac muscle fiber(cell)

Longitudinal section of cardiac muscle tissue

500x

Intercalateddisc

LM

Nucleus of smooth muscle fiber

Longitudinal section of smooth muscle tissue

500x

Smooth muscle fiber

LM

c. Smooth muscle tissue

b. Cardiac muscle tissue

Cardiac muscle fibers

Branched cylindrical fiber (cell), usually with one centrally located nucleus; intercalated discs join neighboring fibers; striated

Fiber (cell) is thickest in the middle, tapered at each end, has one centrally located nucleus; not striated

Skeletal muscle fiber

Smooth muscle fiber

Long cylindrical fiber (cell) with many peripherally located nuclei; striated; unbranched

The Body Contains Three Types of Muscular TissueslearninG OBJeCtiVeS1. Describe the types of muscular tissue.2. list the various locations of the types of muscu-

lar tissue.3. Outline the functions of muscular tissue.

M uscle accounts for 40–50 percent of your body mass. Muscle allows the body to move around in its environment or the organs to move within the body. Compared to other tissues in

the body, muscular tissue has a limited capacity to divide and regenerate. There are three types of muscular tissue (Figure 6.1): skeletal, cardiac, and smooth.

Types of muscular tissue • Figure 6.1

Musculartissuesconsistofthreetypes.

A s k Yo u r s e l f

Whichtypeofmuscletissueiscomposedofstriatedcellsthatareinterconnectedbyintercalateddiscs?

a.Smoothmuscleb.Skeletalmusclec.Cardiacmuscle

Skeletal Muscle tissue is attached to the BonesThere are about 700 skeletal muscles in your body. Skeletal muscles produce body movements, stabilize the skeleton, and produce much of the heat that helps main-tain body temperature. Movements of skeletal muscle can be voluntary—you can knowingly contract and relax them—or involuntary. Skeletal muscle tissue is banded, or striated; the striations can be seen only under a mi-croscope. The ability of skeletal muscle to regenerate is somewhat limited and involves satellite cells, a type of stem cell that becomes activated to form new skeletal muscle cells.

The Body Contains Three Types of Muscular Tissues 155

Cardiac Muscle tissue is Found Only in the heartCardiac muscle tissue makes up the walls of the heart and generates the force necessary to pump your blood. Cardiac muscle contractions are involuntary: You don’t think about contracting and relaxing this muscle. Unlike most other muscle tissue, cardiac muscle tissue has the ability to contract without the assistance of the nervous system. Like skeletal muscle, cardiac muscle is striated. The regeneration ability of cardiac muscle is minimal.

Smooth Muscle tissue is Found in Most Body OrgansSmooth muscle tissue forms the walls of hollow organs such as blood vessels, airways, the stomach, the intestines, and the uterus. The smooth muscle of these organs helps to store and move substances within the body and regu-

lates organ volume. Smooth muscle cells are considerably smaller than other muscle cells and are not striated. Like cardiac muscle, the contraction and relaxation of smooth muscle is involuntary. Of the three types of musclar tissue, smooth muscle tissue regenerates most easily, most likely because this type of muscle has a less complex structure than that of the striated cardiac or skeletal muscle tissues.

1. Which type of muscular tissue is striated and voluntary?

2. What type of muscular tissue will an obstetri-cian be cutting through to deliver a baby via cesarean section?

3. Which types of muscular tissue play a role in generating body heat?

Stomach

Epithelialtissue

Serousmembrane

Smooth muscletissue layers

Nucleus

Striations

Skeletal musclefiber

Longitudinal section of skeletal muscle tissue

a. Skeletal muscle tissue

400xLM

Striations

Nucleus

Heart

Cardiac muscle fiber(cell)

Longitudinal section of cardiac muscle tissue

500x

Intercalateddisc

LM

Nucleus of smooth muscle fiber

Longitudinal section of smooth muscle tissue

500x

Smooth muscle fiber

LM

c. Smooth muscle tissue

b. Cardiac muscle tissue


Branched cylindrical fiber (cell), usually with one centrally located nucleus; intercalated discs join neighboring fibers; striated

Fiber (cell) is thickest in the middle, tapered at each end, has one centrally located nucleus; not striated


Smooth muscle fiber

Long cylindrical fiber (cell) with many peripherally located nuclei; striated; unbranched

156

3. Outline the sequence of events of skeletal mus-cle contraction (excitation–contraction coupling).

4. associate the type of muscle fiber (cell) with the source of energy in given situations.

Muscles Are Built to MovelearninG OBJeCtiVeS1. Describe the structure of skeletal muscle

tissue.2. explain how skeletal muscle tissue shortens.

InSight The structure of a skeletal muscle and its connective tissue coverings: A macroscopic view • Figure 6.2

Transverseplane

Tendon Bone

Fascicle

Transverse sections

Periosteum

Tendon

Skeletal muscle

Perimysium

Epimysium

Fascicle

Musclefiber (cell)

Muscle fiber

Myofibril

Perimysium

Perimysium

Endomysium

Sarcoplasm

Sarcolemma

Filament

Nucleus

Myofibril

Motor neuron

Blood capillary

Endomysium

Epimysium

a. Muscles are bundles of longitudinal muscle fibers (cells) surrounded by connective tissue. Each fiber has an artery, 1–2 veins, and a motor nerve cell.

Thecylindricalmusclefibers(cells)containmyofibrils,consistingofoverlappingthinfilamentsandthickfilamentsthatarearrangedintosarcomeres.Thisarrangementofoverlappingfilamentsallowsthemuscletoshorten,therebygeneratingforceandmovements.

S keletal muscles allow us to move. They can shorten (contract), thereby generating the force for movement. Muscles can also relax and return to their original length. The spe-

cific structure and arrangement of skeletal muscle al-lows its muscle cells to work the way they do. Let’s take a closer look.

Muscles are Composed of Bundles of Muscle FibersMuscles consist of bundles of muscle fibers or muscle cells wrapped in connective tissue (Figure 6.2). (Note that we use the terms muscle fibers and mus-cle cells interchangeably; they mean the same thing.) Each wrapped bundle of fibers is called a fascicle. The individual muscle cells are

fascicle �(FAS-i-kul) A small bundle or clus-ter of skeletal muscle fibers.

ThE PlAnnEr✓✓

Sarcolemma

Sarcoplasm

Sarcoplasmic reticulum

Myofibril

Nucleus

Thin filamentThick filament

SarcomereZ disc

Details of a muscle fiber

Mitochondrion

Triad:

Terminalcisterns

Transversetubule

Z disc Z disc

Thin filament

Thickfilament

Sarcomere

Thin filamentThick filament Z discZ disc

Sarcomere

Details of filaments and Z discs

H zone

A bandI band I band

Thick filament

Myosin tail

A thick filament and a myosin molecule

Myosin heads

Actin Troponin Tropomyosin

Portion of a thin filament

Myosin-binding site (covered by tropomyosin)

b. Each muscle fiber (cell) consists of a plasma membrane surrounding bundles of cylindrical myofibrils, which are enveloped by sarcoplasmic reticulum. The sarcolemma (plasma membrane) regularly invaginates at the transverse tubule. Fibers contain mitochondria and numerous nuclei.

c. Each myofibril consists of overlapping patterns of thick and thin filaments subdivided into regular compartments called sarcomeres. Sarcomeres have alternating dark bands (A-bands) and light bands (I-bands). At the center of each A-band is a lighter H-zone. In the middle of each I-band is a Z-disc or Z-line. A sarcomere stretches from Z-disc to Z-disc.

d. Thick filaments are made out of golf club-shaped proteins called myosin that are twisted together. Thin filaments are made of twisted strands of bead-like proteins called actin and are anchored to the Z-discs. The grooves of the actin strands are covered with a protein called tropomyosin. Each tropomyosin molecule has two troponin proteins on one end.


shorten. The proteins and the surrounding connective tis-sue are stretchable and allow muscle cells to lengthen. Let’s take a closer look at this arrangement of the myofilaments, which allows muscle cells to both contract and relax.

the Sliding Filament theory explains Muscle ContractionEarly on, scientists thought that muscle cells fold

when they contract, thereby causing mus-cles to shorten. However, when scientists in the 1950s examined relaxed and contracted muscle cells with electron microscopes, they found that the lengths of the thick and thin filaments do not change; only the length of the sarcomere changes. Physiologists A. L. Hodgkin and H. E. Huxley explained these

findings with a hypothesis called the sliding filament the-ory, in which thin filaments slide past the thick fila-ments (Figure 6.3).

cylindrical. Like other cells, muscle fibers have mitochon-dria to provide energy and a plasma membrane to sepa-rate the inside of the cell from the outside environment. However, skeletal muscle cells differ from other cells in several ways:

• A muscle cell has more than one nucleus.

• A muscle cell’s plasma membrane invaginates regu-larly into the deep parts of the muscle fiber to form a transverse tubule, or T-tubule.

• The endoplasmic reticulum of a muscle cell is called the sarcoplasmic �reticulum. The primary function of the sarcoplasmic reticulum is to serve as a reservoir to store calcium ions between muscle con-tractions. The regularly structured sarco-plasmic reticulum ends as small sacs near the T-tubules.

The arrangement of myofilaments (threadlike proteins) and other proteins within the muscle fibers allows them to

Sliding filament theory of muscle contraction • Figure 6.3

Whenmusclescontract,thinfilamentsslidealongthethickfilamentstowardtheM-line,therebyshorteningthesarcomere.WhenthethickfilamentsbuttupagainsttheZdiscs,thesarcomerecannotshortenanymore.

