© 2012 Pearson Education, Inc. An Introduction to Muscle Tissue Muscle Tissue A primary tissue type, divided into: Skeletal muscle tissue Cardiac muscle

© 2012 Pearson Education, Inc.

An Introduction to Muscle Tissue

• Muscle Tissue

• A primary tissue type, divided into:

• Skeletal muscle tissue

• Cardiac muscle tissue

• Smooth muscle tissue


10-1 Functions of Skeletal Muscle Tissue

• Skeletal Muscles

• Are attached to the skeletal system

• Allow us to move

• The muscular system

• Includes only skeletal muscles


10-1 Functions of Skeletal Muscle Tissue

• Six Functions of Skeletal Muscle Tissue

1. Produce skeletal movement

2. Maintain posture and body position

3. Support soft tissues

4. Guard entrances and exits

5. Maintain body temperature

6. Store nutrient reserves


10-2 Organization of Muscle

• Organization of Connective Tissues

• Muscles have three layers of connective tissues

1. Epimysium

2. Perimysium

3. Endomysium



• Epimysium

• Exterior collagen layer

• Connected to deep fascia

• Separates muscle from surrounding tissues



• Perimysium

• Surrounds muscle fiber bundles (fascicles)

• Contains blood vessel and nerve supply to

fascicles



• Endomysium

• Surrounds individual muscle cells (muscle fibers)

• Contains capillaries and nerve fibers contacting

muscle cells

• Contains myosatellite cells (stem cells) that repair

damage


Figure 10-1 The Organization of Skeletal Muscles

Skeletal Muscle (organ)

Musclefascicle

Musclefibers

Bloodvessels

Epimysium Perimysium Endomysium

Nerve

Epimysium

Blood vesselsand nerves

Endomysium

Perimysium

Tendon



Epimysium


Endomysium

Perimysium

Tendon

Muscle Fascicle (bundle of fibers)

Perimysium

Muscle fiber

Endomysium



Epimysium


Endomysium

Perimysium

Tendon

Muscle Fiber (cell)Endomysium

Sarcoplasm

Mitochondrion

MyosatellitecellSarcolemmaNucleus

Capillary Myofibril

Axon of neuron



• Organization of Connective Tissues

• Muscle Attachments

• Endomysium, perimysium, and epimysium come

together:

• At ends of muscles

• To form connective tissue attachment to bone

matrix

• I.e., tendon (bundle) or aponeurosis (sheet)



• Blood Vessels and Nerves

• Muscles have extensive vascular systems that:

• Supply large amounts of oxygen

• Supply nutrients

• Carry away wastes

• Skeletal muscles are voluntary muscles, controlled

by nerves of the central nervous system (brain and

spinal cord)


10-3 Characteristics of Skeletal Muscle Fibers

• Skeletal Muscle Cells

• Are very long

• Develop through fusion of mesodermal cells

(myoblasts)

• Become very large

• Contain hundreds of nuclei


Figure 10-2 The Formation of a Multinucleate Skeletal Muscle Fiber

Muscle fibers developthrough the fusion ofmesodermal cellscalled myoblasts.

Myoblasts

A muscle fiber formsby thefusion ofmyoblasts.

A diagrammatic view and amicrograph of one muscle fiber.

Up to 30 cmin length

Myosatellite cell

Nuclei

Immaturemuscle fiber

Myofibrils

Mitochondria

Myosatellite cell

Mature muscle fiber

SarcolemmaNuclei

Muscle fiber LM 612


Figure 10-2a The Formation of a Multinucleate Skeletal Muscle Fiber

Muscle fibers developthrough the fusion ofmesodermal cellscalled myoblasts.

Myoblasts

A muscle fiber formsby thefusion ofmyoblasts.

Up to 30 cmin length

Myosatellite cell

Nuclei

Immaturemuscle fiber

Myosatellite cell

Mature muscle fiber


Figure 10-2b The Formation of a Multinucleate Skeletal Muscle Fiber

A diagrammatic view and amicrograph of one muscle fiber.

