physiology 4-muscle-physiology
TRANSCRIPT
PHYSIOLOGY OF MUSCLE PHYSIOLOGY OF MUSCLE CONTRACTIONCONTRACTION
Types of muscle tissueTypes of muscle tissue
StriatedStriated – – skeletal musclesskeletal muscles
StriatedStriated – – cardiac musclecardiac muscle
SmoothSmooth
Physiological properties of musclesPhysiological properties of muscles
ExcitabilityExcitability
ConductivityConductivity
ContractilityContractility
AutomaticityAutomaticity ( (smooth & cardiac smooth & cardiac musclesmuscles))
Physical properties of musclesPhysical properties of muscles
ElasticityElasticity ( (for striatedfor striated))
PlasticityPlasticity ( (for smoothfor smooth))
Skeletal muscles functionsSkeletal muscles functions
1.1. Maintain body postureMaintain body posture 2.2. Body movement in spaceBody movement in space3.3. Body parts movement with regards to Body parts movement with regards to
each othereach other4.4. Enable thermogenesisEnable thermogenesis
SarcomereSarcomere is a structural & is a structural & functional unit of skeletal functional unit of skeletal
musclemuscleIs a part of muscle fiber between 2 Z-linesIs a part of muscle fiber between 2 Z-linesContains transverse tubuliContains transverse tubuli ( (sarcoplasmic sarcoplasmic reticulumreticulum), ), myozin & actin fibers located in myozin & actin fibers located in orderorder
Relaxed sarcomere
Sarcomere in the state of contraction
Contractile elementsContractile elements
ААctinctin –– –– a double helical filament with a double helical filament with tropomyosintropomyosin && troponin troponin attachedattachedММyosinyosin – – asymmetric hexamer with a asymmetric hexamer with a molecular mass 460 kDa. Myosin has a molecular mass 460 kDa. Myosin has a fibrous tail made of 2 intertwined helices.fibrous tail made of 2 intertwined helices.Each helix has a globularEach helix has a globular head portion, head portion, which possesseswhich possesses АТАТPP-а-аsese activityactivity, а , а flexible segmentflexible segment connects head to the tailconnects head to the tail
Motor unit structureMotor unit structure
MOTOR UNITMOTOR UNIT
Consists of motor neuron & a group of Consists of motor neuron & a group of muscle fibers, which are supplied bymuscle fibers, which are supplied by axon axon of this motor neuronof this motor neuronThe number of muscle fibers in one motor The number of muscle fibers in one motor unit depends on the functionunit depends on the function, , which is which is performed by this muscleperformed by this muscle (( from from 10 10 ttо о 30 00030 000 fibers fibers))
ADEQUATE STIMULIADEQUATE STIMULI
Nervous impulseNervous impulse is the only adequate is the only adequate stimulus for skeletal muscle contractionstimulus for skeletal muscle contraction
NEURO-MUSCULAR SYNAPSENEURO-MUSCULAR SYNAPSE
Contact between motor neuron axon & Contact between motor neuron axon & muscle fiber membranemuscle fiber membrane::Axon ending (pre-synaptic membrane)Axon ending (pre-synaptic membrane)Motor endplate (postsynaptic Motor endplate (postsynaptic membrane)membrane)Synaptic cleftSynaptic cleft
AP
AP
AP
EPP
EPP EPP
EPP
Ach
Аch
AP
Са++
Са++
АchАch-receptorAP
Na+
Na+EPP
Cholinesterase
Na+
Na+
Chemical gated channels
Electrical gated channel
STAGESTAGESS OF SYNAPTIC OF SYNAPTIC TRANSMISSIONTRANSMISSION
1. Axon stimulation and excitation of presynaptic membrane.
2. Ca 2+ entry
3. Synaptic vesicles reach presy- naptic membrane and rupture
4. Synaptic transmitter (Ach) is released
5. Combination of Ach and the receptor
6. Excitation of postsynaptic membrane
Mechanism of neuro-muscular Mechanism of neuro-muscular synapse worksynapse work
1.1. Discharge of motor neuron & AP Discharge of motor neuron & AP spreading to axon endingspreading to axon ending
2.2. Opening of calcium voltage gated Opening of calcium voltage gated channelschannels
3.3. Calcium entryCalcium entry4.4. Acetylcholine release at motor endplateAcetylcholine release at motor endplate5.5. Binding of acetylcholine to nicotinic Binding of acetylcholine to nicotinic
acetylcholine receptorsacetylcholine receptors
5.5. Opening of sodium chemically gated Opening of sodium chemically gated channels at endplatechannels at endplate
6.6. Increased sodium conductance in Increased sodium conductance in endplate membraneendplate membrane
7.7. Generation of endplate potential (EPP)Generation of endplate potential (EPP)8.8. Generation of action potential in muscle Generation of action potential in muscle
fibers (due to opening of voltage gated fibers (due to opening of voltage gated sodium channels)sodium channels)
Cross-bridgesCross-bridges
Electro-chemical interactionElectro-chemical interaction
Inward spread of depolarization along T Inward spread of depolarization along T tubulestubulesCharge movement of the slow calcium Charge movement of the slow calcium voltage channel (dihydropyridine receptor) of voltage channel (dihydropyridine receptor) of the transverse tubular membrane the transverse tubular membrane Opening of calcium release channel Opening of calcium release channel (ryanodine receptor) in sarcoplasmic (ryanodine receptor) in sarcoplasmic reticulumreticulumCalcium concentration in sarcoplasm Calcium concentration in sarcoplasm increases 100 timesincreases 100 times
Са++ Са++Са++
SPR
triade
myosin
actinΖ Ζ
dehydropyridin ryanodin
Without AP calcium influx Without AP calcium influx into cytoplasm is impossibleinto cytoplasm is impossible!!!!