2 Sarcomeres

H zone I band

A band I band

A band

Z disc Thin filamentThick filament

Z disc M line Z disc

a. Relaxed muscle

b. Partially contracted muscle

c. Maximally contracted muscle

H zone

I band

Z disc Z discM line

sarcoplasmic �reticulum �(sar'-ko-PLAZ-mik re-TIK-u-lum) A network of saccules and tubes surround-ing myofibrils of a muscle fiber.

Muscles Are Built to Move 159

The contraction (cross-bridge) cycle • Figure 6.4

PR

oC

ESS D

iAg

RA

MThE PlAnnEr✓✓

any one instant, some of the myosin heads are attached to actin, forming cross-bridges, and generating force, and other myosin heads are detached from actin and getting ready to bind again. How is muscle contraction initiated? How is it stopped? This process, called exci-tation–contraction coupling, begins with a nerve impulse. Let’s take a closer look.

The myosin heads grab onto the binding sites of the actin filaments to form cross-bridges and then pull the actin filaments along in a repeating process called the cross-bridge cycle or contraction cycle (Fig-ure 6.4). This contraction cycle requires calcium ions (Ca2+) and ATP. The contraction cycle repeats as long as ATP and Ca2+ are available in the sarcoplasm. At

Myosin head picks up fresh ATP, drops actin, and resets to again form cross-bridges.

1

4

2

3

Calcium binds to thin filaments exposing actin active site.

The contraction cycle continues as long as ATP is available and Ca2+ levels in the cytoplasm are high.

ADP

ADPADP

ADP

ATP

PP

PADPP

=

Key:

ATP

ATP

Myosin heads react to actin active site, creating cross-bridges.

Myosin head bends toward H zone, pulling actin and Z disk inward.

ATP

ADP

Ca2+

Actin

Tropomyosin

Troponin

Myosin

Ca2+

Power stroke


Axon terminal

Axon terminal

Axon ofmotor neuron

Sarcolemma

Myofibril

ACh is released from synaptic vesicle

ACh binds to AChreceptor

Junctional fold

Synaptic vesiclecontainingacetylcholine(ACh)

Sarcolemma

Synaptic cleft(space)

Motor end plate

Synaptic cleft(space)

Neuromuscular junction

Enlarged view of the neuromuscular junction

Binding of acetylcholine to ACh receptors in the motor end plate

Synaptic end bulb

Synapticend bulb

Neuromuscularjunction (NMJ)

Synaptic end bulb

Motor end plate

Nerve impulse

Muscle action potential is produced

ACh is broken down

Na+

4

3

1

2

Impulse transmission at the neuromuscular junction • Figure 6.5

PR

oC

ESS

DiA

gR

AM ThE PlAnnEr✓✓

This impulse (muscle action potential) reverses the normal electrical state of the membrane (depolarization) and ini-tiates contraction along the length of the muscle fiber.

The muscle action potential passes along the cell membrane and down into the T-tubules (Figure 6.6). The action potential causes calcium ions to be released through calcium channels from their storage site inside the sarcoplasmic reticulum. The rise in calcium ion level in the sarcoplasm (cytoplasm) initiates the contraction cycle. The muscle continues to contract until enough cal-cium ions get pumped back inside the sarcoplasmic reticu-lum. Once the calcium levels in the cytoplasm return to normal, the muscle relaxes. This process of returning to the resting state is referred to as repolarization.

nerve Signals initiate the Contraction of Skeletal MuscleAs mentioned earlier, skeletal muscle contraction can be voluntary. If you want to pick up a pencil, your brain initi-ates that voluntary muscle contraction using a nerve im-

pulse. So how is the nerve impulse transmitted from the nerve cell to the muscle cell? At a specialized meeting place between the two cells called a neuromuscular junc-tion, the neuron sends a chemical message (acethylcholine [ACh]) that starts an electrical impulse in the muscle cell (Figure 6.5).

neuromuscular � �junction (noo-ro-MUS-ku-lar) A synapse (functional junction) between the axon terminals of a motor neuron and the sarco-lemma of a muscle fiber.


Excitation–contraction coupling in skeletal muscle • Figure 6.6

PR

oC

ESS D

iAg

RA

MThE PlAnnEr✓✓

ACh diffuses across synaptic cleft, binds to its receptors in the motor end plate, and triggers a muscle action potential (AP).

Synaptic vesiclefilled with ACh

ACh receptor Acetylcholinesterase in synaptic cleft destroys ACh so another muscle action potential does not arise unless more ACh is released from motor neuron. Ca2+

Muscle action potential

Nerveimpulse

SR

Contraction: power strokes use ATP; myosin heads bind to actin, swivel, and release; thin filaments are pulled toward center of sarcomere.

Troponin–tropomyosincomplex slides back into position where it blocks the myosin binding sites on actin.

Muscle relaxes.

Ca2+ active transport pumps

release channels in SR close and active transport pumps use ATP to restore low level of Ca2+ in sarcoplasm.

2+

2+

Ca2+ binds to troponin on the thin filament, exposing the binding sites for myosin.

Transverse tubule

Ca Ca

Muscle AP traveling along transverse tubule opens Ca2+ release channels in the sarcoplasmic reticulum (SR) membrane, which allows calcium ions to flood into the sarcoplasm.

Elevated Ca2+

1

3

4

6

8

9

7

2

5

Nerve impulse arrives at axon terminal of motor neuron and triggers release of acetylcholine (ACh).

=Key:

Ca2+

= Ca2+ active transport pumps

= Ca2+ release channels

P u t I t To g e t h e r1.Whatmakesthemusclecontractinstep6?2.Whatkindofcontractionisshowninstep6?(a)apartialcontraction(b)amaximumcontraction3. Whydoesthemusclerelaxinstep9?4.Whichnumberedstepsinthisfigurearepartofthecontractioncycle?


Sources that provide ATP in working muscle • Figure 6.7

Heat

ATP

Cellular respirationin mitochondria

Oxygen fromhemoglobin in bloodor from myoglobinin muscle fibers

Pyruvic acidfrom glycolysis

Fatty acids liberatedfrom adipose cells

ATP

Glycolysis

c. Aerobic respiration requires oxygen from the blood or a muscle protein called myoglobin. Pyruvic acid gets broken down into carbon dioxide and water. The energy released gets captured to make ATP and some gets lost as heat. Aerobic respiration can also use amino acids and fatty acids to make ATP. This process provides more ATP than the others and can last a long time (e.g., minutes to hours of muscle activity).

Creatine

ADPADP

ATPATP

Energy for musclecontraction

2 Pyruvic acid

Muscle glycogen

Creatine phosphate

P

2 Lactic acid Into blood

Fromblood

2 (net gain)

Amino acids from protein breakdown

Relaxedmuscle

Contractingmuscle

Glucose

b. Anaerobic respiration (glycolysis) breaks glucose from glycogen into pyruvic acid through a series of steps. The ATP is used in muscle contraction and the pyruvic acid gets converted to lactic acid. Lactic acid is what makes muscles sore. Glycolysis provides ATP for a further 30–60 seconds.

a. Creatine-phosphate transfers phosphate from ADP to make ATP. This process gets exhausted within 15 seconds, so it is good for quick bursts of muscle activity. Once at rest, the muscle makes ATP and regenerates creatine phosphate.

CO

H O

2

2


ing vigorous physical activity, the heart rate and breath-ing rate generally remain elevated for a period of time to move more oxygen into the tissue, which helps “repay” this oxygen debt. The excess oxygen delivered to the tis-sues converts lactic acid back to glucose and glycogen, remakes creatine phosphate, and replaces the oxygen lost from myoglobin during aerobic respiration. (Myoglobin is a muscle protein that stores oxygen within the muscle cell.) Oxygen is also used for the following processes:

• Increased body heat speeds up other reactions in the body that use ATP, so oxygen is used to replenish these stores.

• Oxygen feeds hard-working heart and breathing muscles, which use more ATP.

• Oxygen replenishes ATP used in tissue repair processes.

Muscle Contraction Comes in Many Forms: twitch, tetanus, isotonic, and isometricThere are two categories of muscle contraction: twitch and tetanus (contracture). A twitch is a single muscle con-traction in response to a single nerve impulse. It consists of three periods: the latent period, contraction period, and relaxation period. Each period is associated with the events of excitation–contraction coupling (Figure 6.8).

Muscle contraction requires lots of energy. The energy comes from ATP, but stores of ATP can be exhausted with-in seconds. The body must be able to make ATP quickly to

keep up with the energy demand of the working muscle. ATP can come from three sources: cre-atine phosphate, anaerobic res-piration or glycolysis, and aerobic respiration (Figure 6.7). Anaero-bic respiration is respiration that does not require oxygen; oxygen is required for aerobic respiration.

When muscles can no longer contract, they become fatigued.

Although muscle fatigue can come from a decrease in the release of calcium (calcium depletion), it most often results from insufficient supplies of ATP (due to depleted amounts of creatine phosphate and glycogen, inadequate delivery of oxygen to the muscle, or build-up of lactic acid). Sometimes, as ATP levels decrease and lactic acid levels increase, muscle cramping may also occur because muscles cells cannot relax. This is because the active transport process that moves calcium out of the cell also requires ATP.