Myofibrils

Mitochondria

SarcolemmaNuclei

Muscle fiber LM 612



• The Sarcolemma and Transverse Tubules

• The sarcolemma

• The cell membrane of a muscle fiber (cell)

• Surrounds the sarcoplasm (cytoplasm of muscle

fiber)

• A change in transmembrane potential begins

contractions



• The Sarcolemma and Transverse Tubules

• Transverse tubules (T tubules)

• Transmit action potential through cell

• Allow entire muscle fiber to contract

simultaneously

• Have same properties as sarcolemma



• Myofibrils

• Lengthwise subdivisions within muscle fiber

• Made up of bundles of protein filaments (myofilaments)

• Myofilaments are responsible for muscle contraction

• Types of myofilaments:

• Thin filaments

• Made of the protein actin

• Thick filaments

• Made of the protein myosin



• The Sarcoplasmic Reticulum (SR)

• A membranous structure surrounding each myofibril

• Helps transmit action potential to myofibril

• Similar in structure to smooth endoplasmic reticulum

• Forms chambers (terminal cisternae) attached to T

tubules



• The Sarcoplasmic Reticulum (SR)

• Triad

• Is formed by one T tubule and two terminal

cisternae

• Cisternae

• Concentrate Ca2+ (via ion pumps)

• Release Ca2+ into sarcomeres to begin muscle

contraction


Figure 10-3 The Structure of a Skeletal Muscle Fiber

Myofibril

Sarcolemma

Sarcoplasm

Nuclei

MUSCLE FIBER

Mitochondria

Sarcolemma

Myofibril

Thin filament

Thick filamentTriad Sarcoplasmic

reticulumT tubules

Myofibrils

Sarcoplasm

Sarcolemma

Terminal cisterna


Figure 10-3 The Structure of a Skeletal Muscle Fiber

Triad Sarcoplasmicreticulum

T tubules

Myofibrils

Sarcoplasm

Sarcolemma

Terminal cisterna


10-3 Structural Components of a Sarcomere

• Sarcomeres

• The contractile units of muscle

• Structural units of myofibrils

• Form visible patterns within myofibrils

• A striped or striated pattern within myofibrils

• Alternating dark, thick filaments (A bands) and light,

thin filaments (I bands)


Figure 10-4a Sarcomere Structure, Part I

A longitudinalsection of asarcomere,showing bands

I band A band

H band Z line Titin

Zone of overlap M line

Sarcomere

Thinfilament

Thickfilament


Figure 10-4b Sarcomere Structure, Part I

A correspondingview of a sarcomere in a myofibril from amuscle fiber in thegastrocnemiusmuscle of the calf

I band A band

H band Z line

Zone of overlap M line

Sarcomere

Z line

Myofibril TEM 64,000


Figure 10-5 Sarcomere Structure, Part II

Myofibril

Sarcomere

Thinfilament

Thickfilament

Titinfilament

Actininfilaments

Attachmentof titin

Z line I band M line H band Zone of overlap

A superficial viewof a sarcomere

Cross-sectional views of differentportions of a sarcomere


Figure 10-6 Levels of Functional Organization in a Skeletal Muscle

Skeletal Muscle

Muscle Fascicle

Muscle Fiber

Myofibril

Sarcomere

Epimysium

Surrounded by:Epimysium

Contains:Muscle fascicles

Perimysium

Surrounded by:Perimysium

Contains:Muscle fibers

Endomysium Surrounded by:Endomysium

Contains:Myofibrils

Surrounded by:Sarcoplasmicreticulum

Consists of:Sarcomeres(Z line to Z line)

Contains:Thick filaments

Thin filaments

Z lineTitinM lineZ line

H band

I band A band


Figure 10-7ab Thick and Thin Filaments

Z line M line

Myofibril

H band

Sarcomere

Troponin Active site Nebulin Tropomyosin G-actinmolecules

F-actinstrand

Actinin Z line Titin

The gross structure of a thinfilament, showing theattachment at the Z line

The organization of G-actin subunitsin an F-actin strand, and the positionof the troponin–tropomyosin complex



• Initiating Contraction

• Ca2+ binds to receptor on troponin molecule

• Troponin–tropomyosin complex changes

• Exposes active site of F-actin



• Thick Filaments

• Contain about 300 twisted myosin subunits

• Contain titin strands that recoil after stretching

• The mysosin molecule

• Tail

• Binds to other myosin molecules

• Head

• Made of two globular protein subunits

• Reaches the nearest thin filament


Figure 10-7cd Thick and Thin Filaments

Titin

Myosinhead

HingeMyosin tail

The structure of a myosin molecule

M lineThe structure of thick filaments, showing the orientation of themyosin molecules



