11

Chapter 11Chapter 11

Lecture OutlineLecture Outline

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22

Muscle TissueMuscle Tissue

Types and characteristics of muscular tissueTypes and characteristics of muscular tissue Microscopic anatomy of skeletal muscleMicroscopic anatomy of skeletal muscle Nerve-Muscle relationshipNerve-Muscle relationship Behavior of skeletal muscle fibersBehavior of skeletal muscle fibers Behavior of whole musclesBehavior of whole muscles Muscle metabolismMuscle metabolism Cardiac and smooth muscleCardiac and smooth muscle

33

Introduction to MuscleIntroduction to Muscle Movement is a fundamental characteristic of Movement is a fundamental characteristic of

all living thingsall living things Cells capable of shortening and converting Cells capable of shortening and converting

the chemical energy of ATP into mechanical the chemical energy of ATP into mechanical energy energy

Types of muscleTypes of muscle skeletal, cardiac and smoothskeletal, cardiac and smooth

Physiology of skeletal musclePhysiology of skeletal muscle basis of warm-up, strength, endurance and basis of warm-up, strength, endurance and

fatiguefatigue

44

Characteristics of MuscleCharacteristics of Muscle Responsiveness (excitability)Responsiveness (excitability)

to chemical signals, stretch and electrical to chemical signals, stretch and electrical changes across the plasma membranechanges across the plasma membrane

ConductivityConductivity local electrical change triggers a wave of local electrical change triggers a wave of

excitation that travels along the muscle fiberexcitation that travels along the muscle fiber Contractility -- shortens when stimulatedContractility -- shortens when stimulated Extensibility -- capable of being stretchedExtensibility -- capable of being stretched Elasticity -- returns to its original resting length Elasticity -- returns to its original resting length

after being stretchedafter being stretched

55

Skeletal MuscleSkeletal Muscle Voluntary striated muscle attached to bonesVoluntary striated muscle attached to bones Muscle fibers (myofibers) as long as 30 cmMuscle fibers (myofibers) as long as 30 cm Exhibits alternating light and dark transverse Exhibits alternating light and dark transverse

bands or striationsbands or striations reflects overlapping arrangement of reflects overlapping arrangement of

internal contractile proteinsinternal contractile proteins Under conscious Under conscious

control (voluntary)control (voluntary)

66

Connective Tissue ElementsConnective Tissue Elements Attachments between muscle and boneAttachments between muscle and bone

endomysium, perimysium, epimysium, fascia, endomysium, perimysium, epimysium, fascia, tendontendon

Collagen is extensible and elasticCollagen is extensible and elastic stretches slightly under tension and recoils when stretches slightly under tension and recoils when

releasedreleased• protects muscle from injuryprotects muscle from injury• returns muscle to its resting lengthreturns muscle to its resting length

Elastic componentsElastic components parallel components parallel muscle cellsparallel components parallel muscle cells series components joined to ends of muscleseries components joined to ends of muscle

77

The Muscle FiberThe Muscle Fiber

88

Muscle FibersMuscle Fibers

Multiple flattened nuclei inside cell Multiple flattened nuclei inside cell membranemembrane fusion of multiple myoblasts during developmentfusion of multiple myoblasts during development unfused satellite cells nearby can multiply to unfused satellite cells nearby can multiply to

produce a small number of new myofibers produce a small number of new myofibers Sarcolemma has tunnel-like infoldings or Sarcolemma has tunnel-like infoldings or

transverse (T) tubules that penetrate the celltransverse (T) tubules that penetrate the cell carry electric current to cell interiorcarry electric current to cell interior

99

Muscle Fibers 2Muscle Fibers 2

Sarcoplasm is filled with Sarcoplasm is filled with myofibrils (bundles of myofilaments)myofibrils (bundles of myofilaments) glycogen for stored energy and myoglobin for glycogen for stored energy and myoglobin for

binding oxygenbinding oxygen Sarcoplasmic reticulum = smooth ERSarcoplasmic reticulum = smooth ER

network around each myofibrilnetwork around each myofibril dilated end-sacs (terminal cisternea) store dilated end-sacs (terminal cisternea) store

calciumcalcium triad = T tubule and 2 terminal cisterneatriad = T tubule and 2 terminal cisternea

1010

Thick FilamentsThick Filaments

Made of 200 to 500 myosin moleculesMade of 200 to 500 myosin molecules 2 entwined polypeptides (golf clubs)2 entwined polypeptides (golf clubs)