After strenuous exercise, the oxygen consumption by working muscles continues to be elevated. This elevated oxygen consumption is referred to as oxygen debt. Follow-

Phases of a muscle twitch • Figure 6.8

glycolysis �(glı-KOL-i-sis) A series of anaero-bic chemical reactions in the cytosol of a cell in which a molecule of glucose is split into two molecules of pyruvic acid, with the net production of two ATPs.

Amyogramrecordsthepropertiesofatwitchinresponsetoasinglestimulus(arrow),startingwiththelatentperiod,movingtothecontrac-tionperiod,andthentotherelaxationperiod.Noticethatthetwitchlastsonlyabout50ms,or0.05s.

1. �Latent �period.Thereisatimedelayduringwhichthemuscleactionpotentialtravelsdownthemuscleandcalciumionsgetreleasedfromthesarcoplasmicreticulum.

2. �Contraction �period.Contractioncyclesgenerateforce.

3. �Relaxation �period.Ionizedcalciumlevelsinthecellreturntonormalandcontractioncyclesdecrease.

Time in milliseconds (msec)

0 10 20 30 40 50

1. Latent period

3. Relaxationperiod

For

ce o

f con

trac

tion

2. Contractionperiod


when you move your forearm toward your arm, the bi-ceps muscle shortens, moving the forearm. In contrast, isometric contraction results in a change of the ten-sion that is generated but does not cause motion. For ex-ample, when you stand, your back muscles must contract continually to maintain your upright posture.

Even when a whole muscle is not con-tracting, a small number of its motor units are involuntarily activated to produce a sus-tained contraction of their muscle fibers. This process, which results in muscle �tone,

occurs in both skeletal and smooth muscle. For example, the smooth muscles in your ar-teries and veins always have some degree of tone to maintain your blood pressure.

A twitch lasts only a short time and does not produce much tension. In contrast, tetanus is a longer, sustained contraction that develops more force than a twitch. There are two ways to increase the amount of tension and transi-tion from a twitch to tetanus (Figure 6.9):

• Temporal summation (or wave summation) increases the frequency of nerve impulses (that is, the number of impulses per second).

• Motor �unit recruitment increases the number of motor units stimulated at one time.

Most muscles use both methods to control and main-tain sustained contractions. Sustained contractions are also maintained by asynchronous (unsynchronized) stimu-lation of various motor units.

Muscle contraction can be isotonic or isometric. In iso-tonic contractions, muscle length changes. For example,

Mechanisms for controlling muscle twitch and tetanus • Figure 6.9

motor �unit �A motor neuron together with the muscle fibers it stimulates.

muscle �tone �A state of continued partial contraction.

Time (msec)

For

ce o

f con

trac

tion

a. Single twitch

Myograms

Actionpotential

b. Wave summation c. Unfused tetanus d. Fused tetanus

Muscle fibers (cells)

MotorneuronsSpinal cord

Neuromuscularjunction

Increase frequencyof nerve impulses

Increase the numberof motor units involved

Motor unit recruitment

Increased muscle tension(twitch to tetanus)

Effects of summation on contraction:a. Single twitchb. Wave summation — when subsequent stimuli arrive before the first wave is finished, the tension is higherc. Unfused tetanus — continued wave summations add together, but each stimulus has a partial relaxation (20-30 impulses/s)d. Fused tetanus — contraction force is steady and sustained (80-100 impulses/s)

As each subsequent stimulus arrives before the previous wave returns to normal, the levels of cytoplasmic Ca2+

accumulate and produce greater contractions up to a maximum when all motor units are recruited

Motor unit

Smooth Muscle Tissue is in the Walls of Most organs 165

need lots of this muscle fiber type, as these muscles allow rapid reactions and short bursts of speed.

Most skeletal muscles have all three types of fibers. About 50 percent of the fiber composition is SO fibers. Depend-ing on the muscle, the rest of the composition varies. For example, arm and shoulder muscles have high proportions of FG fibers, while leg muscles have large numbers of both SO and FOG fibers. Regardless of the overall mixture of muscle fibers within any given muscle, a single motor unit consists of identical fiber types. Therefore, there are SO motor units, FOG motor units, and FG motor units. These motor units are recruited in specific orders, depending on whether speed, force, or duration of contraction is re-quired in the muscle action.

1. Which skeletal muscle organelle stores and releases calcium?

2. What does ATP do in the contraction, or cross-bridge, cycle?

3. through what steps is the action potential stimulus translated into sliding filament contrac-tions?

4. Which type of muscle fibers would dominate the movements of your arm muscles in perform-ing short but powerful contractions, as in throw-ing a ball or swinging a tennis racket?

Based on the type of metabolism and the rate at which tension develops, skeletal muscle fibers can be classified into three types:

• Slow oxidative (SO) fibers have small diameters, contain many large mitochondria, and appear red because they contain large amounts of myoglobin. They make ATP mainly by aerobic respiration, develop tension relatively slowly, resist fatigue, and are capable of prolonged, sustained contractions. Such muscle fibers are found in large numbers in the muscles associated with posture. These are also the most important muscle fiber type for long-distance runners, who require endurance.

• Fast oxidative-glycolytic (FOG) fibers are inter-mediate in diameter. They have large amounts of myoglobin and therefore appear red. They make ATP through both aerobic respiration and glycolysis, so they are moderately resistant to fatigue. Most of the muscle fibers associated with large motor skills are of this type. They contract and relax faster than SO fibers but less quickly than the FG fiber type, providing an intermediate level of contraction sustainability. Middle-distance runners rely heavily on this type of muscle fiber.

• Fast glycolytic (FG) fibers are large and white, with considerable amounts of glycogen, but no myoglobin. Because they make ATP mainly through glycolysis, they fatigue rapidly. However, they contract and relax quickly, providing a short surge of power. Many of these fibers are found in areas where fine motor skills occur. Sprinters

Smooth Muscle tissue looks Very Different from Skeletal Muscle tissueSmooth muscle cells are much smaller than cells of other muscle types, and they are spindle-shaped. Smooth muscle differs from skeletal muscle in a number of ways:

• Each smooth muscle cell has a single nucleus and no striations because the thin and thick filaments are not arranged regularly.

• Because smooth muscle cells are small and thin, there are no transverse tubules.

• Each cell contains intermediate filaments and dense bodies, which are equivalent to the Z-discs in

Smooth Muscle Tissue Is in the Walls of Most OrganslearninG OBJeCtiVeS1. explain the structure of smooth muscle.2. Differentiate the classes of smooth muscle and

describe where they are found.

S mooth muscles are found in the walls of all hollow organs, such as blood vessels, the stom-ach, and the intestines. (They are also found in the skin, attached to hair follicles.) Because of

their unique structure, they are capable of being stretched much more than skeletal or cardiac muscle and can main-tain steady levels of contractions for long periods of time.


of both types have the structural features listed above, but the appearance of the contraction differs between the two. Visceral smooth muscle cells are interconnected by gap junctions and function as a group to produce a wave-like contraction known as peristalsis. Multi-unit smooth muscle does not contain gap junctions, so the cells func-tion independently, allowing more pinpoint control of the contraction.

Smooth muscles contract or relax involuntarily in response to stimulation by neurons of the autonomic (invol-untary) nervous system. Smooth muscles also respond to hormones and local events, such as changes in pH, carbon dioxide levels, temperature, and ion concentrations.

skeletal muscle. Some of the dense bodies are within the cytoplasm, and others are attached to the cell membrane. This arrangement gives the intermediate filament network a net-like appearance.

• Smooth muscle cells do not have a well-developed sarcoplasmic reticulum.

Smooth Muscle tissue Comes in two Varieties: Visceral and Multi-unitThere are two types of smooth muscle tissue: visceral (single-unit) muscle tissue and multi-unit smooth muscle tissue (Figure 6.10). The smooth muscle cells

Types and structure of smooth muscle cells • Figure 6.10

Whetherarrangedassingle-ormulti-unitsmoothmuscletissue,thestructureofindividualsmoothmusclecellsisthesame.

1. Why do smooth muscle cells lack striations? 2. Which type of smooth muscle tissue would you find in the walls of your stomach?

Sarcolemma

Intermediatefilament

Dense body

Nucleus

Thick filament

Thin filament

Relaxed Contracted

AutonomicneuronsNucleus

Musclefibers

Visceral (single-unit) smooth muscle tissue:• Most common• Found in sheets that form

walls of hollow organs• Tightly bound together• One neuron to many smooth

muscle cells• Smooth muscle cells

communicate via gap junctions• Many cells contract in unison• Found in small arteries, veins,

stomach, intestines, uterus, bladder

Multi-unit smooth muscle tissue:• Loosely bound together• One neuron to one

smooth muscle cell• Individual cells contract

independently• Found in blood vessels,

airways, arrector pili of hairs, and internal eye muscles


Cardiac Muscle Tissue Forms the Muscular Wall of the heart

learninG OBJeCtiVeS1. Describe the structure of cardiac

muscle tissue.2. Compare cardiac muscle, skeletal

muscle, and smooth muscle.

T he heart is composed mostly of car-diac muscle tissue. This tissue has some of the characteristics seen in skeletal muscle and some of those

seen in smooth muscle tissue, creating a unique type of muscular tissue.

Cardiac muscle has a structure that is intermediate between skeletal muscle and smooth muscle (Figure 6.11). Cardiac cells are larger than smooth muscle cells but smaller than skeletal muscle cells. Like skeletal muscle, they have cylindrical myofibrils, sarcomeres, T-tubules, and a fairly well-developed sarcoplasmic reticulum. Like single-unit smooth muscle cells, cardiac cells commu-nicate with one another through gap junctions in the

intercalated � discs between them. Cardiac cells are unique in that they are often branched.