• Myosin Action

• During contraction, myosin heads:

• Interact with actin filaments, forming cross-

bridges

• Pivot, producing motion



• Sliding Filaments and Muscle Contraction

• Sliding filament theory

• Thin filaments of sarcomere slide toward M line,

alongside thick filaments

• The width of A zone stays the same

• Z lines move closer together


Figure 10-8a Changes in the Appearance of a Sarcomere during the Contraction of a Skeletal Muscle Fiber

A bandI band

Z line H band Z line

A relaxed sarcomere showing location of the A band, Z lines, and I band.


Figure 10-8b Changes in the Appearance of a Sarcomere during the Contraction of a Skeletal Muscle Fiber

Z line Z line

A bandI band

H band

During a contraction, the A band stays thesame width, but the Z lines move closertogether and the I band gets smaller. Whenthe ends of a myofibril are free to move,the sarcomeres shorten simultaneouslyand the ends of the myofibril are pulledtoward its center.



• Skeletal Muscle Contraction

• The process of contraction

• Neural stimulation of sarcolemma

• Causes excitation–contraction coupling

• Muscle fiber contraction

• Interaction of thick and thin filaments

• Tension production


Figure 10-9 An Overview of Skeletal Muscle Contraction

Neural control

Excitation–contraction coupling

Excitation

ATP

Calciumrelease

Thick-thinfilament interaction

triggers

Muscle fibercontraction

Tensionproduction

leads to


10-4 Components of the Neuromuscular Junction

• The Control of Skeletal Muscle Activity

• The neuromuscular junction (NMJ)

• Special intercellular connection between the

nervous system and skeletal muscle fiber

• Controls calcium ion release into the sarcoplasm

A&P FLIX Events at the Neuromuscular Junction


Figure 10-11 Skeletal Muscle Innervation

Synapticterminal

Neuromuscularjunction

Sarcoplasmicreticulum

Motorend plate

Myofibril

SEE BELOW

Motor end plate

Path of electrical impulse(action potential)

Motor neuron

Axon



The synaptic cleft, anarrow space, separatesthe synaptic terminal of

the neuron from theopposing motor end

plate.Junctional

fold ofmotor end plate

AChE

Vesicles ACh

The cytoplasm of the synapticterminal contains vesiclesfilled with molecules ofacetylcholine, or ACh.Acetylcholine is aneurotransmitter, a chemicalreleased by a neuron to changethe permeability or otherproperties of another cell’s plasma membrane. The synaptic cleft and themotor end plate containmolecules of the enzymeacetylcholinesterase (AChE),which breaks down ACh.



Arriving actionpotential

The stimulus for ACh releaseis the arrival of an electricalimpulse, or action potential,at the synaptic terminal. Anaction potential is a suddenchange in the transmembranepotential that travels alongthe length of the axon.



When the action potentialreaches the neuron’s synapticterminal, permeabilitychanges in the membranetrigger the exocytosis of AChinto the synaptic cleft.Exocytosis occurs as vesiclesfuse with the neuron’s plasmamembrane.

Motorend plate



AChreceptor site

ACh molecules diffuseacross the synatpic cleft andbind to ACh receptors on thesurface of the motor endplate. ACh binding alters themembrane’s permeability tosodium ions. Because theextracellular fluid contains ahigh concentration ofsodium ions, and sodium ion concentration inside thecell is very low, sodium ionsrush into the sarcoplasm.



The sudden inrush ofsodium ions results in thegeneration of an actionpotential in thesarcolemma. AChE quicklybreaks down the ACh onthe motor end plate and inthe synaptic cleft, thusinactivating the AChreceptor sites.

Actionpotential

AChE


10-4 Components of the Neuromuscular Junction

• Excitation–Contraction Coupling

• Action potential reaches a triad

• Releasing Ca2+

• Triggering contraction

• Requires myosin heads to be in “cocked” position

• Loaded by ATP energy

A&P FLIX Excitation-Contraction Coupling


Figure 10-10 The Exposure of Active Sites

In a resting sarcomere, thetropomyosin strands coverthe active sites on the thinfilaments, preventingcross-bridge formation.