Electro-mechanical couplingElectro-mechanical coupling
Calcium binds troponinCalcium binds troponinTropomyosin uncovers myosin binding Tropomyosin uncovers myosin binding sites of actinsites of actinMyosin heads get bound to these active Myosin heads get bound to these active sitessites to form cross-bridgesto form cross-bridges
The sliding filament cross-bridge The sliding filament cross-bridge model model
Thin actin filaments slideThin actin filaments slide along thick along thick myosin ones due to cross-bridges myosin ones due to cross-bridges formationformation
As a result sarcomere & muscle fiber As a result sarcomere & muscle fiber length decreaseslength decreases
Chemo-mechanical interactionChemo-mechanical interaction
Myosin heads bend, allowing actin filaments Myosin heads bend, allowing actin filaments to slide along myosin onesto slide along myosin onesSliding goes smoothly because myosin heads Sliding goes smoothly because myosin heads get attached to the subsequent active centers get attached to the subsequent active centers of actinof actin..The higher is cytoplasm calcium The higher is cytoplasm calcium concentrationconcentration, , the more bridges can be the more bridges can be formed and the stronger is contractionformed and the stronger is contraction
Mechanism of muscle relaxationMechanism of muscle relaxation
Calcium is pumped back into sarcoplasmic Calcium is pumped back into sarcoplasmic reticulumreticulum
Calcium is released from troponinCalcium is released from troponin
Cessation of interaction between actin & Cessation of interaction between actin & myosinmyosin
Energy expenditure during muscle Energy expenditure during muscle contractioncontraction
Na/K pump workNa/K pump workSliding of myosin heads along actin filamentsSliding of myosin heads along actin filamentsCalcium pump workCalcium pump workMost energy is spent for relaxationMost energy is spent for relaxation
Distribution of neuro-muscular Distribution of neuro-muscular synapses in sceletal musclessynapses in sceletal muscles
««All or noneAll or none»» law law
Single muscle fiber obeys this lawSingle muscle fiber obeys this law::Subthreshold irritation doesn’t causeSubthreshold irritation doesn’t cause
contractioncontraction, а, аnd threshold irritation causesnd threshold irritation causes maximal contractionmaximal contraction, , i.ei.e. . the amplitude of the amplitude of muscle contraction doesn’t depend upon muscle contraction doesn’t depend upon the force of irritationthe force of irritation
««All or noneAll or none»» law law
The whole muscle doesn’t obey this law The whole muscle doesn’t obey this law because it consists of many motor units because it consists of many motor units which all have different thresholds of which all have different thresholds of depolarizationdepolarization
Types of contractionTypes of contraction
IsometricIsometric – – tension increase without length tension increase without length increaseincreaseIsotonicIsotonic – – length decrease at the same length decrease at the same tensiontensionMixedMixed - - auxotonicauxotonic
Types of muscle contractionTypes of muscle contraction
TwitchTwitchТеТеtanustanusТоТоnusnus
Types of muscle irritation in Types of muscle irritation in experimentexperiment
Indirect irritationIndirect irritation – – impulse is applied to the impulse is applied to the nervous ending of motor neuronnervous ending of motor neuronDirect irritationDirect irritation– – impulse is applied to the impulse is applied to the muscle directlymuscle directly
Single muscle contraction (twitch)Single muscle contraction (twitch)
CONTRACTIONPHASE
RELAXATION PHASE
LATENT PERIOD
TIME, 0,01 SEC
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+30
АВ
TETANUSTETANUS
Strong & long lasting contraction in Strong & long lasting contraction in response to series of irritationsresponse to series of irritations..Develops due to summation of single Develops due to summation of single muscle contractionsmuscle contractions as the result of as the result of calcium concentration increasecalcium concentration increase
Summation of single contractionsSummation of single contractions
SUMMATION
TIME, 0,01 SEC
SINGLE CONTRACTIONS
““Toothed” tetanusToothed” tetanus
Develops when each subsequent Develops when each subsequent stimulus gets into the period of muscle stimulus gets into the period of muscle relaxationrelaxation so that so that interval between two impulses is less than interval between two impulses is less than the duration of single muscle contractionthe duration of single muscle contraction, , but longer than contraction phasebut longer than contraction phase
TOOTHED TETANUS
Smooth tetanusSmooth tetanus
Each subsequent stimulus is getting Each subsequent stimulus is getting into contraction phase, i.e.into contraction phase, i.e. interval interval between two subsequent stimuli is between two subsequent stimuli is shorter shorter than contraction phase durationthan contraction phase duration, , but but longer than refractory periodlonger than refractory period . .