Cardiac cells respond to signals from special-ized heart muscle cells called pacemaker cells, which in turn are influenced by the autonomic nervous system. Pacemaker cells are autorhythmic; they can contract on their own, without nervous sys-tem stimulation. Via pacemaker cells, the auto-nomic nervous system can speed up or slow down the contraction of cardiac cells as needed. Unlike other types of muscle cells, cardiac cells can pro-duce only twitch contractions, and they do so at a rate of 70 to 80 contractions per minute. The actions of cardiac muscle are discussed more fully in Chapter 11.

1. What is the function of intercalated discs?2. What is the source of action potentials in car-

diac muscle? in skeletal muscle?

Structure of cardiac muscle cells • Figure 6.11

intercalated �disc � �(in-TER-ka-lat-ed) An irregular trans-verse thickening of sarcolemma where two cardiac cells come together. The intercalated disc is composed of desmo-somes, which hold cardiac muscle fibers together, and gap junctions, which aid in conduction of muscle action potentials from one fiber to the next.

Cardiac muscle cells have numerous, largemitochondria.

Cardiac muscle cells areoften branched.

Cardiac muscle cells have one large nucleus.

Sarcolemma (plasma membrane)

Intercalated discs are thickenings of plasma membrane where two cardiac muscle cells come together. They hold cells together and aid in cell–cell communications.

Opening of T-tubule

Cardiac muscle cells are smaller than skeletal muscle fibers, but larger than smooth ones.


Skeletal Muscles Are Grouped Based on location and Action

learninG OBJeCtiVeS1. explain how skeletal muscles make bones

move.2. identify major muscle groups of the upper body.3. Describe major muscle groups of the lower

body.

T he body consists of around 700 skeletal mus-cles that are grouped based on their locations and actions. Muscles of the upper body con-trol functions of the head and neck, shoulder,

and arms, thorax, and abdomen. Muscles of the lower body move the legs and pelvis.

Skeletal Muscles Work in GroupsSkeletal muscles attach to bones via bands of connective tissue called tendons. Two bones are usually involved in the movement of a joint: one is stationary, and the other one moves. The location where a muscle attaches to a station-ary bone via a tendon is called the origin. The other end of the muscle is attached by means of a tendon to the mov-able bone at a point called the insertion. The fleshy por-tion of the muscle, between the tendons of the origin and insertion, is called the belly (Figure 6.12).

A good analogy is a spring on a door. The part of the spring attached to the door represents the insertion, the part attached to the frame is the origin, and the coils of the spring are the belly.

relationships of muscles to bones • Figure 6.12

Shoulder joint

Scapula

ORIGIN of triceps brachiifrom scapula and humerus

BELLYof tricepsbrachiimuscle

Tendon

INSERTION of triceps brachii on ulna

Elbow joint

Ulna

ORIGIN of biceps brachiifrom scapula

BELLYof bicepsbrachiimuscle

Tendon

INSERTION of biceps brachii on radius

Radius

Tendons

STATIONARY BONE – For movement of the arm, this is the humerus.

MOVABLE BONES – For movement of the forearm, the ulna and radius are movable bones. Each has a different muscle attached.

Theendsofmuscleshavedifferentnames,dependingonwheretheyareattached.Theyworkingroupsorpairsthathaveopposingactions.Formovementsoftheelbow,thebicepsandtricepsareamusclepairwithopposingactions.

Skeletal Muscles Are grouped Based on Location and Action 169

WHAT A HEALTH PRoviDER SEESThE PlAnnEr✓

ments. Some muscles in a group act as fixators, stabilizing one of the bones so the agonist can move the other bone more efficiently. During arm movement, for example, muscles associated with the scapula serve as fixators to stabilize the scapula while the humerus moves. Depending on the movement and the conditions, many muscles can switch roles, acting as agonists, antagonists, synergists, or fixators at different times. Exercise is important to main-taining healthy muscles (see What a Health Provider Sees).

As mentioned earlier, there are about 700 skeletal muscles, each with a different name. For an overview of selected superficial muscles of the human body, (Figure 6.13 on the following pages.)

Muscles work in groups, usual-ly as pairs of muscles with opposing actions. The muscle that starts the desired action is the prime �mover, or agonist. As the agonist contracts, the muscle with an opposing action, called the antagonist, relaxes. For

example, when you flex (bend) your arm at the elbow, the biceps is the agonist and the triceps is the antagonist. When you extend your arm, the two muscles switch roles.

Most movements involve additional muscles called synergists (SIN-er-gists). A synergist helps the agonist function more efficiently by reducing unnecessary move-

prime �mover � �The muscle directly responsible for producing a desired motion. Also called the agonist.

1. Softtissueinjuries(sprainsormusclepulls)arecommoninathletes.Thesofttissuesgenerallyinvolvedintheseinjuriesaretheligamentsandtendons.Musclestrains(aches)canalsooccurifmusclesarestretchedtoomuch.Oneimportantpartofthetreatmentforsuchinjuriesis

rest.Whywouldrestbeanintegralpartofthetherapyforhealingsofttissueandmuscleinjuries?2. Samjuststartedanexerciseregime.Atfirst,hewasstiff,andhismusclesfatiguedeasily.Afterseveralweeksofexer-cising,however,Samnoticesthatheismoreflexibleandcantoleratelongerandlongersessions.Whatishappeninghere?

T h i n k C r i t i c a l l y

a. �

b. �

Exercise Maintains healthy Muscles

Stretchingpriortoexerciseisasimportantasexerciseinmaintainingyourmusclehealth.Properstretching

(Figure a)lengthenstheconnectivetissueassociatedwiththemusclesandimprovesflexibility.Stretchingshouldnotonlybedonepriortoexercisebutalsoonaregular,dailybasis.Frequentstretchingcanreducemuscleten-sion,improveagility,andincreaserangeofjointmotion.Stretchingshouldbedoneslowly,withtheapplicationofgentleforcetopreventinjurytothemuscleorassociatedconnectivetissues.

Exercisedoesnotchangethetotalnumberofmusclefibersbutcanaffectthedistributionofmusclefibertypeswithinworkingmuscles.AlthoughyourratioofFGfiberstoSOfibersisdeterminedbygenetics,youcanchangetheproportionofFOGfiberswithexercise.Forexample,aerobic/enduranceexercisessuchasrunning(Figure b)orswimmingcancausesomeFGfiberstochangeintoFOGfibers.ThenewFOGfibersarelargerandhaveincreasednumbersofmitochondria,increasedbloodsupply,andstrength.Theincreasedsize(hypertrophy)iscausedbyincreasedsynthesisofadditionalmyosin,actin,troponin,andtropomyosin.

Incontrast,lackofexercisecausesalossofmusclemass.Thisisespeciallytrueinbedriddenpatientsandastronautsinmicrogravity(seetheopeningtoChapter5).Themusclefibersdecreaseinsize(atrophy)asthemuscleproteinsdegrade. Video


Orbicularis oris

Platysma

Orbicularis oculi

Masseter

Sternocleidomastoid

Trapezius

Deltoid

Pectoralis majorSerratus anterior

Biceps brachii

Brachialis

Triceps brachii

Brachioradialis

Flexor carpi radialis

Tibialis anterior

Fibularis longus

External oblique

Rectus abdominis

Brachioradialis

Tensor fasciae latae

Psoas major

Sartorius

Adductor magnus

Gracilis

Vastus lateralis

Rectus femoris

Vastus medialis

Gastrocnemius

Soleus

a. Anterior view

Occipitofrontalis (frontal belly) Temporalis

Latissimus dorsi

Temporalis

External oblique

Gluteus medius

Gluteus maximus

Gracilis

Vastus lateralis

Adductor magnusSemitendinosus

Semimembranosus

Sartorius

SoleusSoleus

Fibularis longus

Biceps femorisIliotibial tract

Tensor fasciaelatae

Sternocleidomastoid

Trapezius

Deltoid

Extensor digitorum

Extensor carpi ulnaris

Flexor carpi ulnaris

Gastrocnemius

b. Posterior view

Triceps brachii

Occipitofrontalis (occipital belly)

Brachioradialis

The principal skeletal muscles of the human body • Figure 6.13


Orbicularis oris

Platysma

Orbicularis oculi

Masseter

Sternocleidomastoid

Trapezius

Deltoid

Pectoralis majorSerratus anterior

Biceps brachii

Brachialis

Triceps brachii

Brachioradialis

Flexor carpi radialis

Tibialis anterior

Fibularis longus

External oblique

Rectus abdominis

Brachioradialis

Tensor fasciae latae

Psoas major

Sartorius

Adductor magnus

Gracilis

Vastus lateralis

Rectus femoris

Vastus medialis

Gastrocnemius

Soleus

a. Anterior view

Occipitofrontalis (frontal belly) Temporalis

Latissimus dorsi

Temporalis

External oblique

Gluteus medius

Gluteus maximus

Gracilis

Vastus lateralis

Adductor magnusSemitendinosus

Semimembranosus

Sartorius

SoleusSoleus

Fibularis longus

Biceps femorisIliotibial tract

Tensor fasciaelatae

Sternocleidomastoid

Trapezius

Deltoid

Extensor digitorum



Gastrocnemius

b. Posterior view

Triceps brachii

Occipitofrontalis (occipital belly)

Brachioradialis


shape, action, number of origins, and location (see Table 6.1).