When calcium ions enterthe sarcomere, they bindto troponin, whichrotates and swings thetropomyosin away fromthe active sites.

Cross-bridgeformation then occurs,and the contractioncycle begins.

SARCOPLASMIC RETICULUM

Calcium channelsopen

Troponin

NebulinActive site

G-actin(thin filament)

Tropomyosinstrand

Myosin tail(thick filament)


10-4 Skeletal Muscle Contraction

• The Contraction Cycle

1. Contraction Cycle Begins

2. Active-Site Exposure

3. Cross-Bridge Formation

4. Myosin Head Pivoting

5. Cross-Bridge Detachment

6. Myosin Reactivation

A&P FLIX The Cross Bridge Cycle


Figure 10-12 The Contraction Cycle

Myosin head

Troponin

Tropomyosin Actin

The contraction cycle, whichinvolves a series of interrelatedsteps, begins with the arrival ofcalcium ions within the zone ofoverlap.

Contraction Cycle Begins



Calcium ions bind to troponin,weakening the bond betweenactin and the troponin–tropomyosin complex. Thetroponin molecule then changesposition, rolling the tropomyosinmolecule away from the activesites on actin and allowinginteraction with the energizedmyosin heads.

Active-Site Exposure

Sarcoplasm

Activesite



Once the active sites areexposed, the energizedmyosin heads bind to them,forming cross-bridges.

Cross-Bridge Formation



After cross-bridge formation,the energy that was stored inthe resting state is releasedas the myosin head pivotstoward the M line. This actionis called the power stroke;when it occurs, the boundADP and phosphate groupare released.

Myosin Head Pivoting



When another ATP binds tothe myosin head, the linkbetween the myosin head andthe active site on the actinmolecule is broken. Theactive site is now exposedand able to form anothercross-bridge.

Cross-Bridge Detachment



Myosin reactivationoccurs when the freemyosin head splits ATPinto ADP and P. Theenergy released is used torecock the myosin head.

Myosin Reactivation


10-4 Skeletal Muscle Contraction

• Fiber Shortening

• As sarcomeres shorten, muscle pulls together,

producing tension

• Muscle shortening can occur at both ends of the

muscle, or at only one end of the muscle

• This depends on the way the muscle is attached at

the ends


Figure 10-13 Shortening during a Contraction

When both ends are free to move, the ends of acontracting muscle fiber move toward the center ofthe muscle fiber.

When one end of a myofibril is fixed in position, andthe other end free to move, the free end is pulledtoward the fixed end.


10-4 Skeletal Muscle Relaxation

• Relaxation

• Contraction Duration

• Depends on:

• Duration of neural stimulus

• Number of free calcium ions in sarcoplasm

• Availability of ATP


10-4 Skeletal Muscle Relaxation

• Relaxation

• Ca2+ concentrations fall

• Ca2+ detaches from troponin

• Active sites are re-covered by tropomyosin

• Rigor Mortis

• A fixed muscular contraction after death

• Caused when:

• Ion pumps cease to function; ran out of ATP

• Calcium builds up in the sarcoplasm


10-4 Skeletal Muscle Contraction and Relaxation

• Summary

• Skeletal muscle fibers shorten as thin filaments slide between thick filaments

• Free Ca2+ in the sarcoplasm triggers contraction

• SR releases Ca2+ when a motor neuron stimulates the muscle fiber

• Contraction is an active process

• Relaxation and return to resting length are passive


Table 10-1 Steps Involved in Skeletal Muscle Contraction and Relaxation

Steps in Initiating Muscle Contraction

ACh released, bindingto receptors

Synapticterminal

Motorend plate T tubule Sarcolemma

ActionpotentialreachesT tubule

Sarcoplasmicreticulumreleases Ca2

Ca2

Actin

Myosin

Active siteexposure,cross-bridge formation

Contractionbegins

Steps in Muscle Relaxation

ACh broken down by AChE

Sarcoplasmicreticulumrecaptures Ca2

Active sites covered, nocross-bridgeinteraction

Contractionends

Relaxation occurs,passive return toresting length


10-5 Tension Production and Contraction Types

• Tension Production by Muscles Fibers

• As a whole, a muscle fiber is either contracted or

relaxed

• Depends on:

