skeletal muscle excitation and...

Skeletal Muscle Skeletal Muscle Excitation and Excitation and ContractionContraction

Nurhadi Ibrahim Nurhadi Ibrahim Nani Cahyani SudarsonoNani Cahyani Sudarsono

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The ObjectivesThe Objectives

.١.١ Muscular System FunctionsMuscular System Functions

.٢.٢ Skeletal Muscle StructureSkeletal Muscle Structure

.٣.٣ Skeletal Muscle ContractionSkeletal Muscle Contraction

Muscular System FunctionsMuscular System Functions

• Body movementBody movement• Maintenance of postureMaintenance of posture• RespirationRespiration• Production of body heatProduction of body heat• CommunicationCommunication• Constriction of organs and vesselsConstriction of organs and vessels• Heart beatHeart beat

Properties of MuscleProperties of Muscle

• ContractilityContractility– Ability of a muscle to shorten with forceAbility of a muscle to shorten with force

• ExcitabilityExcitability– Capacity of muscle to respond to a stimulusCapacity of muscle to respond to a stimulus

• ExtensibilityExtensibility– Muscle can be stretched to its normal resting Muscle can be stretched to its normal resting

length and beyond to a limited degreelength and beyond to a limited degree• ElasticityElasticity

– Ability of muscle to recoil to original resting length Ability of muscle to recoil to original resting length after stretchedafter stretched

Muscle Tissue TypesMuscle Tissue Types• SkeletalSkeletal

– Attached to bonesAttached to bones– Nuclei multiple and peripherally locatedNuclei multiple and peripherally located– Striated, Voluntary and involuntary (reflexes)Striated, Voluntary and involuntary (reflexes)

• SmoothSmooth– Walls of hollow organs, blood vessels, eye, glands, Walls of hollow organs, blood vessels, eye, glands,

skinskin– Single nucleus centrally locatedSingle nucleus centrally located– Not striated, involuntary, gap junctions in visceral Not striated, involuntary, gap junctions in visceral

smoothsmooth• CardiacCardiac

– HeartHeart– Single nucleus centrally locatedSingle nucleus centrally located– Striations, involuntary, intercalated disksStriations, involuntary, intercalated disks

Skeletal Muscle StructureSkeletal Muscle Structure

• Muscle Muscle fibersfibers or or cellscells– Develop from Develop from

myoblastsmyoblasts– Numbers remain Numbers remain

constantconstant• Connective tissueConnective tissue• Nerve and blood Nerve and blood

vesselsvessels

OrganizationOrganization

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

M us c le s truc tureM us c le s truc ture

Sarcomere


Connective Tissue, Nerve, Connective Tissue, Nerve, Blood VesselsBlood Vessels

• Connective tissueConnective tissue– External laminaExternal lamina– EndomysiumEndomysium– PerimysiumPerimysium– FasciculusFasciculus– EpimysiumEpimysium

• FasciaFascia• Nerve and blood Nerve and blood

vesselsvessels– AbundantAbundant

Organization of myofilaments Organization of myofilaments

Sliding Filament Model I:Sliding Filament Model I:

• Actin myofilaments Actin myofilaments sliding sliding over myosin to over myosin to shorten sarcomeresshorten sarcomeres– Actin and myosin do not change lengthActin and myosin do not change length– Shortening sarcomeres responsible for Shortening sarcomeres responsible for

skeletal muscle contractionskeletal muscle contraction• During relaxation, sarcomeres lengthenDuring relaxation, sarcomeres lengthen

Sliding filament model II:Sliding filament model II:

Sarcomere ShorteningSarcomere Shortening

Structure of Actin and MyosinStructure of Actin and Myosin

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Skeletal Muscle ContractionSkeletal Muscle Contraction

Cross-bridge formation:Cross-bridge formation:

Mechanism of muscle Mechanism of muscle contractioncontraction

Function of Neuromuscular Function of Neuromuscular JunctionJunction

Action PotentialsAction Potentials• PhasesPhases

– DepolarizationDepolarization• Inside plasma Inside plasma

membrane becomes membrane becomes less negativeless negative

– RepolarizationRepolarization• Return of resting Return of resting

membrane potentialmembrane potential• All-or-none principleAll-or-none principle

– Like camera flash systemLike camera flash system• PropagatePropagate

– Spread from one location Spread from one location to anotherto another

• FrequencyFrequency– Number of action Number of action

potential produced per potential produced per unit of timeunit of time

Excitation-Contraction Excitation-Contraction CouplingCoupling

• Mechanism where an Mechanism where an action potential causes action potential causes muscle fiber muscle fiber contractioncontraction

• InvolvesInvolves– SarcolemmaSarcolemma– Transverse or T tubulesTransverse or T tubules– Terminal cisternaeTerminal cisternae– Sarcoplasmic reticulumSarcoplasmic reticulum– CaCa2+2+

– TroponinTroponin

Action Potentials and Muscle Action Potentials and Muscle ContractionContraction

Muscle TwitchMuscle Twitch

• Muscle contraction Muscle contraction in response to a in response to a stimulus that stimulus that causes action causes action potential in potential in one or one or moremore muscle fibers muscle fibers

• PhasesPhases– Lag or latentLag or latent– ContractionContraction– RelaxationRelaxation

Muscle Length and TensionMuscle Length and Tension

Stimulus Strength and Muscle Stimulus Strength and Muscle ContractionContraction

• All-or-none law for muscle All-or-none law for muscle fibersfibers– Contraction of equal force in Contraction of equal force in

response to each action response to each action potentialpotential

• Sub-threshold stimulusSub-threshold stimulus• Threshold stimulusThreshold stimulus• Stronger than thresholdStronger than threshold

