MUSCLE and MUSCLE TISSUE

transcript

MUSCLE MUSCLE and and

MUSCLE TISSUEMUSCLE TISSUE

Chapter 11Chapter 11

Muscles are Muscles are distinguished by distinguished by their ability to their ability to turn ATP turn ATP (chemical (chemical energy) into work energy) into work (mechanical (mechanical energy)energy)

Muscles do Muscles do their work in their work in one way – they one way – they contractcontract

myomyo – (Greek) – (Greek) “muscle”“muscle”

SarcoSarco – (Greek) – (Greek) “flesh”“flesh”

Muscle TypesMuscle TypesSkeletalSkeletal

Attached to and Attached to and covers bonescovers bones

StriationsStriations““voluntary”voluntary”Powerful but Powerful but

tire easilytire easily

CardiacCardiacIsolated; found only Isolated; found only

in heartin heartStriatedStriated““involuntary”involuntary”Contraction is Contraction is

regular and regular and controlled by neural controlled by neural transmissiontransmission

VisceralVisceral““Smooth”Smooth”InvoluntaryInvoluntaryNo striatonsNo striatonsContraction is Contraction is slow and slow and sustainedsustained

FunctionsFunctionsMovementMovement

Locomotion and manipulation Locomotion and manipulation by skeletal muscleby skeletal muscle

Blood coursing – cardiac Blood coursing – cardiac musclemuscle

Propulsion and/or squeezing Propulsion and/or squeezing of substances – smooth of substances – smooth musclemuscle

Posture MaintenancePosture MaintenanceSkeletal muscleSkeletal muscleCounteracts gravityCounteracts gravity

Heat GenerationHeat GenerationBy-product of muscle By-product of muscle metabolism and contractile metabolism and contractile activityactivity

Skeletal muscle (40% of Skeletal muscle (40% of body mass) is responsiblebody mass) is responsible

PropertiesPropertiesExcitabilityExcitability – ability to receive and – ability to receive and

respond to a stimulus (usually a respond to a stimulus (usually a neurotransmitter)neurotransmitter)

ContractilityContractility – ability to shorten – ability to shorten when stimulatedwhen stimulated

ExtensibilityExtensibility – ability to be – ability to be stretched or extended – to a pointstretched or extended – to a point

ElasticityElasticity – resumes its resting – resumes its resting lengthlength

Skeletal Muscle – Gross AnatomySkeletal Muscle – Gross Anatomy

EpimysiumEpimysium – connective tissue – connective tissue covering entire muscle covering entire muscle structure structure

FascicleFascicle – bound and separated – bound and separated by by perimysiumperimysium

Muscle fibersMuscle fibers – bound and – bound and separated by separated by endomysiumendomysium

Myofibrils- Myofibrils- composed of composed of myofilamentsmyofilaments

Myofilaments Myofilaments - composed of actin - composed of actin and myosin protein fibersand myosin protein fibers

Connective tissue sheaths provide Connective tissue sheaths provide strength to the fragile muscle strength to the fragile muscle fibers; allow a route of entry and fibers; allow a route of entry and exit for blood and nerve fibersexit for blood and nerve fibers

MetabolicMetabolic SupplySupplyNerve endingsNerve endingsVascularityVascularity

Muscle AttachmentMuscle AttachmentDirect attachmentDirect attachment: :

epimysium to periosteum of epimysium to periosteum of bone.bone.

Indirect attachmentIndirect attachment: : epimysium forms a tendon to epimysium forms a tendon to epimysium of another muscle epimysium of another muscle or periosteum of bone. or periosteum of bone.

Fascicle ArrangementFascicle ArrangementPattern influences range of motion Pattern influences range of motion

and powerand powerLong fibers = more range of motionLong fibers = more range of motionPower related to number of muscle Power related to number of muscle

fibersfibersSee page 244 of textSee page 244 of text

Microscopic Anatomy of Skeletal Microscopic Anatomy of Skeletal MuscleMuscle

Typically cylindrical, long, Typically cylindrical, long, multinucleatedmultinucleated

SarcolemmaSarcolemma (cell (cell membrane) – membrane) – forms elongated forms elongated tubes deep into tubes deep into the cell interior – the cell interior – “T tubules” “T tubules”

SarcoplasmSarcoplasm – with – with stored glycogen stored glycogen and myoglobinand myoglobin

Sarcoplasmic Sarcoplasmic ReticulumReticulumSpecialized smooth E.R.Specialized smooth E.R.Connected to Connected to sarcolemmasarcolemma

(plasma membrane); (plasma membrane); provides passage for provides passage for neurotransmitter, glucose, neurotransmitter, glucose, oxygen, etc. into fiberoxygen, etc. into fiber

Regulates intracellular levels Regulates intracellular levels of Ca+ (holds and releases of Ca+ (holds and releases Ca+ on demand)Ca+ on demand)

SarcomeresSarcomeres – smallest contractile – smallest contractile unit of muscle fiber; made of myofibrilsunit of muscle fiber; made of myofibrils

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MyofibrilsMyofibrils – 80% of cell volume; – 80% of cell volume; contractile element of cellcontractile element of cellAlternating bands of dark and Alternating bands of dark and

light along length; give myofibril light along length; give myofibril “striated” appearance“striated” appearance

Banding due to 2 distinct protein Banding due to 2 distinct protein filaments (“filaments (“myofilamentsmyofilaments”) within ”) within sarcomeresarcomere

Myofilaments

Thick filaments – composed Thick filaments – composed of of myosinmyosin protein proteinTail with 2 heads at one end Tail with 2 heads at one end – “cross bridges”– “cross bridges”