SMOOTH TETANUS
OPTIMUMOPTIMUM
Is frequency of irritation at which tetanus Is frequency of irritation at which tetanus reaches its maximum amplitudereaches its maximum amplitudeEach subsequent stimulus gets into the Each subsequent stimulus gets into the supernormal period, i.e. right after AP is oversupernormal period, i.e. right after AP is overThis leads to constant high concentration of This leads to constant high concentration of calcium in cytoplasm (calcium pump has no calcium in cytoplasm (calcium pump has no time to switch on)time to switch on)
PESSIMUMPESSIMUM
Is frequency of irritation at which there is no Is frequency of irritation at which there is no summation of contractionssummation of contractionsEach subsequent stimulus gets into the Each subsequent stimulus gets into the refractory period (during the AP refractory period (during the AP development)development)All the sodium channels stay inactivated & All the sodium channels stay inactivated & new AP development is impossiblenew AP development is impossible
OPTIMUM PESSIMUM OPTIMUMSMOOTH
TETANUS
1
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Muscle fibers classificationMuscle fibers classification
Each muscle fiber has just Each muscle fiber has just one synapseone synapse
SlowSlow phasic fibers of oxydative phasic fibers of oxydative typetype
rich in myoglobin & mitohondriarich in myoglobin & mitohondria Red in colourRed in colour Fatigue develops slowlyFatigue develops slowlyVery many fibers in one motor unitVery many fibers in one motor unit ( (up toup to 30 000)30 000)Compose muscles which maintain postureCompose muscles which maintain posture
FastFast phasic fibers of phasic fibers of oxydativeoxydative typetype
Rich in mitohondriaRich in mitohondriaAble to synthesiseAble to synthesise АТ АТPP due to oxydative due to oxydative phosphorylationphosphorylationPerform fast contractionsPerform fast contractionsDevelop fatigue slowlyDevelop fatigue slowlyFewer fibers in one motor unit than in slow Fewer fibers in one motor unit than in slow onesones
FastFast phasicphasic withwith glucolitic glucolitic typetype of of oxydationoxydation
Few mitohondriaFew mitohondriaАТАТPP is formed due to glucolisisis formed due to glucolisisNo myoglobinNo myoglobin ( (white in colourwhite in colour))Quickly contract & develop fatigue quicklyQuickly contract & develop fatigue quicklyLittle number of fibers in one motor unitLittle number of fibers in one motor unit
Tonic fibersTonic fibers
Motor neuron axon forms many synapsesMotor neuron axon forms many synapsesSlowly contract & slowly relaxSlowly contract & slowly relaxLowLow АТ АТPP--asease activity of myosinactivity of myosinForm external muscles of the eyeForm external muscles of the eye
Muscle strengthMuscle strength
Depends on muscle thickness & Depends on muscle thickness & physiological cross sectionphysiological cross section
Muscle workMuscle work
Is energy spent on body movement with a Is energy spent on body movement with a certain force to a certain distansecertain force to a certain distanse::
A = F x SA = F x SIfIf FF=0, =0, thenthen А=0 А=0IfIf SS=0, =0, thenthen А=0 А=0
Maximum work is performed at middle Maximum work is performed at middle loadsloads
Amax=Amax= Fmed x SmaxFmed x Smax
FATIGUEFATIGUE
A process of temporal decrease of muscle A process of temporal decrease of muscle workabilityworkability..Develops due to the decrease of ATP in Develops due to the decrease of ATP in muscle fibermuscle fiber or mediator in neuro-or mediator in neuro-muscular synapsemuscular synapseIn neuro-muscular preparation fatigue In neuro-muscular preparation fatigue develops first of all in the synapsedevelops first of all in the synapse!!