Arranged in a bundle with heads directed Arranged in a bundle with heads directed outward in a spiral array around the bundled outward in a spiral array around the bundled tailstails central area is a bare zone with no headscentral area is a bare zone with no heads

1111

Thin FilamentsThin Filaments Two intertwined strands fibrous (F) actin Two intertwined strands fibrous (F) actin

globular (G) actin with an active siteglobular (G) actin with an active site Groove holds tropomyosin moleculesGroove holds tropomyosin molecules

each blocking 6 or 7 active sites of G actinseach blocking 6 or 7 active sites of G actins One small, calcium-binding troponin One small, calcium-binding troponin

molecule on each tropomyosin moleculemolecule on each tropomyosin molecule

1212

Elastic FilamentsElastic Filaments

Springy proteins called titinSpringy proteins called titin Anchor each thick filament to Z discAnchor each thick filament to Z disc Prevents overstretching of sarcomerePrevents overstretching of sarcomere

1313

Regulatory and Contractile ProteinsRegulatory and Contractile Proteins

Myosin and actin are contractile proteinsMyosin and actin are contractile proteins Tropomyosin and troponin = regulatory proteinsTropomyosin and troponin = regulatory proteins

switch that starts and stops shortening of muscle cellswitch that starts and stops shortening of muscle cell contraction activated by release of calcium into sarcoplasm and contraction activated by release of calcium into sarcoplasm and

its binding to troponin, its binding to troponin, troponin moves tropomyosin off the actin active sitestroponin moves tropomyosin off the actin active sites

1414

Overlap of Thick and Thin FilamentsOverlap of Thick and Thin Filaments

1515

Striations = Organization of FilamentsStriations = Organization of Filaments Dark A bands (regions) alternating with lighter I bands (regions)Dark A bands (regions) alternating with lighter I bands (regions)

anisotrophic (A) and isotropic (I) stand for the way these regions affect polarized anisotrophic (A) and isotropic (I) stand for the way these regions affect polarized lightlight

A band is thick filament regionA band is thick filament region lighter, central H band area lighter, central H band area

contains no thin filamentscontains no thin filaments I band is thin filament regionI band is thin filament region

bisected by Z disc protein called bisected by Z disc protein called connectin, anchoring elastic and thin connectin, anchoring elastic and thin filamentsfilaments

from one Z disc (Z line) to the next is a sarcomerefrom one Z disc (Z line) to the next is a sarcomere

1616

Striations and SarcomeresStriations and Sarcomeres

1717

Relaxed and Contracted SarcomeresRelaxed and Contracted Sarcomeres

Muscle cells shorten because their individual Muscle cells shorten because their individual sarcomeres shorten sarcomeres shorten pulling Z discs closer togetherpulling Z discs closer together pulls on sarcolemmapulls on sarcolemma

Notice neither thick nor thin filaments change Notice neither thick nor thin filaments change length during shorteninglength during shortening

Their overlap changes as sarcomeres shortenTheir overlap changes as sarcomeres shorten

1818

Nerve-Muscle RelationshipsNerve-Muscle Relationships

Skeletal muscle must be stimulated by a Skeletal muscle must be stimulated by a nerve or it will not contractnerve or it will not contract

Cell bodies of somatic motor neurons in Cell bodies of somatic motor neurons in brainstem or spinal cord brainstem or spinal cord

Axons of somatic motor neurons = somatic Axons of somatic motor neurons = somatic motor fibersmotor fibers terminal branches supply one muscle fiberterminal branches supply one muscle fiber

Each motor neuron and all the muscle Each motor neuron and all the muscle fibers it innervates = motor unitfibers it innervates = motor unit

1919

Motor UnitsMotor Units A motor neuron and the muscle fibers it A motor neuron and the muscle fibers it

innervatesinnervates dispersed throughout the muscledispersed throughout the muscle when contract together causes weak when contract together causes weak

contraction over wide areacontraction over wide area provides ability to sustain long-term provides ability to sustain long-term

contraction as motor units take turns resting contraction as motor units take turns resting (postural control)(postural control)

Fine controlFine control small motor units contain as few as small motor units contain as few as

20 muscle fibers per nerve fiber20 muscle fibers per nerve fiber eye muscleseye muscles

Strength controlStrength control gastrocnemius muscle has 1000 gastrocnemius muscle has 1000

fibers per nerve fiberfibers per nerve fiber

2020

Neuromuscular Junctions (Synapse)Neuromuscular Junctions (Synapse)

Functional connection between Functional connection between nerve fiber and muscle cellnerve fiber and muscle cell