The names of the skeletal muscles often relate to muscle characteristics such as fiber direction, size,

Characteristics used to name skeletal muscles Table 6.1

Name Meaning Example

Direction: Orientation of muscle fibers relative to the body’s midline

RectusTransverseOblique

ParalleltomidlinePerpendiculartomidlineDiagonaltomidline

RectusabdominisTransverseabdominisExternaloblique

Size: Relative size of the muscle

MaximusMinimusLongusLatissimusLongissimusMagnusMajorMinorVastus

LargestSmallestLongestWidestLongestLargeLargerSmallerGreat

GluteusmaximusGluteusminimusAdductorlongusLatissimusdorsiLongissimusmusclesAdductormagnusPectorallismajorPectorallisminorVastuslateralis

Shape:Relative shape of the muscle

DeltoidTrapeziusSerratusRhomboidOrbicularisPectinatePiriformisPlatysQuadratusGracilis

TriangularTrapezoidSaw-toothedDiamond-shapedCircularComblikePear-shapedFlatSquareSlender

DeltoidTrapeziusSerratusanteriorRhomboidmajorOrbicularisoculiPectineusPiriformisPlatysmaQuadratuslumborumGracilis

Action:Principal action of the muscle

FlexorExtensorAbductorLevatorDepressorSupinatorPronatorSphincterTensor

DecreasesjointangleIncreasesjointangleMovesboneawayfrommidlineProducessuperiormovementProducesinferiormovementTurnspalmanteriorlyTurnspalmposteriorlyDecreasessizeofopeningMakesabodypartrigid

FlexorcarpiradialisExtensorcarpiulnarisAdductorlongusLevatorscapulaeDepressorlabiiinferiorisSupinatorPronatorteresExternalanalsphincterTensorfasciaelatae

Number of Origins:Numberoftendonsoforigin

BicepsTricepsQuadriceps

TwooriginsThreeoriginsFourorigins

BicepsbrachiiTricepsbrachiiQuadricepsfemoris

Location: Structure near which a muscle is found Example: Temporalis, a muscle near the temporal bone.

Origin and Insertion: Sites where muscle originates and inserts Example: Brachioradialls, originating on the humerus and inserting on the radius (brachii =arm).


riety of emotions, such as happiness, displeasure, fear, and surprise. Muscles that move the mandible (lower jaw) are involved in biting and chewing. Because of this, they are also known as muscles of mastication (chewing). These muscles also help in speech. The muscles that control facial expression, speech, and chewing are il-lustrated in Figure 6.14.

Muscles of the head and neck Control Facial expressions, allow You to Speak and Chew, and enable Your eyes to Open, Close, and MoveMuscles of the head and neck produce facial expres-sions that give humans the ability to express a wide va-

Muscles of the head and neck • Figure 6.14

Muscle Origin Insertion Action

Muscles of the head and neck that produce facial expressions

Occipitofrontalis(ok-sip-i-to-frun-TA-lis)—dividedintofrontalbellyandoccipitalbelly Frontal belly Epicranialaponeurosis

(flattendonattachingfrontalisandoccipitalis)

Skinsuperiortoorbit Drawsscalpforward,asinfrowning;raiseseyebrows;andwrinklesskinofforeheadhorizontally,asinalookofsurprise

Occipital belly Occipitalandtemporal Epicranialaponeurosis Drawsscalpbackward

Orbicularis oris (or-bi’-ku-LAR-isOR-is)

Musclefiberssurroundingtheopeningofthemouth

Skinatthecornerofthemouth Closesandprotrudeslips,asinkissing;compresseslipsagainstteeth;andshapeslipsduringspeech

Zygomaticus major (z ı-go-MA-ti-kus)

Zygomaticbone Skinattheangleofthemouthandorbicularisoris

Drawsangleofmouthupwardandoutward,asinsmilingorlaughing

Buccinator (BUK-si-na’-tor)

Maxillaandmandible Orbicularisoris Pressescheeksagainstteethandlips,asinwhistling,blowing,andsucking;drawscornerofmouthlaterally;assistsinchewingbykeepingfoodbetweenteeth

Platysma(pla-TIZ-ma)

Fasciaoverdeltoidandpectoralismajor

Mandible,musclesaroundangleofmouth,skinoflowerface

Drawsouterpartoflowerlipdownwardandbackward,asinpouting;depressesmandible

Orbicularis oculi (OK-u-lı)

Medialwalloforbit Circularpatharoundorbit Closeseye

Muscles of the head and neck that control speech and chewing

Masseter (MA-se-ter) Maxillaandzygomaticarch

Mandible Elevatesmandible,asinclosingmouth

Temporalis (tem’-por-A-lis) Temporalbone Mandible Elevatesandretractsmandible

Right lateral superficial view

Occipitofrontalis(frontal belly)

Orbicularis oculi

Buccinator

Orbicularis oris

Platysma

Temporalis

Occipitofrontalis(occipital belly)

Mandible

Masseter

Zygomaticus major


These muscles are among the fastest contracting and most precisely controlled skeletal muscles in the body. These muscles are illustrated in Figure 6.15, which also provides their respective origins, insertions, and actions.

The muscles that move the eyeballs are extrinsic muscles because they originate outside the eyeball and are inserted on the outer surface (ex- = out of). They move the eyeballs in various directions.

Muscles of the head that move the eyeballs and upper eyelids • Figure 6.15

Superior oblique

Levator palpebraesuperioris (cut)

Superior rectus

Inferior rectus

Inferior oblique

Lateral rectus

Medial rectus

Lateral view of right eyeball


Muscles of the head that move the eyeballs and upper eyelids

Superior rectus (REK-tus)

Tendinousringattachedtobonyorbitaroundopticforamen

Superiorandcentralpartofeyeball

Moveseyeballupward(elevation)andmedially(adduction)androtatesitmedially

Lateral rectus Sameasabove Lateralsideofeyeball Moveseyeballlaterally(abduction)

Medial rectus Sameasabove Medialsideofeyeball Moveseyeballmedially(adduction)

Superior oblique (o-BLEK)

Sameasabove Eyeballbetweensuperiorandlateralrecti;themusclemovesthrougharingoffibrocartilaginoustissuecalledthetrochlea

Moveseyeballdownward(depression)andlaterally(abduction)androtatesitmedially

Inferior oblique Maxilla Eyeballbetweeninferiorandlateralrecti

Moveseyeballupward(elevation)andlaterally(abduction)androtatesitlaterally

Levator palpebrae superioris (le-VA-torPAL-pe-bresoo-per’-e-OR-is)

Roofoforbit Skinofuppereyelid Elevatesuppereyelid(openseye)


ing inhalation (breathing in), the cavity increases in size; during exhalation (breathing out), the cavity decreases in size. Muscles that help move the shoulder also act to hold the scapula in place so that it is a stable point of ori-gin for the muscles that move the humerus. These mus-cles are illustrated in Figure 6.16, which also provides their respective origins, insertions, and actions.

Muscles of the thorax, abdomen, neck, and Back perform Many FunctionsMuscles of the thorax (chest) have three functions: They are involved in breathing, movement of the shoulder, and movement of the humerus. The chest muscles involved in breathing alter the size of the thoracic cavity. Dur-

Muscles of the thorax involved in breathing • Figure 6.16


Muscles of the thorax involved in breathing

Diaphragm(DI-a-fram) Xiphoidprocessofsternum,costalcartilagesofinferiorsixribs,lumbarvertebrae,andtheirintervertebraldiscs

Centraltendon(strongaponeurosisnearthecenterofthediaphragm)

Contractioncausesittoflattenandincreasesthevertical(top-to-bottom)dimensionofthethoraciccavity,resultingininhalation;relaxationcausesittomovesuperiorlyanddecreasestheverticaldimensionofthethoraciccavity,resultinginexhalation

External intercostals Inferiorborderofribabove

Superiorborderofribbelow Contractionelevatestheribsandincreasestheanteroposteriorandlateraldimensionsofthethoraciccavity,resultingininhalation;relaxationdepressestheribsanddecreasestheanteroposteriorandlateraldimensionsofthethoraciccavity,resultinginexhalation

Internal intercostals Superiorborderofribbelow

Inferiorborderofribabove Contractiondrawsadjacentribstogethertofurtherdecreasetheanteroposterior(front-to-back)andlateral(side-to-side)dimensionsofthethoraciccavityduringforcedexhalation

Internalintercostals

Externalintercostals

Externalintercostals

Rib

Sternum

Diaphragm

Anterior superficial view Anterior deep view

Internalintercostals


or scapula. Figure 6.17 illustrates and describes these muscles.