nervemuscle
stimulator stimulator
Muscle at fatigueMuscle at fatigue
Non-fatigued muscle
Orbelli- Genetzynsky phenomenonOrbelli- Genetzynsky phenomenon
Myograme myogramme
FATIGUE IN THE BODYFATIGUE IN THE BODY
Fatigue first develops in the nervous centersFatigue first develops in the nervous centers – – it’s a defense mechanismit’s a defense mechanismMuscles still have reserve of energyMuscles still have reserve of energyproofproof – – Sechenov’s experiments with active Sechenov’s experiments with active restrest
ErgographyErgography
A method of muscle work registrationA method of muscle work registrationErgogramme curve can show signs of Ergogramme curve can show signs of fatiguefatigue::
Decreased magnitude of contractionDecreased magnitude of contractionProlonged phase of relaxationProlonged phase of relaxationDecreased frequency of contractionDecreased frequency of contraction
SMOOTH MUSCLESSMOOTH MUSCLES
Single unit (visceral) smooth Single unit (visceral) smooth musclesmuscles
All internal organsAll internal organsLots of necsusesLots of necsuses ((coloured redcoloured red))Few nervous endingsFew nervous endings ((coloured greencoloured green))
Multiunit smooth musclesMultiunit smooth muscles
Ciliary muscle & Ciliary muscle & musculus dilator pupilimusculus dilator pupiliHave high density of Have high density of neuro-muscular neuro-muscular synapses (coloured synapses (coloured greengreen))
Smooth muscles nervous supplySmooth muscles nervous supply
Muscle cells with nervoussupply
Muscle cells without nervoussupply
Peculiarities of smooth musclesPeculiarities of smooth muscles
Spindle like cells lie close to each otherSpindle like cells lie close to each otherTight contacts between the cellsTight contacts between the cells – – necsusesnecsusesActin & myosin don’t have regular locationActin & myosin don’t have regular locationSarcoplasmic reticulum is developed less Sarcoplasmic reticulum is developed less than in skeletal musclesthan in skeletal muscles
Nervous supply of smooth muscles Nervous supply of smooth muscles Supplied by sympathetic & Supplied by sympathetic & parasympathetic nervesparasympathetic nervesNo synapses, nervous endings form No synapses, nervous endings form varicosesvaricosesMediator is released into the intracellular Mediator is released into the intracellular fluidfluidAfter one cell is excited AP spreads to After one cell is excited AP spreads to other cells along necsusesother cells along necsuses ( (electrical electrical synapsessynapses))The whole muscle contracts The whole muscle contracts simultaneouslysimultaneously ( (functional syncytiumfunctional syncytium))
Adequate stimuliAdequate stimuli
Nervous impulseNervous impulseMechanical stretchingMechanical stretchingChemical substances (hormones)Chemical substances (hormones)
Peculiarities of excitabilityPeculiarities of excitabilityThreshold of depolarization is lower than Threshold of depolarization is lower than in striated musclesin striated musclesMembrane is more permeable for sodium, Membrane is more permeable for sodium, that is why MP is lowerthat is why MP is lower (-50, -60 (-50, -60 mVmV))AP amplitude is lower and its duration is AP amplitude is lower and its duration is longerlongerDepolarization opens up voltage-gated Depolarization opens up voltage-gated calcium channelscalcium channels, , calcium influx slows calcium influx slows down repolarizationdown repolarization
AUTOMATICITYAUTOMATICITY
The ability of cell to generate AP without The ability of cell to generate AP without any external stimuliany external stimuliSmooth muscle cell at the state of rest is Smooth muscle cell at the state of rest is permeable to sodiumpermeable to sodium, , which slowly which slowly depolarizes the cell to the critical level & depolarizes the cell to the critical level & AP developsAP develops
Electrochemical coupling in smooth Electrochemical coupling in smooth musclesmuscles
AP opens up calcium channels,AP opens up calcium channels, calcium calcium enters the cellenters the cell..Ligands activate phospholipaze Ligands activate phospholipaze С С on the on the cell membrane, activation of inositol-3P & cell membrane, activation of inositol-3P & diacylgliceroldiacylglicerol..inositol-3P releases calcium from EPS, inositol-3P releases calcium from EPS, which starts contractionwhich starts contraction
Mechanism of calcium level Mechanism of calcium level regulation in smooth musclesregulation in smooth muscles
in EPS
channel
pumpinositol-3P
receptorligand
Peculiarities of smooth muscles Peculiarities of smooth muscles contractioncontraction
In cytoplasm calcium binds with calmoduline In cytoplasm calcium binds with calmoduline & activates proteinkinase& activates proteinkinase . . ProteinkinaseProteinkinase phosphorilates myosin headphosphorilates myosin head. . Actin-myosin cross-bridges are formedActin-myosin cross-bridges are formedDrop of calcium concentration in myoplasmDrop of calcium concentration in myoplasm causes dephosphorilation of myosin head & causes dephosphorilation of myosin head & cross-bridges are destroyedcross-bridges are destroyed Muscle relaxesMuscle relaxes