Neurotransmitter (acetylcholine/ACh) released from Neurotransmitter (acetylcholine/ACh) released from nerve fiber stimulates muscle cell nerve fiber stimulates muscle cell

Components of synapse (NMJ)Components of synapse (NMJ) synaptic knob is swollen end of nerve fiber (contains ACh)synaptic knob is swollen end of nerve fiber (contains ACh) junctional folds region of sarcolemmajunctional folds region of sarcolemma

• increases surface area for ACh receptorsincreases surface area for ACh receptors• contains acetylcholinesterase that breaks down ACh and causes contains acetylcholinesterase that breaks down ACh and causes

relaxationrelaxation synaptic cleft = tiny gap between nerve and muscle cellssynaptic cleft = tiny gap between nerve and muscle cells Basal lamina = thin layer of collagen and glycoprotein Basal lamina = thin layer of collagen and glycoprotein

over all of muscle fiberover all of muscle fiber

2121

The Neuromuscular JunctionThe Neuromuscular Junction

2222

Neuromuscular ToxinsNeuromuscular Toxins

Pesticides (cholinesterase inhibitors) Pesticides (cholinesterase inhibitors) bind to acetylcholinesterase and prevent it from bind to acetylcholinesterase and prevent it from

degrading AChdegrading ACh spastic paralysis and possible suffocationspastic paralysis and possible suffocation

Tetanus or lockjaw is spastic paralysis Tetanus or lockjaw is spastic paralysis caused by toxin of caused by toxin of ClostridiumClostridium bacteria bacteria blocks glycine release in the spinal cord and blocks glycine release in the spinal cord and

causes overstimulation of the musclescauses overstimulation of the muscles Flaccid paralysis (limp muscles) due to Flaccid paralysis (limp muscles) due to

curare that competes with AChcurare that competes with ACh respiratory arrestrespiratory arrest

2323

Electrically Excitable CellsElectrically Excitable Cells

Plasma membrane is polarized or charged Plasma membrane is polarized or charged resting membrane potential due to Na+ outside of resting membrane potential due to Na+ outside of

cell and K+ and other anions inside of cellcell and K+ and other anions inside of cell difference in charge across the membrane = difference in charge across the membrane =

resting membrane potential (-90 mV cell)resting membrane potential (-90 mV cell) Stimulation opens ion gates in membraneStimulation opens ion gates in membrane

ion gates open (Na+ rushes into cell and K+ ion gates open (Na+ rushes into cell and K+ rushes out of cell)rushes out of cell)• quick up-and-down voltage shift = action potentialquick up-and-down voltage shift = action potential

spreads over cell surface as nerve signalspreads over cell surface as nerve signal

2424

Muscle Contraction and RelaxationMuscle Contraction and Relaxation

Four actions involved in this processFour actions involved in this process excitation = nerve action potentials lead to excitation = nerve action potentials lead to

action potentials in muscle fiberaction potentials in muscle fiber excitation-contraction coupling = action excitation-contraction coupling = action

potentials on the sarcolemma activate potentials on the sarcolemma activate myofilamentsmyofilaments

contraction = shortening of muscle fiber contraction = shortening of muscle fiber relaxation = return to resting lengthrelaxation = return to resting length

Images will be used to demonstrate the Images will be used to demonstrate the steps of each of these actionssteps of each of these actions

2525

Excitation of a Muscle FiberExcitation of a Muscle Fiber

2626

Excitation (steps 1 and 2)Excitation (steps 1 and 2)

Nerve signal opens voltage-gated calcium channels. Calcium Nerve signal opens voltage-gated calcium channels. Calcium stimulates exocytosis of synaptic vesicles containing ACh = stimulates exocytosis of synaptic vesicles containing ACh = ACh release into synaptic cleft.ACh release into synaptic cleft.

2727

Excitation (steps 3 and 4)Excitation (steps 3 and 4)

Binding of ACh to receptor proteins opens Na+ and K+ channels resulting in jump in RMP from -90mV to +75mV forming an end-plate potential (EPP).

