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Structure and Function of
Skeletal Muscle
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Skeletal MuscleHuman body contains over 400skeletal muscles
40-50% of total body weightFunctions of skeletal muscle
Force roduction for locomotion and
breathingForce roduction for ostural su ortHeat roduction during cold stress
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Structure of SkeletalMuscle!Connective Tissue
Covering
" imysiumSurrounds entire muscle
#erimysiumSurrounds bundles of muscle $bers
Fascicles
"ndomysiumSurrounds individual muscle $bers
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Structure of SkeletalMuscle!MicrostructureSarcolemma
Muscle cell membrane
Myo$brils hreadlike strands within muscle $bers&ctin 'thin $lament(
ro onin ro omyosin
Myosin 'thick $lament(
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Structure of SkeletalMuscle!The SarcomereFurther divisions of myo$brils
)-line
&-band*-band
+ithin the sarco lasmSarco lasmic reticulum
Storage sites for calcium
ransverse tubules erminal cisternae
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he ,euromuscular unction
Site where motor neuron meets the muscle$ber
Se arated by ga called the neuromuscular cleftMotor end late
#ocket formed around motor neuron bysarcolemma
&cetylcholine is released from the motorneuron
.auses an end- late otential '"##(/e olari ation of muscle $ber
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*llustration of the,euromuscular unction
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Motor 1nitSingle motorneuron 2 muscle$bers it innervates"ye muscles 3 ! muscle nerveratioHamstrings 3 600! muscle nerveratio
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Muscular .ontraction he sliding $lament model
Muscle shortening occurs due to themovement of the actin $lament overthe myosin $lamentFormation of cross-bridges between
actin and myosin $laments7eduction in the distance between )-lines of the sarcomere
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he Sliding Filament Modelof Muscle .ontraction
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.ross-8ridge Formation inMuscle .ontraction
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Sliding Filament heory7est 3 uncharged & # cross-bridgecom le9
"9citation-cou ling 3 charged & # cross-bridge com le9: ;turned on<.ontraction 3 actomyosin 3 & # = &/# 2#i > energy7echarging 3 reload cross-bridge with & #7ela9ation 3 cross-bridges ;turned o?<
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Muscle Function&ll or none law 3 $ber contractscom letely or not at allMuscle strength gradation
Multi le motor unit summation 3 moremotor units er unit of time
+ave summation 3 vary fre@uency ofcontraction of individual motor units
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"nergy for Muscle.ontraction
& # is re@uired for musclecontraction
Myosin & #ase breaks down & # as$ber contracts
Sources of & #
#hos hocreatine '#.(AlycolysisB9idative hos horylation
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Sources of & # for Muscle.ontraction
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#ro erties of Muscle Fibers8iochemical ro erties
B9idative ca acity y e of & #ase
.ontractile ro ertiesMa9imal force roductionS eed of contractionMuscle $ber eCciency
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*ndividual Fiber y esFast $bers
y e **b $bers
Fast-twitch $bersFast-glycolytic$bers
y e **a $bers*ntermediate $bersFast-o9idativeglycolytic $bers
Slow $bers y e * $bers
Slow-twitch $bersSlow-o9idative$bers
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.om arison of Ma9imalShortening Delocities8etween Fiber y es
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Histochemical Staining ofFiber y e
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Fiber y es and#erformance
#ower athletesS rinters
#ossess high ercentage of fast $bers"ndurance athletes/istance runnersHave high ercentage of slow $bers
Bthers+eight lifters and nonathletesHave about 50% slow and 50% fast $bers
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raining-*nduced .hangesin Muscle Fiber y e
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Hy ertro hy andHy er lasia
*ncrease in si e *ncrease innumber
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&ge-7elated .hanges inSkeletal Muscle
&ging is associated with a loss ofmuscle mass
7ate increases after 50 years of age7egular e9ercise training canim rove strength and endurance
.annot com letely eliminate the age-related loss in muscle mass
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y es of Muscle
.ontraction*sometric
Muscle e9erts force without changing length
#ulling against immovable obEect#ostural muscles
*sotonic 'dynamic(.oncentric
Muscle shortens during force roduction
"ccentricMuscle roduces force but length increases
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*sotonic and *sometric
.ontractions
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*llustration of a Sim le
witch
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Force 7egulation in Muscle y es and number of motor units recruited
More motor units greater force
Fast motor units greater force*nitial muscle length
;*deal< length for force generation
,ature of the motor units neural
stimulationFre@uency of stimulation
Sim le twitch: summation: and tetanus
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7elationshi 8etween
Stimulus Fre@uency andForce Aeneration
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Gength- ension
7elationshi in SkeletalMuscle
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Force-Delocity 7elationshi&t any absolute force the s eed ofmovement is greater in muscle with
higher ercent of fast-twitch $bers he ma9imum velocity of shorteningis greatest at the lowest force
rue for both slow and fast-twitch $bers
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Force-Delocity 7elationshi
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Force-#ower 7elationshi&t any given velocity of movementthe ower generated is greater in a
muscle with a higher ercent offast-twitch $bers he eak ower increases withvelocity u to movement s eed of
00-600 degreesIsecond -Force decreases with increasingmovement s eed beyond this velocity
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Force-#ower 7elationshi
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7ece tors in MuscleMuscle s indle
/etect dynamic and static changes inmuscle lengthStretch reJe9
Stretch on muscle causes reJe9 contraction
Aolgi tendon organ 'A B(Monitor tension develo ed in muscle#revents damage during e9cessive forcegeneration
Stimulation results in reJe9 rela9ation of muscle
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Muscle S indle
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Aolgi endon Brgan
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