Muscles of the thorax that move the shoulder orig-inate on the axial skeleton and insert on the clavicle

Muscles of the thorax that move the shoulder • Figure 6.17

Clavicle

Levator scapulaeLevator scapulae

Trapezius

Pectoralisminor

Humerus

Serratusanterior

Externalintercostal

Internalintercostal

Serratusanterior

Anterior deep view Anterior deeper view

Ribs

Scapula

10 10

9 9

8 8

7 7

7

6

5

4

6 6

5

4

3

2

1

3

2

1


Muscles of the thorax that move the shoulder

Pectoralis minor(pek’-tor-A-lis;pect-=breast,chest,thorax;minor=lesser)

Secondthroughfifth,thirdthroughfifth,orsecondthroughfourthribs

Scapula Abductsscapulaandrotatesitdownward(movementofglenoidcavityupward);elevatesthirdthroughfifthribsduringforcedinhalationwhenscapulaisfixed

Serratus anterior(ser-A-tus;serratus=saw-toothed;anterior=front)

Uppereightornineribs Scapula Abductsscapulaandrotatesitupward(movementofglenoidcavitydownward);elevatesribswhenscapulaisfixed;knownas“boxer’smuscle”becauseitisimportantinhorizontalarmmovementssuchaspunchingandpushing

Trapezius(tra-PE-ze-us;trapeze-=trapezoid-shaped)

Occipitalboneandspinesofseventhcervicalandallthoracicvertebrae

Clavicleandscapula

Superiorfiberselevatescapula;middlefibersadductscapula;inferiorfibersdepressandupwardrotatescapula;superiorandinferiorfiberstogetherrotatescapulaupward;stabilizesscapula

Levator scapulae(le-VA-torSKA-pu-le;levator=toraise;scapulae=ofthescapula)

Upperfourcervicalvertebrae

Scapula Elevatesandadductsscapulaandrotatesitdownward


Muscles of the abdomen that protect the abdominal organs • Figure 6.18

Four pair of muscles of the abdomen protect the abdominal organs. They include the rectus abdominis,

external oblique, internal oblique, and transverse abdomi-nis. Figure 6.18 illustrates and describes these muscles.


Muscles of the abdomen that protect the abdominal organs

Rectus abdominis (REK-tusab-DOM-in-is)

Pubisandpubicsymphysis

Cartilageoffifthtoseventhribsandxiphoidprocessofsternum

Flexesvertebralcolumnandcompressesabdomentoaidindefecation,urination,forcedexhalation,andchildbirth

External oblique Lowereightribs Crestofiliumandlineaalba(atoughconnectivetissuebandthatrunsfromxiphoidprocesstopubicsymphysis)

Contractionofbothexternalobliquescompressesabdomenandflexesvertebralcolumn;contractionofonesidealonebendsvertebralcolumnlaterallyandrotatesit

Internal oblique Ilium,inguinalligament,andthoracolumbarfascia

Cartilageoflastthreeorfourribsandlineaalba

Contractionofbothinternalobliquescompressesabdomenandflexesvertebralcolumn;contractionofonesidealonebendsvertebralcolumnlaterallyandrotatesit

Transverse abdominis Ilium,inguinalligament,lumbarfascia,andcartilagesoflastsixribs

Xiphoidprocess,lineaalba,andpubis

Compressesabdomen

External oblique (cut)

Rectus abdominis

Transverse abdominis

Internal oblique

Anterior superficial view Anterior deep view

External oblique

Rectus abdominis


1211

10

9

8

7

6

5

4

3

2

1

Deep view

Spinalis group(medial)

Longissimus group (intermediate)

Iliocostalis group (lateral)

the iliocostalis group, longissimus group, and spinalis group. These groups are illustrated in Figure 6.19. See Figure 6.13b for an illustration of the sternocleidomastoid, and see Figure 6.23 for illustrations of the quadratus lum-borum and psoas major.

Muscles of the neck and back are responsible for movement of the spine. These include the erector spinae, sternocleidomastoid, quadratus lumborum, and psoas ma-jor. The erector spinae is the largest muscular mass of the back and consists of three groups of overlapping muscles:

Muscles of the neck and back that move the spine • Figure 6.19


Muscles of the neck and back that move the spine

Erector spinae(e-REK-torSPI-ne;iliocostalisgroup,longissimusgroup,andspinalisgroup)

Allribspluscervical,thoracic,andlumbarvertebrae

Occipitalbone,temporalbone,ribs,andvertebrae

Extendshead;extendsandlaterallyflexesvertebralcolumn

Sternocleidomastoid (ster’-no-klı-do-MAS-toid)(seeFigure6.13b)

Sternumandclavicle Temporalbone Contractionsofbothmusclesflexcervicalpartofvertebralcolumnandflexhead;contractionofonemusclerotatesheadtowardsideoppositecontractingmuscle

Quadratus lumborum(kwod-RA-tuslum-BOR-um)(seeFigure6.23)

Ilium Twelfthribandupperfourlumbarvertebrae

Contractionsofbothmusclesextendlumbarpartofvertebralcolumn;contractionofonemuscleflexeslumbarpartofvertebralcolumn

Psoas major (SO-as)(seeFigure6.23)

Lumbarvertebrae Femur Flexesvertebralcolumn;flexesandrotatesthighlaterallyathipjoint

Second Pages

Deltoid (cut)

Supraspinatus

Teres major

Subscapularis

Pectoralismajor (cut)

Biceps brachii (cut)

Anterior deep view

Clavicle

Pectoralismajor (cut)

Pectoralis minor

Latissimus dorsi

123

4

5

6

7

DeltoidInfraspinatus

Supraspinatus(cut)

Scapula

Coraco-brachialis

Teres major

Teres minor

Teres major

Humerus Triceps brachii

Posterior view

Muscles of the shoulder and upper limb • Figure 6.20

forearm are also referred to as the pectoral girdle or shoul-der girdle. The muscles of the shoulder include the deltoid, subscapularis, supraspinatus, infraspinatus, teres major, and teres minor. Figure 6.20 illustrates and describes these muscles.

Muscles of the Shoulder and upper limb are Concerned with MovementYou learned in Chapter 5 that the pectoral girdle consists of the clavicle and scapula. The region of the muscles that attach to these bones and to the bones of the arm and


Muscles of the shoulder

Deltoid(DEL-toyd) Clavicleandscapula Humerus Abducts,flexes,extends,androtatesarmatshoulderjoint

Subscapularis (sub-scap’-u-LA-ris)

Scapula Humerus Rotatesarmmediallyatshoulderjoint

Supraspinatus(soo’-pra-spi-NA-tus)

Scapula Humerus Assistsdeltoidmuscleinabductingarmatshoulderjoint

Infraspinatus(in’-fra-spi-NA-tus)

Scapula Humerus Rotatesarmlaterallyatshoulderjoint

Teres major(TE-rez) Scapula Humerus Extendsarmatshoulderjoint;assistsinadductionandrotationofarmmediallyatshoulderjoint

Teres minor Scapula Humerus Rotatesarmlaterallyandextendsarmatshoulderjoint


The muscles of the arm have three functions: flex-ing the forearm, extending the forearm, and rotating the forearm. The biceps brachii, brachialis, and brachioradialis flex the forearm. The triceps brachii extends the forearm. The muscles responsible for the rotation of the forearm are the supinator and the pronator teres. Figure 6.21 illustrates and describes these muscles.

The two functions of the muscles of the forearm are moving the wrist and moving the hand and fingers. The

flexor carpi radialis, flexor carpi ulnaris, extensor carpi radialis longus, and extensor carpi ulnaris are all involved in the wrist motion required to toss a Frisbee. The muscles that let you grasp an object with your hand or move your fingers to play the piano include the palmaris longus, flex-or digitorum superficialis, flexor digitorum profundus, and extensor digitorum. Figure 6.22 illustrates all of these muscles and includes descriptions of their origins, inser-tions, and actions.


Muscles of the arm

Biceps brachii (BI-cepsBRA-ke-ı)

Scapula Radius Flexesandsupinatesforearmatelbowjoint;flexesarmatshoulderjoint

Brachialis(bra’-ke-A-lis) Humerus Ulna Flexesforearmatelbowjoint

Brachioradialis (bra’-ke-o-ra’-de-A-lis)

Humerus Radius Flexesforearmatelbowjoint

Triceps brachii (TRI-cepsBRA-ke-ı)

Scapulaandhumerus Ulna Extendsforearmatelbowjoint;extendsarmatshoulderjoint

Supinator(SOO-pi-na-tor) Humerusandulna Radius Supinatesforearm

Pronator teres (PRO-na-torTE-rez)

Humerusandulna Radius Pronatesforearm

Muscles of the arm that move the radius and ulna • Figure 6.21

Anterior view

Humerus

Deltoid (cut)

Biceps brachii:Long headShort head

Brachialis

Radius

Ulna

9

8

7

6

5

4

3

2

1

Teres major

Long head

Lateral head

Medial head

Triceps brachii:

Posterior view

Scapula

123

4

5

6

7

8

9

10

11

12

Humerus

UlnaRadius



Muscles of the forearm

Flexor carpi radialis (FLEK-sorKAR-pera’-de-A-lis)

Humerus Secondandthirdmetacarpals Flexesandabductshandatwristjoint

Flexor carpi ulnaris (ul-NAR-is)

Humerusandulna Pisiform,hamate,andfifthmetacarpal

Flexesandadductshandatwristjoint

Extensor carpi radialis longus (eks-TEN-sor)

Humerus Secondmetacarpal Extendsandabductshandatwristjoint

Extensor carpi ulnaris Humerusandulna Fifthmetacarpal Extendsandadductshandatwristjoint

Muscles of the forearm that move the wrist, hand, and fingers • Figure 6.22

HumerusBrachioradialisExtensor carpi radialislongus


Extensor digitorum


Ulna

Triceps brachii

Posterior view

Biceps brachiiBrachialis

Pronator teresBrachioradialisPalmaris longusFlexor carpi radialis


Flexor digitorumsuperficialis

Anterior superficial view


Gluteusmaximus (cut)

Gluteus maximus (cut)

Posterior deep view

Gluteusmedius (cut)

Piriformis

Adductor magnus

Vastus lateralis

Gastrocnemius

Posterior superficial view

Gluteus medius

Gluteus maximus

Tensor fasciaelatae

Gracilis

Semitendinosus

Sartorius

SemimembranosusBiceps femoris

Hamstrings:


Quadratus lumborum

Iliacus

Tensor fasciae lataeSartorius

Rectus femoris (cut)Quadriceps femoris:

Vastus lateralis

Vastus medialis

Vastus intermedius

Pectineus

Psoas major

Adductor longus

GracilisAdductor magnus

vide stability, locomotion, and maintenance of posture. Figure 6.23 lists their origins, insertions, and actions. Gluteal muscles move the thigh and include the gluteus maximus, gluteus medius, and piriformis. Thigh muscles can be divided into five groups, based on their functions:

Muscles of the lower Body Move the thigh and legsThe muscles of the lower body include those of the glu-teal region, thigh, and leg. These muscles are larger and more powerful than those of the upper limbs. They pro-

Muscles of the gluteal region that move the thigh • Figure 6.23

3. The hamstring group flexes the leg and includes the biceps femoris, semitendinosus, and semimembranosus.

4. The sartorius helps you cross your legs by weakly flexing the leg and the knee joint and flexing, abducting, and laterally rotating the thigh at the hip joint.