2828

Excitation (step 5)Excitation (step 5)

Voltage change in end-plate region (EPP) opens nearby voltage-gated channels producing an action potential

2929

Excitation-Contraction CouplingExcitation-Contraction Coupling

3030

Excitation-Contraction Coupling (steps 6 and 7)Excitation-Contraction Coupling (steps 6 and 7)

Action potential spreading over sarcolemma enters T Action potential spreading over sarcolemma enters T tubules -- voltage-gated channels open in T tubules tubules -- voltage-gated channels open in T tubules causing calcium gates to open in SRcausing calcium gates to open in SR

3131

Excitation-Contraction Coupling (steps 8 and 9)Excitation-Contraction Coupling (steps 8 and 9)

Calcium released by SR binds to troponinCalcium released by SR binds to troponin Troponin-tropomyosin complex changes shape Troponin-tropomyosin complex changes shape

and exposes active sites on actinand exposes active sites on actin

3232

Contraction (steps 10 and 11)Contraction (steps 10 and 11)

Myosin ATPase in myosin head hydrolyzes an ATP Myosin ATPase in myosin head hydrolyzes an ATP molecule, activating the head and “cocking” it in an molecule, activating the head and “cocking” it in an extended positionextended position

It binds to actin active site forming a cross-bridgeIt binds to actin active site forming a cross-bridge

3333

Contraction Contraction (steps 12 and 13)(steps 12 and 13) Power stroke = Power stroke =

myosin head releasesmyosin head releasesADP and phosphate as ADP and phosphate as it flexes pulling the thin it flexes pulling the thin filament past the thickfilament past the thick

With the binding of more With the binding of more ATP, the myosin head ATP, the myosin head extends to attach to a extends to attach to a new active sitenew active site half of the heads are bound to a thin filament at half of the heads are bound to a thin filament at

one time preventing slippageone time preventing slippage thin and thick filaments do not become shorter, thin and thick filaments do not become shorter,

just slide past each other (sliding filament just slide past each other (sliding filament theory)theory)

3434

Relaxation Relaxation (steps 14 and 15)(steps 14 and 15)

Nerve stimulation ceases and acetylcholinesterase Nerve stimulation ceases and acetylcholinesterase removes ACh from receptors. Stimulation of the muscle removes ACh from receptors. Stimulation of the muscle cell ceases.cell ceases.

3535

Relaxation Relaxation (step 16)(step 16)

Active transport needed to pump calcium back Active transport needed to pump calcium back into SR to bind to calsequestrininto SR to bind to calsequestrin

ATP is needed for muscle relaxation as well as ATP is needed for muscle relaxation as well as muscle contractionmuscle contraction

3636

Relaxation Relaxation (steps 17 and 18)(steps 17 and 18)

Loss of calcium from sarcoplasm moves troponin-Loss of calcium from sarcoplasm moves troponin-tropomyosin complex over active sitestropomyosin complex over active sites stops the production or maintenance of tensionstops the production or maintenance of tension

Muscle fiber returns to its resting length due to recoil Muscle fiber returns to its resting length due to recoil of series-elastic components and contraction of of series-elastic components and contraction of antagonistic musclesantagonistic muscles

3737

Rigor MortisRigor Mortis

Stiffening of the body beginning 3 to 4 hours after Stiffening of the body beginning 3 to 4 hours after death death

Deteriorating sarcoplasmic reticulum releases Deteriorating sarcoplasmic reticulum releases calciumcalcium

Calcium activates myosin-actin cross-bridging and Calcium activates myosin-actin cross-bridging and muscle contracts, but can not relax.muscle contracts, but can not relax.

Muscle relaxation requires ATP and ATP production Muscle relaxation requires ATP and ATP production is no longer produced after deathis no longer produced after death

Fibers remain contracted until myofilaments decayFibers remain contracted until myofilaments decay

3838

Length-Tension RelationshipLength-Tension Relationship Amount of tension generated depends on length of Amount of tension generated depends on length of

muscle before it was stimulatedmuscle before it was stimulated length-tension relationship (see graph next slide)length-tension relationship (see graph next slide)

Overly contracted (weak contraction results)Overly contracted (weak contraction results) thick filaments too close to Z discs and can’t slidethick filaments too close to Z discs and can’t slide

Too stretched (weak contraction results)Too stretched (weak contraction results) little overlap of thin and thick does not allow for very many little overlap of thin and thick does not allow for very many

cross bridges too formcross bridges too form

Optimum resting length produces greatest force Optimum resting length produces greatest force when muscle contractswhen muscle contracts central nervous system maintains optimal length central nervous system maintains optimal length

producing muscle tone or partial contraction producing muscle tone or partial contraction

3939

Length-Tension CurveLength-Tension Curve

4040

Muscle Twitch in FrogMuscle Twitch in Frog

Threshold = voltage producing an Threshold = voltage producing an action potentialaction potential a single brief stimulus at that voltage a single brief stimulus at that voltage

produces a quick cycle of contraction produces a quick cycle of contraction and relaxation called a twitch (lasting and relaxation called a twitch (lasting less than 1/10 second)less than 1/10 second)

A single twitch contraction is not A single twitch contraction is not strong enough to do any useful strong enough to do any useful workwork