• The number of pivoting cross-bridges

• The fiber’s resting length at the time of stimulation

• The frequency of stimulation


Figure 10-14 The Effect of Sarcomere Length on Active Tension

Normalrange

Decreased length Increased sarcomere length

Ten

sio

n (

per

cen

t o

f m

axim

um

)

Optimal resting length:The normal range of

sarcomere lengths in thebody is 75 to 130 percent of

the optimal length.




• The Frequency of Stimulation

• A single neural stimulation produces:

• A single contraction or twitch

• Which lasts about 7–100 msec.

• Sustained muscular contractions

• Require many repeated stimuli




• Twitches

1. Latent period

• The action potential moves through sarcolemma

• Causing Ca2+ release

2. Contraction phase

• Calcium ions bind

• Tension builds to peak

3. Relaxation phase

• Ca2+ levels fall

• Active sites are covered and tension falls to resting levels


Figure 10-15a The Development of Tension in a Twitch

Eye muscle

Soleus

GastrocnemiusT

ensi

on

Time (msec)Stimulus

A myogram showing differences intension over time for a twitch in different skeletal muscles.


Figure 10-15b The Development of Tension in a Twitch

Te

ns

ion

The details of tension over time for a single twitch in the gastrocnemius muscle. Notice the presence of a latent period, which corresponds to the time needed for the conduction of an action potential and the subsequent release of calcium ions by the sarcoplasmic reticulum.

Stimulus

Maximum tensiondevelopment

Restingphase

Latentperiod

Contractionphase

Relaxationphase




• Treppe

• A stair-step increase in twitch tension

• Repeated stimulations immediately after relaxation

phase

• Stimulus frequency <50/second

• Causes a series of contractions with increasing

tension




• Wave summation

• Increasing tension or summation of twitches

• Repeated stimulations before the end of relaxation

phase

• Stimulus frequency >50/second

• Causes increasing tension or summation of

twitches


Figure 10-16ab Effects of Repeated Stimulations

Maximum tension (in tetanus)

Maximum tension (in treppe)

Ten

sio

n

Time

Treppe. Treppe is an increase inpeak tension with each successive stimulus delivered shortly after the completion of the relaxation phase of the preceding twitch.

Stimulus

Time

Wave summation. Wavesummation occurs whensuccessive stimuli arrivebefore the relaxation phasehas been completed.




• Incomplete tetanus

• Twitches reach maximum tension

• If rapid stimulation continues and muscle is not allowed to relax, twitches reach maximum level of tension

• Complete tetanus

• If stimulation frequency is high enough, muscle never begins to relax, and is in continuous contraction


Figure 10-16cd Effects of Repeated Stimulations

Ten

sio

n

Maximum tension (in tetanus)

Time Time

Complete tetanus. Duringcomplete tetanus, the stimulusfrequency is so high that therelaxation phase is eliminated;tension plateaus at maximallevels.

Incomplete tetanus. Incomplete tetanus occurs if the stimulus frequency increases further. Tension production rises to a peak, and the periods of relaxation are very brief.



• Tension Production by Skeletal Muscles

• Depends on:

• Internal tension produced by muscle fibers

• External tension exerted by muscle fibers on

elastic extracellular fibers

• Total number of muscle fibers stimulated



• Motor Units and Tension Production

• Motor units in a skeletal muscle:

• Contain hundreds of muscle fibers

• That contract at the same time

• Controlled by a single motor neuron




• Recruitment (multiple motor unit summation)

• In a whole muscle or group of muscles, smooth motion and increasing tension are produced by slowly increasing the size or number of motor units stimulated

• Maximum tension

• Achieved when all motor units reach tetanus

• Can be sustained only a very short time


Figure 10-17a The Arrangement and Activity of Motor Units in a Skeletal Muscle

SPINAL CORD

Axons ofmotor neurons

Motornerve

Muscle fibersKEY

Motor unit 1

Motor unit 2

Motor unit 3

Muscle fibers of different motor units areintermingled, so the forces applied to thetendon remain roughly balanced regardless ofwhich motor units are stimulated.