Heads contain ATPasesHeads contain ATPasesTails bundled together with Tails bundled together with heads studded outwardheads studded outward

Thin filaments – Thin filaments – composed of composed of actinactin protein protein Strands of protein coil Strands of protein coil around each other to around each other to give appearance of give appearance of twisted pearl necklacetwisted pearl necklace

Sliding Filament TheorySliding Filament TheoryThin filaments slide past thick Thin filaments slide past thick

filaments causing a myofibril filaments causing a myofibril overlapoverlap

During contraction, thin During contraction, thin filaments penetrate deeperfilaments penetrate deeper

Causes slidingCauses sliding

Physiology of Muscle ContractionPhysiology of Muscle ContractionRequires ACh & Ca+Requires ACh & Ca+Stimulation by neurotransmitterStimulation by neurotransmitterACh receptors on sarcolemma ACh receptors on sarcolemma

cause Na+ to flood muscle cellcause Na+ to flood muscle cellNa+ causes sarcoplasmic Na+ causes sarcoplasmic

reticulum to release Ca+reticulum to release Ca+Ca+ binds to Ca+ binds to actinactin = exposing = exposing

actin/myosin binding sitesactin/myosin binding sites

Myosin heads bind to Myosin heads bind to exposed actin heads exposed actin heads (exposed in presence of (exposed in presence of Ca+ which moves Ca+ which moves molecules covering actin molecules covering actin binding sites)binding sites)

Myosin head binds, forming Myosin head binds, forming cross bridgescross bridges, using energy , using energy from previous ATP from previous ATP hydrolysishydrolysis

Myosin head releases ADP Myosin head releases ADP (energy), thereby pulling (energy), thereby pulling myofilaments = “power myofilaments = “power stroke” stroke”

Ca+ is reabsorbed, myosin cross Ca+ is reabsorbed, myosin cross bridges are broken, muscle bridges are broken, muscle relaxes.relaxes.

???What causes rigor mortis??????What causes rigor mortis???

Muscle Contraction – Gross LevelMuscle Contraction – Gross LevelMuscles respond in an “all-or-none” Muscles respond in an “all-or-none”

fashionfashion150 muscle fibers/motor nerve, one 150 muscle fibers/motor nerve, one

neuron + all the fibers it innervates = neuron + all the fibers it innervates = one motor unitone motor unit

Fibers within a motor unit are Fibers within a motor unit are scattered throughout scattered throughout

Muscles requiring fine motor Muscles requiring fine motor control have fibers of one nerve control have fibers of one nerve close together - fingersclose together - fingers

Muscle MechanicsMuscle MechanicsWave Wave

summation – summation – recruit more recruit more cellscells

Tetanus – Tetanus – sustained sustained contractioncontraction

Series of twitches

Summation

Tetanic contraction

Isotonic – muscle length variesIsotonic – muscle length variesIsometric – muscle length stays Isometric – muscle length stays

the samethe sameMuscle tone – slight contraction at Muscle tone – slight contraction at

restrest

Muscle MetabolismMuscle MetabolismWhen ATP synthesis < ATP use then one When ATP synthesis < ATP use then one

of several things happens because of several things happens because muscles store very little ATP:muscles store very little ATP:ADP + creatine phosphateADP + creatine phosphateAerobic respirationAerobic respirationAnaerobic respirationAnaerobic respiration

Muscle fatigueMuscle fatigueContractures – permanent shorteningContractures – permanent shorteningOxygen debt – lactic acid buildupOxygen debt – lactic acid buildup

Animation:Animation:Energy Sources for Energy Sources for Prolonged ExerciseProlonged Exercise

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Force, Velocity, & Duration of Force, Velocity, & Duration of ContractionContraction

ForceForceVelocity and duration – dependent Velocity and duration – dependent

upon fiber typesupon fiber typesSlow twitch, fatigue resistantSlow twitch, fatigue resistantFast twitch, fatigue vulnerableFast twitch, fatigue vulnerableFast twitch, fatigue resistantFast twitch, fatigue resistant

Most muscles are a mixture; some Most muscles are a mixture; some areas of body specializeareas of body specialize

Slow Twitch Muscle FibersSlow Twitch Muscle Fibers

Slow-twitch fibers Slow-twitch fibers (Type I)(Type I)

Always oxidativeAlways oxidative Resistant to fatigueResistant to fatigue

Red fibersRed fibers Most myoglobinMost myoglobin Good blood supplyGood blood supply Ex. Chicken leg Ex. Chicken leg

marathon runnersmarathon runners

Fast Twitch FibersFast Twitch Fibers Fast-twitch glycolytic fibers (Type Fast-twitch glycolytic fibers (Type

IIb)IIb) White fibers (less myoglobin)White fibers (less myoglobin) Poorer blood supplyPoorer blood supply Susceptible to fatigueSusceptible to fatigue Least enduranceLeast endurance Contract rapidlyContract rapidly Ex. Chicken breast; Ex. Chicken breast;

sprinterssprinters

DisuseDisuseMuscle atrophy when not used; Muscle atrophy when not used;

this is due either to enforced this is due either to enforced bedrest, immobilization, paralysis, bedrest, immobilization, paralysis, etc.etc.

Muscles atrophy 5% of their Muscles atrophy 5% of their strength/day when immobile; thus strength/day when immobile; thus the reason for “skinny” limbs that the reason for “skinny” limbs that have been in a cast.have been in a cast.

MUSCLE and MUSCLE TISSUE

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