4141

Muscle Twitch in Frog 2Muscle Twitch in Frog 2

Phases of a twitch contractionPhases of a twitch contraction latent period (2 msec delay)latent period (2 msec delay)

• only internal tension is generatedonly internal tension is generated• no visible contraction occurs since no visible contraction occurs since

only elastic components are being only elastic components are being stretchedstretched

contraction phasecontraction phase• external tension develops as muscle external tension develops as muscle

shortensshortens relaxation phase relaxation phase

• loss of tension and return loss of tension and return to resting length as calcium returns to SRto resting length as calcium returns to SR

4242

Contraction Strength of TwitchesContraction Strength of Twitches

Threshold stimuli produces twitchesThreshold stimuli produces twitches Twitches unchanged despite increased voltageTwitches unchanged despite increased voltage ““Muscle fiber obeys an all-or-none law” Muscle fiber obeys an all-or-none law”

contracting to its maximum or not at allcontracting to its maximum or not at all not a true statement since twitches vary in strengthnot a true statement since twitches vary in strength

• depending upon, Ca2+ concentration, previous stretch of the depending upon, Ca2+ concentration, previous stretch of the muscle, temperature, pH and hydrationmuscle, temperature, pH and hydration

Closer stimuli produce stronger twitchesCloser stimuli produce stronger twitches

4343

Recruitment and Stimulus IntensityRecruitment and Stimulus Intensity

Stimulating the whole nerve with higher and higher Stimulating the whole nerve with higher and higher voltage produces stronger contractionsvoltage produces stronger contractions

More motor units are being recruitedMore motor units are being recruited called multiple motor unit summationcalled multiple motor unit summation lift a glass of milk versus a whole gallon of milklift a glass of milk versus a whole gallon of milk

4444

Twitch and Treppe ContractionsTwitch and Treppe Contractions

Muscle stimulation at variable frequenciesMuscle stimulation at variable frequencies low frequency (up to 10 stimuli/sec)low frequency (up to 10 stimuli/sec)

• each stimulus produces an identical twitch responseeach stimulus produces an identical twitch response moderate frequency (between 10-20 stimuli/sec)moderate frequency (between 10-20 stimuli/sec)

• each twitch has time to recover but develops more tension each twitch has time to recover but develops more tension than the one before (treppe phenomenon)than the one before (treppe phenomenon)

calcium was not completely put back into SRcalcium was not completely put back into SR heat of tissue increases myosin ATPase efficiency heat of tissue increases myosin ATPase efficiency

4545

Incomplete and Complete TetanusIncomplete and Complete Tetanus

Higher frequency stimulation (20-40 stimuli/second) Higher frequency stimulation (20-40 stimuli/second) generates gradually more strength of contractiongenerates gradually more strength of contraction

each stimuli arrives before last one recoverseach stimuli arrives before last one recovers• temporal summation or wave summationtemporal summation or wave summation

incomplete tetanus = sustained fluttering contractionsincomplete tetanus = sustained fluttering contractions

Maximum frequency stimulation (40-50 stimuli/second)Maximum frequency stimulation (40-50 stimuli/second) muscle has no time to relax at allmuscle has no time to relax at all twitches fuse into smooth, prolonged contraction called complete twitches fuse into smooth, prolonged contraction called complete

tetanustetanus rarely occurs in the bodyrarely occurs in the body

4646

Isometric and Isotonic ContractionsIsometric and Isotonic Contractions

Isometric muscle contractionIsometric muscle contraction develops tension without changing lengthdevelops tension without changing length important in postural muscle function and antagonistic important in postural muscle function and antagonistic

muscle joint stabilizationmuscle joint stabilization Isotonic muscle contractionIsotonic muscle contraction

tension while shortening = concentrictension while shortening = concentric tension while lengthening = eccentrictension while lengthening = eccentric

4747

Muscle Contraction PhasesMuscle Contraction Phases

Isometric and isotonic phases of lifting Isometric and isotonic phases of lifting tension builds though the box is not movingtension builds though the box is not moving muscle begins to shortenmuscle begins to shorten tension maintained tension maintained

4848

ATP SourcesATP Sources

All muscle contraction depends on ATPAll muscle contraction depends on ATP Pathways of ATP synthesisPathways of ATP synthesis

anaerobic fermentation (ATP production limited)anaerobic fermentation (ATP production limited)• without oxygen, produces toxic lactic acidwithout oxygen, produces toxic lactic acid

aerobic respiration (more ATP produced)aerobic respiration (more ATP produced)• requires continuous oxygen supply, produces H2O and CO2requires continuous oxygen supply, produces H2O and CO2