• Motor unitsMotor units– Single motor neuron and all Single motor neuron and all

muscle fibers innervatedmuscle fibers innervated• Graded for whole musclesGraded for whole muscles

– Strength of contractions Strength of contractions range from weak to strong range from weak to strong depending on stimulus depending on stimulus strengthstrength

Types of Muscle ContractionsTypes of Muscle Contractions

• IsometricIsometric: No change in length but tension : No change in length but tension increasesincreases– Postural muscles of bodyPostural muscles of body

• IsotonicIsotonic: Change in length but tension : Change in length but tension constantconstant– ConcentricConcentric: Overcomes opposing resistance and : Overcomes opposing resistance and

muscle shortensmuscle shortens– EccentricEccentric: Tension maintained but muscle : Tension maintained but muscle

lengthenslengthens• Muscle toneMuscle tone: Constant tension by muscles for : Constant tension by muscles for

long periods of timelong periods of time

Multiple Motor Unit Multiple Motor Unit SummationSummation

• A whole muscle contracts with a small or large A whole muscle contracts with a small or large force depending on number of motor units force depending on number of motor units stimulated to contractstimulated to contract

Multiple-Wave SummationMultiple-Wave Summation

• As frequency of action As frequency of action potentials increase, potentials increase, frequency of contraction frequency of contraction increasesincreases

• Action potentials come Action potentials come close enough together so close enough together so that the muscle does not that the muscle does not have time to completely have time to completely relax between relax between contractions.contractions.

– Incomplete tetanusIncomplete tetanus

• Muscle fibers partially Muscle fibers partially relax between relax between contractioncontraction

• There is time for Ca There is time for Ca 2+2+ to be recycled through to be recycled through the SR between action the SR between action potentialspotentials

– Complete tetanusComplete tetanus

• No relaxation between No relaxation between contractionscontractions

• Action potentials come Action potentials come sp close together that sp close together that Ca Ca 2+2+ does not get re- does not get re-sequestered in the SRsequestered in the SR

TreppeTreppe• Graded responseGraded response• Occurs in muscle Occurs in muscle

rested for prolonged rested for prolonged periodperiod

• Each subsequent Each subsequent contraction is stronger contraction is stronger than previous until all than previous until all equal after few stimuli equal after few stimuli

Speed of contraction:Speed of contraction:

Sustained sub-maximal tension:Sustained sub-maximal tension:

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Metabolism for muscle contraction

Energy SourcesEnergy Sources

• ATP provides immediate energy for muscle ATP provides immediate energy for muscle contractions from contractions from 3 sources3 sources– Creatine phosphateCreatine phosphate

• During resting conditions stores energy to synthesize During resting conditions stores energy to synthesize ATPATP

– Anaerobic respirationAnaerobic respiration• Occurs in absence of oxygen and results in breakdown Occurs in absence of oxygen and results in breakdown

of glucose to yield of glucose to yield ATPATP and lactic acid and lactic acid– Aerobic respirationAerobic respiration

• Requires oxygen and breaks down glucose to produce Requires oxygen and breaks down glucose to produce ATPATP, carbon dioxide and water, carbon dioxide and water

• More efficient than anaerobicMore efficient than anaerobic

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Energy for Contraction

Vander, Sherman, Luciano's Human Physiology: The Mechanisms of Body Function, 9/e

Slow and Fast FibersSlow and Fast Fibers• Slow-twitch or Slow-twitch or high-oxidativehigh-oxidative

– Contract more slowly, smaller in diameter, better Contract more slowly, smaller in diameter, better blood supply, more mitochondria, more fatigue-blood supply, more mitochondria, more fatigue-resistant than fast-twitch resistant than fast-twitch

• Fast-twitch or Fast-twitch or low-oxidativelow-oxidative– Respond rapidly to nervous stimulation, contain Respond rapidly to nervous stimulation, contain

myosin to break down ATP more rapidly, less myosin to break down ATP more rapidly, less blood supply, fewer and smaller mitochondria than blood supply, fewer and smaller mitochondria than slow-twitchslow-twitch

• Distribution of Distribution of fast-twitch and slow twitchfast-twitch and slow twitch– Most muscles have both but varies for each Most muscles have both but varies for each

musclemuscle• Effects of exerciseEffects of exercise

– HypertrophiesHypertrophies: Increases in muscle size: Increases in muscle size– AtrophiesAtrophies: Decreases in muscle size: Decreases in muscle size

Slow and Fast Fibers:Slow and Fast Fibers:

FatigueFatigue• Decreased capacity to work and Decreased capacity to work and

reduced efficiency of performancereduced efficiency of performance• Types:Types:

– PsychologicalPsychological• Depends on Depends on emotional stateemotional state of individual of individual

– MuscularMuscular• Results from Results from ATPATP depletion depletion

– SynapticSynaptic• Occurs in neuromuscular junction due to lack of Occurs in neuromuscular junction due to lack of

acetylcholine acetylcholine

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ConclusionsConclusions1.1. Skeletal muscle contraction is played by Skeletal muscle contraction is played by

actin and myosinactin and myosin2.2. Skeletal muscle contractionSkeletal muscle contraction and

relaxation need ATPATP3.3. Ion Calcium is play important in Ion Calcium is play important in

Skeletal muscle contractionSkeletal muscle contraction and relaxation

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Nurhadi IbarahimNani Cahyani Sudarsono

skeletal muscle excitation and...

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