Muscle Muscle Physiology:Physiology:

Muscular System Muscular System FunctionsFunctions

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 Ability of muscle to recoil to original resting length after stretchedlength after 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, Walls of hollow organs, blood vessels, eye,

glands, skinglands, skin Single nucleus centrally locatedSingle nucleus centrally located Not striated, involuntary, gap junctions in Not striated, involuntary, gap junctions in

visceral smoothvisceral smooth CardiacCardiac

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

Skeletal Muscle Skeletal Muscle StructureStructure

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

Organization I:Organization I:

Organization II:Organization II:

Organization III:Organization III:

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

Embryologic origin:Embryologic origin:

Muscle fibre:Muscle fibre:

Internal organization:Internal organization:

Striations:Striations:

Organization of Organization of myofilaments I:myofilaments I:

Organization of Organization of myofilaments II:myofilaments II:

Sliding Filament Model Sliding Filament Model I:I:

Actin myofilaments Actin myofilaments sliding sliding over over myosin to shorten sarcomeresmyosin to shorten 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 During relaxation, sarcomeres

lengthenlengthen

Sliding filament model Sliding filament model II:II:

Sarcomere ShorteningSarcomere Shortening

Structure of Actin and Structure of Actin and MyosinMyosin

Myosin structure:Myosin structure:

Thick filament structure:Thick filament structure:

Structure of the M-line:Structure of the M-line:

Structure of thin Structure of thin filament:filament:

Cross-bridge formation:Cross-bridge formation:

Mechanism of muscle Mechanism of muscle contractioncontraction

Physiology of Skeletal Physiology of Skeletal MuscleMuscle

Nervous systemNervous system Controls muscle Controls muscle

contractions through contractions through action potentialsaction potentials

Resting Resting membranemembrane potentialspotentials Membrane voltage Membrane voltage

difference across difference across membranes membranes (polarized)(polarized)

• Inside cell more Inside cell more negative and more Knegative and more K++

Outside cell more Outside cell more positive and more Napositive and more Na++

Must exist for action Must exist for action potential to occurpotential to occur

Function of Function of Neuromuscular 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 Like camera flash systemsystem

PropagatePropagate Spread from one Spread from one

location to anotherlocation to 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 action potential causes muscle fiber causes muscle fiber contractioncontraction

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

TroponinTroponin

Action Potentials and Action Potentials and Muscle ContractionMuscle Contraction

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 Muscle Length and TensionTension

Stimulus Strength and Stimulus Strength and Muscle ContractionMuscle Contraction

All-or-none law for All-or-none law for muscle fibersmuscle fibers Contraction of equal force Contraction of equal force

in response to each action in 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 Types of Muscle ContractionsContractions

IsometricIsometric: No change in length but : No change in length but tension increasestension increases Postural muscles of bodyPostural muscles of body

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

and muscle shortensand muscle shortens EccentricEccentric: Tension maintained but muscle : Tension maintained but muscle

lengthenslengthens Muscle toneMuscle tone: Constant tension by : Constant tension by

muscles for long periods of timemuscles for long periods of time

Multiple Motor Unit Multiple Motor Unit SummationSummation

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

Multiple-Wave Multiple-Wave SummationSummation

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.

TetanusTetanus Incomplete tetanusIncomplete tetanus

Muscle fibers Muscle fibers partially relax partially relax between contractionbetween contraction

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

TetanusTetanus Complete tetanusComplete tetanus

No relaxation No relaxation between between contractionscontractions

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

TreppeTreppe

Graded responseGraded response Occurs in muscle Occurs in muscle

rested for rested for prolonged periodprolonged period

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

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

Energy SourcesEnergy Sources

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

During resting conditions stores energy to During resting conditions stores energy to synthesize ATPsynthesize ATP

Anaerobic respirationAnaerobic respiration Occurs in absence of oxygen and results in Occurs in absence of oxygen and results in

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

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

More efficient than anaerobicMore efficient than anaerobic

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

Contract more slowly, smaller in diameter, Contract more slowly, smaller in diameter, better blood supply, more mitochondria, more better blood supply, more mitochondria, more fatigue-resistant than fast-twitch fatigue-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 blood supply, fewer and smaller mitochondria than slow-twitchthan slow-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

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 Occurs in neuromuscular junction due to

lack of acetylcholine lack of acetylcholine

Effects of Aging on Effects of Aging on Skeletal MuscleSkeletal Muscle

Reduced Reduced muscle massmuscle mass Increased time for muscle to contract Increased time for muscle to contract

in in responseresponse to nervous stimuli to nervous stimuli Reduced Reduced staminastamina Increased Increased recovery timerecovery time Loss of Loss of muscle fibersmuscle fibers Decreased density of Decreased density of capillariescapillaries in in

musclemuscle

Parts of a MuscleParts of a Muscle