4949

Immediate Energy NeedsImmediate Energy Needs

Short, intense exercise (100 m Short, intense exercise (100 m dash)dash)

oxygen need is supplied by oxygen need is supplied by myoglobinmyoglobin

Phosphagen systemPhosphagen system myokinase transfers Pmyokinase transfers Pii groups groups

from one ADP to another forming from one ADP to another forming ATPATP

creatine kinase transfers Pi creatine kinase transfers Pi groups from creatine phosphate groups from creatine phosphate to make ATPto make ATP

Result is power enough for 1 Result is power enough for 1 minute brisk walk or 6 seconds minute brisk walk or 6 seconds of sprinting of sprinting

5050

Short-Term Energy NeedsShort-Term Energy Needs

Glycogen-lactic acid system takes overGlycogen-lactic acid system takes over produces ATP for 30-40 seconds of produces ATP for 30-40 seconds of

maximum activitymaximum activity• playing basketball or running around baseball playing basketball or running around baseball

diamonds diamonds muscles obtain glucose from blood and stored muscles obtain glucose from blood and stored

glycogenglycogen

5151

Long-Term Energy NeedsLong-Term Energy Needs

Aerobic respiration needed for prolonged Aerobic respiration needed for prolonged exerciseexercise Produces 36 ATPs/glucose moleculeProduces 36 ATPs/glucose molecule

After 40 seconds of exercise, respiratory and After 40 seconds of exercise, respiratory and cardiovascular systems must deliver enough cardiovascular systems must deliver enough oxygen for aerobic respirationoxygen for aerobic respiration oxygen consumption rate increases for first 3-4 oxygen consumption rate increases for first 3-4

minutes and then levels off to a steady stateminutes and then levels off to a steady state

Limits are set by depletion of glycogen and Limits are set by depletion of glycogen and blood glucose, loss of fluid and electrolytesblood glucose, loss of fluid and electrolytes

5252

FatigueFatigue

Progressive weakness from useProgressive weakness from use ATP synthesis declines as glycogen is ATP synthesis declines as glycogen is

consumedconsumed sodium-potassium pumps fail to maintain sodium-potassium pumps fail to maintain

membrane potential and excitabilitymembrane potential and excitability lactic acid inhibits enzyme functionlactic acid inhibits enzyme function accumulation of extracellular K+ hyperpolarizes accumulation of extracellular K+ hyperpolarizes

the cellthe cell motor nerve fibers use up their acetylcholinemotor nerve fibers use up their acetylcholine

5353

EnduranceEndurance

Ability to maintain high-intensity exercise for Ability to maintain high-intensity exercise for >5 minutes>5 minutes determined by maximum oxygen uptakedetermined by maximum oxygen uptake

• VOVO22 max is proportional to body size, peaks at age max is proportional to body size, peaks at age

20, is larger in trained athlete and males20, is larger in trained athlete and males nutrient availabilitynutrient availability

• carbohydrate loading used by some athletescarbohydrate loading used by some athletes packs glycogen into muscle cellspacks glycogen into muscle cells adds water at same time (2.7 g water with each adds water at same time (2.7 g water with each

gram/glycogen)gram/glycogen)• side effects include “heaviness” feelingside effects include “heaviness” feeling

5454

Oxygen DebtOxygen Debt Heavy breathing after strenuous exerciseHeavy breathing after strenuous exercise

known as excess postexercise oxygen consumption known as excess postexercise oxygen consumption (EPOC)(EPOC)

typically about 11 liters extra is consumedtypically about 11 liters extra is consumed Purposes for extra oxygenPurposes for extra oxygen

replace oxygen reserves (myoglobin, blood replace oxygen reserves (myoglobin, blood hemoglobin, in air in the lungs and dissolved in hemoglobin, in air in the lungs and dissolved in plasma)plasma)

replenishing the phosphagen systemreplenishing the phosphagen system reconverting lactic acid to glucose in kidneys and liverreconverting lactic acid to glucose in kidneys and liver serving the elevated metabolic rate that occurs as serving the elevated metabolic rate that occurs as

long as the body temperature remains elevated by long as the body temperature remains elevated by exerciseexercise

5555

Slow- and Fast-Twitch FibersSlow- and Fast-Twitch Fibers

Slow oxidative, slow-twitch fibersSlow oxidative, slow-twitch fibers more mitochondria, myoglobin and more mitochondria, myoglobin and

capillariescapillaries adapted for aerobic respiration and adapted for aerobic respiration and

resistant to fatigueresistant to fatigue soleus and postural muscles of the back soleus and postural muscles of the back