5. The tensor fasciae latae moves the thigh laterally.

1. The adductor group moves the thigh medially and includes the adductor magnus, adductor longus, pectineus, and gracilis.

2. The quadriceps group extends the leg and includes the vastus lateralis, vastus medialis, vastus intermedius, and rectus femoris.


Muscles of the gluteal region

Gluteus maximus (GLOO-te-usMAK-si-mus)

Ilium,sacrum,coccyx,andaponeurosisofsacrospinalis

Iliotibialtractoffascialataandfemur

Extendsandrotatesthighlaterallyatthehipjoint;helpslockkneeinextension

Gluteus medius (ME-de-us)

Ilium Femur Abductsandrotatesthighmediallyatthehipjoint

Piriformis(pir-i-FOR-mis) Sacrum Femur Rotatesthighlaterallyandabductsitatthehipjoint

Muscles of the thigh

Adductor group

Adductor magnus (MAG-nus)

Pubisandischium Femur Adducts,rotates,flexes,andextendsthighathipjoint

Adductor longus (LONG-us)

Pubisandpubicsymphysis

Femur Adducts,rotates,andflexesthighathipjoint

Pectineus(pek-TIN-e-us) Pubis Femur Flexesandadductsthighathipjoint

Gracilis(gras-I-lis)

Pubis Tibia Adductsandmediallyrotatesthighathipjoint,flexeslegatkneejoint

Quadriceps group

Vastus lateralis (VAS-tuslat’-er-A-lis)

Femur Patellabymeansofquadricepstendonandthentibialtuberositybymeansofpatellarligament

Extendlegatkneejoint

Vastus medialis (me-de-A-lis)



Vastus intermedius (in’-ter-ME-de-us)



Rectus femoris (REK-tusFEM-or-is)

Ilium Patellabymeansofquadricepstendonandthentibialtuberositybymeansofpatellarligament

Extendlegatkneejoint;flexthighathipjoint

Hamstrings

Biceps femoris (BI-cepsFEM-or-is)

Ischiumandfemur Fibulaandtibia Flexeslegatkneejoint;extendsthighathipjoint

Semitendinosus (sem’-e-TEN-di-no’-sus)

Ischium Tibia Flexeslegatkneejoint;extendsthighathipjoint

Semimembranosus (sem’-e-MEM-bra-no’-sus)

Ischium Tibia Flexeslegatkneejoint;extendsthighathipjoint

Sartorius(sar-TOR-e-yus)

Ilium Tibia Weaklyflexeslegatkneejoint;flexes,abducts,andlaterallyrotatesthighathipjoint,thuscrossingleg

Tensor fasciae latae (TEN-sorFA-she-eLA-te)

Ilium Tibiabymeansofiliotibialtract Flexesandabductsthighathipjoint;helpslockkneeinextension


The leg muscles can be divided into two groups: those that move the feet and those that allow you to wiggle your toes. The tibialis anterior, fibularis longus, gastrocnemius, so-leus, and tibialis posterior move the ankle. The extensor digitorum longus and flexor digitorum longus allow move-ment of the toes. See Figure 6.24 for an illustration of these muscles and details about their origins, insertions, and actions.

1. During movement, what is the role of the agonist?2. Which muscle groups are responsible for

breathing?3. Where would you find the gastrocnemius muscle?

Muscles of the leg that move the feet and toes • Figure 6.24


Muscles of the leg that move the feet

Tibialis anterior (tib’-e-A-lis)

Tibia Firstmetatarsalandfirstcuneiform Dorsiflexesandinverts(supinates)foot

Fibularis longus (fib-u-LAR-isLON-gus)

Fibulaandtibia Firstmetatarsalandfirstcuneiform Plantarflexesandeverts(pronates)foot

Gastrocnemius (gas’-trok-NE-me-us)

Femur Calcaneusbymeansofcalcaneal(Achilles)tendon

Plantarflexesfoot;flexeslegatkneejoint

Soleus(SO-le-us) Fibulaandtibia Calcaneusbymeansofcalcaneal(Achilles)tendon

Plantarflexesfoot

Tibialis posterior (tib’-e-A-lis)

Tibiaandfibula Second,third,andfourthmetatarsals;navicular;allthreecuneiforms;andcuboid

Plantarflexesandinvertsfoot

Muscles of the leg that move the toes

Extensor digitorum longus (eks-TEN-sordi’-ji-TOR-umLON-gus)

Tibiaandfibula Middleanddistalphalangesofeachtoe(exceptgreattoe)

Dorsiflexesandevertsfoot;extendstoes

Flexor digitorum longus(FLEK-sor) Tibia Distalphalangesofeachtoe(exceptgreattoe)

Plantarflexesfoot;flexestoes

Fibularis longusSoleusExtensordigitorum longus

Flexor digitorumlongus

Fibula

Fibula

TibiaTibialis anteriorGastrocnemius


Right lateral superficial view

Summary 185

Summary

The Body Contains Three Different Types of Muscular Tissue 154

•Therearethreetypesofmusculartissue:skeletal,cardiac,andsmooth,asshown.

Types of muscular tissues • Figure 6.1

•Skeletalmuscleisattachedtobones;itisstriatedandcanbevoluntarilycontrolled.

•Smoothmuscleislocatedinthewallsofholloworgans;itisnon-striatedandinvoluntary.

•Cardiacmuscleisfoundintheheart;itisstriatedandinvol-untary.

•Musculartissuecontractsandrelaxes,therebyproducingbodymovements,stabilizingbodypositions,regulatingorganvol-ume,movingsubstanceswithinthebody,andproducingheat.

1 2Muscles Are Built to Move 156

•Asshown,skeletalmusclesconsistofbundlesoffibers(cells),wrappedinconnectivetissue.Thefibersarelarge,cylindrical,andmulti-nucleated.Thecellmembranehastunnel-likeT-tu-bulesextendingintothecenterofthecell;therearenumerousmitochondria;andtheendoplasmicreticulum(sarcoplasmic �reticulum)iswelldevelopedandspecializedforstoringcal-cium.Thecellsarefilledwitharraysofmyofibrilsthatconsistofthickandthinfilamentsthatarearrangedintosarcomeres.Thickfilamentsaremadeoftheproteinmyosin,andthinfila-mentsaremadeofactin,tropomyosin,andtroponin.

The structure of a skeletal muscle and its connective tissue coverings • Figure 6.2

•Musclesshortenwhenthemyosininthickfilamentspullsontheactinofthinfilaments,therebycausingthemtoslidepastoneanother,towardthecenterofthesarcomere.Thisprocess,calledacontractioncycle,orcross-bridgecycle,istriggeredbyariseintheconcentrationofcalciumionsinthecytoplasm.

•Inaprocesscalledexcitation–contractioncoupling,anerveimpulsesetsupanelectrochemicalimpulsethatgetsconductedalongthemusclefiber.Thisimpulse,oraction �potential,isconducteddowntheT-tubulesandcausesthereleaseofcalciumionsfromthesarcoplasmicreticulum.Thecalciumionstriggerthecontractioncycle.Whenthecellrepolarizes,calciumgetspumpedbackintothesarcoplas-micreticulum,thecontractioncyclestops,andthemusclerelaxes.

•TheATPthatprovidestheenergyformusclecontractioncomesfromseveralsources,dependingontheamountoftimethemuscleremainscontracted:ATPandcreatinephos-phatereserves(0–15s),anaerobicrespirationorglycolysis(15–30s),andaerobicrespiration(lessthan30s).Workingmusclesneedgoodsuppliesofoxygenandbloodforsus-tainedactivity.Whenthemusclecannotcontractforcefully,itissaidtobefatigued.