Figure 10-17b The Arrangement and Activity of Motor Units in a Skeletal Muscle

Motorunit 1

Motorunit 2

Motorunit 3

Tension in tendon

Ten

sio

n

Time

The tension applied to thetendon remains relativelyconstant, even thoughindividual motor units cyclebetween contraction andrelaxation.




• Sustained tension

• Less than maximum tension

• Allows motor units rest in rotation

• Muscle tone

• The normal tension and firmness of a muscle at rest

• Muscle units actively maintain body position, without motion

• Increasing muscle tone increases metabolic energy used, even at rest




• Contraction are classified based on pattern of

tension production

• Isotonic contraction

• Isometric contraction



• Isotonic Contraction

• Skeletal muscle changes length

• Resulting in motion

• If muscle tension > load (resistance):

• Muscle shortens (concentric contraction)

• If muscle tension < load (resistance):

• Muscle lengthens (eccentric contraction)


Figure 10-18a Concentric, Eccentric, and Isometric Contractions

Tendon

Musclecontracts

(concentriccontraction)

2 kg

2 kg

Musclelength(percentof restinglength)

Time

Muscletension

(kg)

Amount ofload

Musclerelaxes

Contractionbegins Resting length

Peak tensionproduction


Figure 10-18b Concentric, Eccentric, and Isometric Contractions

Support removedwhen contraction

begins(eccentric contraction)


Muscletension

(kg)


Resting length

Time

Support removed,contraction begins

6 kg

6 kg



• Isometric Contraction

• Skeletal muscle develops tension, but is

prevented from changing length

• iso- = same, metric = measure


Figure 10-18c Concentric, Eccentric, and Isometric Contractions

Musclecontracts(isometric

contraction)

6 kg 6 kg

Muscletension

(kg)


Amount of load

Length unchanged


Contractionbegins

Musclerelaxes

Time



• Muscle Relaxation and the Return to Resting Length

• Elastic Forces

• The pull of elastic elements (tendons and ligaments)

• Expands the sarcomeres to resting length

• Opposing Muscle Contractions

• Reverse the direction of the original motion

• Are the work of opposing skeletal muscle pairs



• Muscle Relaxation and the Return to Resting

Length

• Gravity

• Can take the place of opposing muscle contraction

to return a muscle to its resting state


10-6 Energy to Power Contractions

• ATP Provides Energy For Muscle Contraction

• Sustained muscle contraction uses a lot of ATP

energy

• Muscles store enough energy to start contraction

• Muscle fibers must manufacture more ATP as

needed



• ATP and CP Reserves

• Adenosine triphosphate (ATP)

• The active energy molecule

• Creatine phosphate (CP)

• The storage molecule for excess ATP energy in resting muscle

• Energy recharges ADP to ATP

• Using the enzyme creatine kinase (CK)

• When CP is used up, other mechanisms generate ATP



• ATP Generation

• Cells produce ATP in two ways

1. Aerobic metabolism of fatty acids in the

mitochondria

2. Anaerobic glycolysis in the cytoplasm



• Aerobic Metabolism

• Is the primary energy source of resting muscles

• Breaks down fatty acids

• Produces 34 ATP molecules per glucose molecule

• Glycolysis

• Is the primary energy source for peak muscular activity

• Produces two ATP molecules per molecule of glucose

• Breaks down glucose from glycogen stored in skeletal muscles


Table 10-2 Sources of Energy in a Typical Muscle Fiber



• Energy Use and the Level of Muscular Activity

• Skeletal muscles at rest metabolize fatty acids and store glycogen

• During light activity, muscles generate ATP through anaerobic breakdown of carbohydrates, lipids, or amino acids

• At peak activity, energy is provided by anaerobic reactions that generate lactic acid as a byproduct


Figure 10-20 Muscle Metabolism

Fatty acids Blood vessels

Glucose Glycogen

MitochondriaCreatine

Resting muscle: Fatty acids are catabolized; theATP produced is used to build energy reserves of ATP,CP, and glycogen.

Moderate activity: Glucose and fatty acids arecatabolized; the ATP produced is used to powercontraction.