(100msec/twitch)(100msec/twitch)

5656

Slow and Fast-Twitch FibersSlow and Fast-Twitch Fibers

Fast glycolytic, fast-twitch fibersFast glycolytic, fast-twitch fibers rich in enzymes for phosphagen and rich in enzymes for phosphagen and

glycogen-lactic acid systemsglycogen-lactic acid systems sarcoplasmic reticulum releases calcium sarcoplasmic reticulum releases calcium

quickly so contractions are quicker (7.5 quickly so contractions are quicker (7.5 msec/twitch)msec/twitch)

extraocular eye muscles, gastrocnemius and extraocular eye muscles, gastrocnemius and biceps brachiibiceps brachii

Proportions genetically determined Proportions genetically determined

5757

Strength and ConditioningStrength and Conditioning

Strength of contractionStrength of contraction muscle size and fascicle arrangementmuscle size and fascicle arrangement

• 3 or 4 kg / cm2 of cross-sectional area3 or 4 kg / cm2 of cross-sectional area size of motor units and motor unit recruitmentsize of motor units and motor unit recruitment length of muscle at start of contraction length of muscle at start of contraction

Resistance training (weight lifting)Resistance training (weight lifting) stimulates cell enlargement due to synthesis of more stimulates cell enlargement due to synthesis of more

myofilamentsmyofilaments

Endurance training (aerobic exercise)Endurance training (aerobic exercise) produces an increase in mitochondria, glycogen and produces an increase in mitochondria, glycogen and

density of capillariesdensity of capillaries

5858

Cardiac Muscle 1Cardiac Muscle 1

Thick cells shaped like a log with uneven, notched Thick cells shaped like a log with uneven, notched endsends

Linked to each other at intercalated discsLinked to each other at intercalated discs electrical gap junctions allow cells to stimulate their electrical gap junctions allow cells to stimulate their

neighborsneighbors mechanical junctions keep the cells from pulling apartmechanical junctions keep the cells from pulling apart

Sarcoplasmic reticulum less developed but large T Sarcoplasmic reticulum less developed but large T tubules admit Ca+2 from extracellular fluidtubules admit Ca+2 from extracellular fluid

Damaged cells repaired by fibrosis, not mitosisDamaged cells repaired by fibrosis, not mitosis

5959

Cardiac Muscle 2Cardiac Muscle 2

Autorhythmic due to pacemaker cellsAutorhythmic due to pacemaker cells Uses aerobic respiration almost Uses aerobic respiration almost

exclusivelyexclusively large mitochondria make it resistant to fatiguelarge mitochondria make it resistant to fatigue very vulnerable to interruptions in oxygen very vulnerable to interruptions in oxygen

supplysupply

6060

Smooth MuscleSmooth Muscle Fusiform cells with one nucleusFusiform cells with one nucleus

30 to 200 microns long and 5 to 10 microns wide30 to 200 microns long and 5 to 10 microns wide no striations, sarcomeres or Z discsno striations, sarcomeres or Z discs thin filaments attach to dense bodies scattered thin filaments attach to dense bodies scattered

throughout sarcoplasm and on sarcolemmathroughout sarcoplasm and on sarcolemma SR is scanty and has no T tubulesSR is scanty and has no T tubules

• calcium for contraction comes from extracellular fluidcalcium for contraction comes from extracellular fluid

If present, nerve supply is autonomicIf present, nerve supply is autonomic releases either ACh or norepinephrinereleases either ACh or norepinephrine

6161

Types of Smooth MuscleTypes of Smooth Muscle

Multiunit smooth muscleMultiunit smooth muscle largest arteries, iris, pulmonary air passages, largest arteries, iris, pulmonary air passages,

arrector pili musclesarrector pili muscles terminal nerve branches synapse on terminal nerve branches synapse on

myocytesmyocytes independent contractionindependent contraction

6262

Types of Smooth MuscleTypes of Smooth Muscle

Single-unit smooth muscleSingle-unit smooth muscle most blood vessels and viscera as circular most blood vessels and viscera as circular

and longitudinal muscle layersand longitudinal muscle layers electrically coupled by gap junctionselectrically coupled by gap junctions large number of cells contract as a unitlarge number of cells contract as a unit

6363

Stimulation of Smooth MuscleStimulation of Smooth Muscle

6464

Stimulation of Smooth MuscleStimulation of Smooth Muscle

Involuntary and contracts without nerve Involuntary and contracts without nerve stimulationstimulation hormones, CO2, low pH, stretch, O2 deficiencyhormones, CO2, low pH, stretch, O2 deficiency pacemaker cells in GI tract are autorhythmicpacemaker cells in GI tract are autorhythmic