Smooth muscle fiber

Branched cylindrical fiber, usually with one centrally located nucleus; intercalated discs join neighboringfibers; striated

Fiber is thickest in the middle, tapered at each end; has one centrally located nucleus; not striated


Long cylindrical fiber with many peripherally located nuclei; striated; unbranched

ThE PlAnnEr ✓✓

Sarcolemma

Sarcoplasm

Sarcoplasmic reticulum

Myofibril

Nucleus

Thin filamentThick filament

SarcomereZ disc

Mitochondrion

Triad:

Terminalcisterns

Transversetubule


Sarcolemma

Intermediatefilament

Dense body

Nucleus

Thick filament

Thin filament

Relaxed Contracted

AutonomicneuronsNucleus

Musclefibers

•Smoothmusclescanbestretchedconsiderablyandstillmaintaintheabilitytocontract,asshown.Thecontractionandrelaxationisslower,andthishelpsmaintainmuscletone.Smoothmusclescontractinresponsetonerveim-pulses,hormones,stretching,andlocalfactors.


•Asshown,thestructureofcardiacmusclehassomechar-acteristicsofsmoothmuscleandsomeofskeletalmuscle.Itisintermediateinsizebetweentheothermuscletypesandhascylindrical,branchedfibersthatareinterconnectedbyintercalated �discsthatcontaingapjunctions.Cardiacmusclecellshavelargemitochondria,onenucleus,andbundlesofmyofibrilsarrangedintosarcomeres.Theyhavewell-developedsarcoplasmicreticulumandT-tubulesys-tems,likeskeletalmuscle.

Structure of cardiac muscle cells • Figure 6.11

•Cardiaccellsrespondtosignalsfromspecializedheartmusclecellscalledpacemaker cells.Viapacemakercells,theautonomicnervoussystemcanspeeduporslowdownthecontractionofcardiaccellsasneeded.

•Asinglemusclecontractioniscalledatwitch,whileasus-tainedcontractioniscalledtetanus.Thetensiongeneratedbyamusclecanbeincreasedbyincreasingthefrequencyofnerveimpulsestothemotor �unit(viatemporalsummationorwavesummation)orbyincreasingthenumberofmotorunitsthatarecontractingatonetime(recruitment).

Smooth Muscle Tissue Is in the Walls of Most Organs 165

•Smoothmuscletissueiseithervisceral(single-unit)ormulti-unit,asshown.Smoothmusclecellsaremuchsmaller,thinner,andmorespindleshapedthanskeletalmuscle.Inadditiontothinandthickfilaments,smoothmusclecellshaveintermediatefilamentsattachedtodensebodies,form-inganet-likenetworkinthecell.Smoothmusclescellsdonothaveawell-developedsarcoplasmicreticulum.Visceralsmoothmusclecellscommunicatewitheachotherthroughgapjunctions.

Types and structure of smooth muscle cells • Figure 6.10

3 4

Cardiac cells areoften branched.

Cardiac cells have one large nucleus.

Sarcolemma (plasma membrane)

Cardiac cells are smaller than skeletal muscle fibers, but larger than smooth ones.

Cardiac cells have numerous, large mitochondria.

Intercalated discs are thickenings of plasma membrane where two cardiac cells come together. They hold cells together and aid in cell–cell communications.

Opening of T-tubule

Key Terms 187

relationships of muscles to bones • Figure 6.12

Skeletal Muscles Are Grouped Based on Location and Action 168

•Skeletalmusclesareattachedtoboneswithtendons.Theattachmentofamuscletoastationaryboneisitsorigin,theattachmenttoamovableboneisitsinsertion,andthepartofthemuscleinbetweenisthebelly,asshown.

•Musclesusuallyworkinpairsthathaveopposingactions.Themuscleactingastheagonist(prime �mover)contractstoproducethedesiredmovement,andtheantagonist �relaxes.Thesynergistworkswiththeprimemovertocausetheactionandhelpreduceunnecessarymovement,andthefixatorstabilizestheoriginoftheprimemoversoitcanworkmoreefficiently.

•Theprincipalskeletalmusclesaregroupedaccordingtoregion.Theirnamesindicatespecificcharacteristics,whicharebasedondescriptivecategoriessuchasdirectionoffibers,location,size,numberoforigins,shape,originandinsertionpoints,andaction.

5

Key Terms•actin169

•aerobicrespiration163

•agonist169

•anaerobicrespiration163

•antagonist169

•autorhythmic167

•belly168

•cardiacmuscletissue155

•contractionperiod163

•creatinephosphate163

•densebody165

•depolarization160

• fascicle157

• fastglycolytic(FG)fiber165

• fastoxidative-glycolytic(FOG)fiber165

•fixator169

•glycogen163

•glycolysis163

• insertion168

• intercalateddisc167

• intermediatefilament165

• isometriccontraction164

• isotoniccontraction164

• lacticacid163

• latentperiod163

•motorunit164

• multi-unitsmoothmuscletissue166

•muscletone164

•myofibril156

•myofilament158

•myoglobin163

•myosin169

•neuromuscularjunction160

•origin168

•primemover169

•relaxationperiod163

•repolarization160

•sarcomere156

•sarcoplasmicreticulum158

•skeletalmuscles154

•slowoxidative(SO)fiber165

•smoothmuscle155

•striated154

•synergist169

• temporalsummation164

• tetanus164

• thickfilament158

• thinfilament158

• transversetubule(T-tubule)158

• tropomyosin169

• troponin169

• twitch163

•visceral(single-unit)muscletissue166

•wavesummation164

Shoulder joint

Scapula

BELLYof tricepsbrachiimuscle

Tendon

Elbow joint

Ulna

BELLYof bicepsbrachiimuscle

Tendon

Radius

Tendons

STATIONARY BONE – For movement of the arm, this is the humerus.

INSERTION of biceps brachii on radius

ORIGIN of biceps brachii from scapula

ORIGIN of triceps brachii from scapula and humerus

INSERTION of triceps brachii on ulna

Movable bones


1.Rigormortisisastiffeningofallthemusclesinthebodythatoccursshortlyafterdeath.IthappenswhenalltheATPinthemusclesgetsusedup.Explainhowthisstiffeningoccurswithrespecttoaspectsofthecontractioncycle.

2.Drugscalledcalciumchannelblockershelprelaxthewallsofarteriesandveins,therebyloweringhighbloodpressure.Howdoesblockingacalciumchannelcausethemusclesofthearteriesandveinstorelax?

3.Thenightbeforeracing,mostmarathonrunnerseatmealsthatarehighincarbohydrates,likepasta.Explainhowthis“carbingup”helpstheirmusclesduringtherace.

Critical and Creative Thinking Questions4.Jimliftsahandweightbymovinghiselbowandsubsequently

lowersit.Listthemusclesinvolvedineachmotionandexplainwhichonesaretheprimemovers,antagonists,synergists,andfixators.

5.Celiaistrainingtoruna10krace.Shestretchesandexercisesdailyformonths.Explainwhyshemuststretch.Whatchangeswilloccurtothestructureofherlegmusclesasaresultofhertraining?

Manyathletescomplainaboutsorenessafteranextensiveworkout.Sometimesmassagecanhelp.

What is happening in this picture?

1.Whatshouldathletesdobeforeexercisetopreventorminimizeinjury?2.Whatbiochemicalorphysiologicalaspectsofmusclecontractioncausemusclesorenessfollowingexercise?

T h i n k C r i t i c a l l y

2.Thisfigureshows_______muscletissue.

a.skeletal c.smooth

b.cardiac d.synergist

3.Whatarethestructuresindicatedbythe?inthefigure?

a.Z-lines c.nuclei

b.striations d.intercalateddiscs

4.Thecellsinthefigurearecapableof_______.

a.twitchonly c.fusedtetanus

b.unfusedtetanus d.wavesummation

Self-Test(CheckyouranswersinAppendixC.)

1.Thefirstenergysourceusedinaworkingmuscleis_______.

a.aerobicrespiration

b.glycolysis

c.ATP

d.creatinephosphate

Usethisfiguretoanswerquestions2–4.

ReviewyourChapterPlanneronthechapteropenerandcheckoffyourcompletedwork.

ThE PlAnnEr ✓✓

Self-Test 189


11.Thecellsinthefigureregulatecontractionbyplacingaphosphategroupon_______.

a.myosin

b.actin

c.troponin

d.tropomyosin

12.Wherewouldyoufindthearrangementofmusclefibersshowninthisfigure?

a.bicepsmuscle

b.heart

c.bronchialairway

d.urinarybladder

13.The_______stabilizestheinsertionpointofaskeletalmuscle.

a.agonistmuscle

b.antagonistmuscle

c.synergist

d.fixator

14.The_______assistsinbreathing.

a.soleus

b.latissimusdorsi

c.externalintercostal

d.extensordigitorum

15.The_______haswhitefibers.

a.uterus

b.heart

c.biceps

d.bladder

5.Whichofthefollowingisnottrueofsmoothmuscletissue?

a.Itcanmaintainsteadycontractionsforalongtime.

b.Contractionsareinvoluntary.

c.Ithasmultiplenuclei.

d.Itisfoundinthewallsofallholloworgans.

6.Thebicepsbrachiimusclehelpstoflextheelbow.Theendofthismusclethatattachestothehumerusiscalledthe_______.

a.insertion

b.origin

c.belly

d.tendon

7.Whatisthelargestskeletalmusclefiber?

a.slowoxidativefiber

b.fastglycolyticfiber

c.slowglycolyticfiber

d.fastoxidative-glycolyticfiber


8.Inwhichlabeledstructurewouldyoufindactin?

a.A c.C

b.B d.D

9.WhichstructurecontainstheZ-disc?

a.A c.C

b.B d.D

10.WhichlabelrepresentstheA-band?

a.A c.C

b.B d.D

C CB

DA

Documents

Visualizing A&P Sample Chapter