Glycogen

Fatty acids

Glucose

Pyruvate

To myofibrils to support muscle contraction

GlycogenGlucose

PyruvateCreatine

Lactate

Lactate

To myofibrils to support muscle contraction

Peak activity: Most ATP is produced through glycolysis,with lactate as a by-product. Mitochondrial activity(not shown) now provides only about one-third of the ATP consumed.



• Muscle Fatigue

• When muscles can no longer perform a required activity, they are fatigued

• Results of Muscle Fatigue

• Depletion of metabolic reserves

• Damage to sarcolemma and sarcoplasmic reticulum

• Low pH (lactic acid)

• Muscle exhaustion and pain



• The Recovery Period

• The time required after exertion for muscles to

return to normal

• Oxygen becomes available

• Mitochondrial activity resumes



• Lactic Acid Removal and Recycling

• The Cori Cycle

• The removal and recycling of lactic acid by the liver

• Liver converts lactate to pyruvate

• Glucose is released to recharge muscle glycogen

reserves



• The Oxygen Debt

• After exercise or other exertion:

• The body needs more oxygen than usual to normalize

metabolic activities

• Resulting in heavy breathing

• Also called excess postexercise oxygen

consumption (EPOC)



• Heat Production and Loss

• Active muscles produce heat

• Up to 70% of muscle energy can be lost as heat,

raising body temperature



• Hormones and Muscle Metabolism

• Growth hormone

• Testosterone

• Thyroid hormones

• Epinephrine


10-7 Types of Muscles Fibers and Endurance

• Muscle Performance

• Force

• The maximum amount of tension produced

• Endurance

• The amount of time an activity can be sustained

• Force and endurance depend on:

• The types of muscle fibers

• Physical conditioning



• Three Major Types of Skeletal Muscle Fibers

1. Fast fibers

2. Slow fibers

3. Intermediate fibers



• Fast Fibers

• Contract very quickly

• Have large diameter, large glycogen reserves,

few mitochondria

• Have strong contractions, fatigue quickly



• Slow Fibers

• Are slow to contract, slow to fatigue

• Have small diameter, more mitochondria

• Have high oxygen supply

• Contain myoglobin (red pigment, binds oxygen)



• Intermediate Fibers

• Are mid-sized

• Have low myoglobin

• Have more capillaries than fast fibers, slower to

fatigue


Figure 10-21 Fast versus Slow Fibers

Slow fibersSmaller diameter,

darker color due tomyoglobin; fatigue

resistant

Fast fibersLarger diameter,

paler color;easily fatigued

LM 170

LM 170 LM 783


Table 10-3 Properties of Skeletal Muscle Fiber Types



• Muscle Performance and the Distribution of Muscle Fibers

• White muscles

• Mostly fast fibers

• Pale (e.g., chicken breast)

• Red muscles

• Mostly slow fibers

• Dark (e.g., chicken legs)

• Most human muscles

• Mixed fibers

• Pink



• Muscle Hypertrophy

• Muscle growth from heavy training

• Increases diameter of muscle fibers

• Increases number of myofibrils

• Increases mitochondria, glycogen reserves

• Muscle Atrophy

• Lack of muscle activity

• Reduces muscle size, tone, and power



• Physical Conditioning

• Improves both power and endurance

• Anaerobic activities (e.g., 50-meter dash,

weightlifting)

• Use fast fibers

• Fatigue quickly with strenuous activity

• Improved by:

• Frequent, brief, intensive workouts

• Causes hypertrophy



• Physical Conditioning

• Improves both power and endurance

• Aerobic activities (prolonged activity)

• Supported by mitochondria

• Require oxygen and nutrients

• Improves:

• Endurance by training fast fibers to be more like

intermediate fibers

• Cardiovascular performance



• Importance of Exercise

• What you don’t use, you lose

• Muscle tone indicates base activity in motor units of skeletal muscles

• Muscles become flaccid when inactive for days or weeks

• Muscle fibers break down proteins, become smaller and weaker

• With prolonged inactivity, fibrous tissue may replace muscle fibers

Documents

© 2012 Pearson Education, Inc. An Introduction to Muscle Tissue Muscle Tissue A primary tissue type, divided into: Skeletal muscle tissue Cardiac muscle