Autonomic nerve fibers have beadlike Autonomic nerve fibers have beadlike swellings called varicosities containing swellings called varicosities containing synaptic vesiclessynaptic vesicles stimulates multiple myocytes at diffuse junctionsstimulates multiple myocytes at diffuse junctions

6565

Features of Contraction and RelaxationFeatures of Contraction and Relaxation

Calcium triggering contraction is extracellularCalcium triggering contraction is extracellular calcium channels triggered to open by voltage, calcium channels triggered to open by voltage,

hormones, neurotransmitters or cell stretchinghormones, neurotransmitters or cell stretching• calcium ions bind to calmodulincalcium ions bind to calmodulin• activates light-chain myokinase which activates myosin ATPase activates light-chain myokinase which activates myosin ATPase • power stroke occurs when ATP hydrolyzedpower stroke occurs when ATP hydrolyzed

Thin filaments pull on intermediate filaments Thin filaments pull on intermediate filaments attached to dense bodies on the plasma attached to dense bodies on the plasma membranemembrane shortens the entire cell in a twisting fashionshortens the entire cell in a twisting fashion

6666

Contraction and relaxation very slow in Contraction and relaxation very slow in comparisoncomparison slow myosin ATPase enzyme and slow slow myosin ATPase enzyme and slow

pumps that remove Ca+2pumps that remove Ca+2 Uses 10-300 times less ATP to maintain Uses 10-300 times less ATP to maintain

the same tensionthe same tension latch-bridge mechanism maintains tetanus latch-bridge mechanism maintains tetanus

(muscle tone)(muscle tone)• keeps arteries in state of partial contraction keeps arteries in state of partial contraction

(vasomotor tone)(vasomotor tone)

Features of Contraction and RelaxationFeatures of Contraction and Relaxation

6767

Contraction of Smooth MuscleContraction of Smooth Muscle

6868

Responses to Stretch 1Responses to Stretch 1

Stretch opens mechanically-gated calcium Stretch opens mechanically-gated calcium channels causing muscle responsechannels causing muscle response food entering the esophagus brings on peristalsisfood entering the esophagus brings on peristalsis

Stress-relaxation response necessary for Stress-relaxation response necessary for hollow organs that gradually fill (urinary hollow organs that gradually fill (urinary bladder)bladder) when stretched, tissue briefly contracts then when stretched, tissue briefly contracts then

relaxesrelaxes

6969

Must contract forcefully when greatly Must contract forcefully when greatly stretchedstretched thick filaments have heads along their entire thick filaments have heads along their entire

lengthlength no orderly filament arrangement -- no Z discsno orderly filament arrangement -- no Z discs

Plasticity is ability to adjust tension to Plasticity is ability to adjust tension to degree of stretch such as empty bladder is degree of stretch such as empty bladder is not flabbynot flabby

Responses to Stretch 2Responses to Stretch 2

7070

Muscular DystrophyMuscular Dystrophy Hereditary diseases - skeletal muscles Hereditary diseases - skeletal muscles

degenerate and are replaced with adiposedegenerate and are replaced with adipose Disease of malesDisease of males

appears as child begins to walkappears as child begins to walk rarely live past 20 years of agerarely live past 20 years of age

Dystrophin links actin filaments to cell Dystrophin links actin filaments to cell membranemembrane leads to torn cell membranes and necrosisleads to torn cell membranes and necrosis

Fascioscapulohumeral MD -- facial and Fascioscapulohumeral MD -- facial and shoulder muscle onlyshoulder muscle only

7171

Myasthenia GravisMyasthenia Gravis Autoimmune disease - antibodies attack Autoimmune disease - antibodies attack

NMJ and bind ACh receptors in clustersNMJ and bind ACh receptors in clusters receptors removedreceptors removed less and less sensitive to AChless and less sensitive to ACh

• drooping eyelids and double vision, difficulty drooping eyelids and double vision, difficulty swallowing, weakness of the limbs, respiratory failureswallowing, weakness of the limbs, respiratory failure

Disease of women between 20 and 40Disease of women between 20 and 40 Treated with cholinesterase inhibitors, Treated with cholinesterase inhibitors,

thymus removal or immunosuppressive thymus removal or immunosuppressive agentsagents

7272

Myasthenia GravisMyasthenia Gravis

Drooping eyelids and weakness of muscles of eye movement