cardiac muscles excitation contraction
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CARDIAC MUSCLESCARDIAC MUSCLES
EXCITATION-CONTRACTION EXCITATION-CONTRACTION COUPLING MECHANISMCOUPLING MECHANISM
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GAP JUNCTIONSGAP JUNCTIONS Proteinaceous tubes that connect Proteinaceous tubes that connect
cellscells Permit ions to flow from one cell to Permit ions to flow from one cell to
another without having to pass from another without having to pass from plasma membrane of the cellplasma membrane of the cell
Dissolved substances such as glucose, Dissolved substances such as glucose, ions can pass through gap junctionsions can pass through gap junctions
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SYNCYTIUMSYNCYTIUM
Action potential can pass from one direction Action potential can pass from one direction to anotherto another
InterconnectionsInterconnections
Two kinds of syncytiumsTwo kinds of syncytiums Atrial syncytiumAtrial syncytium Constitute the walls of 2 atriaConstitute the walls of 2 atria
Ventricular syncytiumVentricular syncytium Constitute the walls of 2 ventriclesConstitute the walls of 2 ventricles
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BARRIERS TO CONDACTIONBARRIERS TO CONDACTION Separation of atria from ventricles by Separation of atria from ventricles by
means of fibrous band tissuemeans of fibrous band tissue High electrical resistanceHigh electrical resistance Propogation of myocardial action Propogation of myocardial action
potential from atria to ventriclespotential from atria to ventricles By specialized conductive system By specialized conductive system
called AV node or AV bundlecalled AV node or AV bundle
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IMPORTANT SEQUENCE OF IMPORTANT SEQUENCE OF TWO SYNCYTIUM STRUCTURESTWO SYNCYTIUM STRUCTURES
The separate structures allow the The separate structures allow the atria to contract in time slightly atria to contract in time slightly before the ventriclesbefore the ventricles
A condition central to cardiac A condition central to cardiac pumping effectivenesspumping effectiveness
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ACTION POTENTIAL IN ACTION POTENTIAL IN CARDIAC MUSCLESCARDIAC MUSCLES
Resting membrane potentialResting membrane potential -85mv to -90mv for normal cardiac -85mv to -90mv for normal cardiac
musclesmuscles -90 to -100mv for specialized fibers -90 to -100mv for specialized fibers
e.g bundle of his, AV nodal fiberse.g bundle of his, AV nodal fibers Magnitude for ventricular muscles Magnitude for ventricular muscles
about 105mv i.e going from about -about 105mv i.e going from about -85mv to +20mv 85mv to +20mv
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IONS AND MYOCARDIAL IONS AND MYOCARDIAL ACTION POTENTIALACTION POTENTIAL
Abrupt change in membrane potentialAbrupt change in membrane potential Corresponds to initial spikeCorresponds to initial spike Depolarization duration=about 0.2 s for Depolarization duration=about 0.2 s for
atrial muscle and 0.3 sec for ventricular atrial muscle and 0.3 sec for ventricular musclesmuscles
Plateau phasePlateau phase Extends the duration of action potential Extends the duration of action potential
significantly 3-15 times more as compared significantly 3-15 times more as compared to skeletal musclesto skeletal muscles
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IONS AND MYOCARDIAL ACTION IONS AND MYOCARDIAL ACTION POTENTIALPOTENTIAL
Sudden opening of fast sodium Sudden opening of fast sodium channelschannels
Allow to enter sodium ions from Allow to enter sodium ions from extracellular fluidextracellular fluid
Fast channelsFast channels Duration of openingDuration of opening Few thousands of secFew thousands of sec Abrupt closureAbrupt closure
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SLOW RESPONSE DUE TO SLOW RESPONSE DUE TO ACTIVATION OF SLOW CALCIUM ACTIVATION OF SLOW CALCIUM
CHANNELSCHANNELS Fast sodium channelsFast sodium channels Slow calcium channelsSlow calcium channels Also called calcium-sodium channelsAlso called calcium-sodium channels Slower to openSlower to open Remain open for several tenths of secRemain open for several tenths of sec Prolonged period of contractionProlonged period of contraction Formation of plateauFormation of plateau
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RECOVERY OF RESTING RECOVERY OF RESTING MEMBRANE POTENTIALMEMBRANE POTENTIAL
Inactivation of sodium-calcium Inactivation of sodium-calcium channelschannels
Membrane permeability of potassium Membrane permeability of potassium increasesincreases
Potassium efflux results in Potassium efflux results in repolarization increasesrepolarization increases
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MYOCARDIAL ACTION MYOCARDIAL ACTION POTENTIALPOTENTIAL
PLATEAU FORMATIONPLATEAU FORMATION
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ACTION POTENTIAL SPREADACTION POTENTIAL SPREAD Over the surfaceOver the surface To interior of fiber along transverse To interior of fiber along transverse
tubulestubules
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EXCITATION-CONTRACTION EXCITATION-CONTRACTION COUPLING MECHANISMCOUPLING MECHANISM
The mechanism by which the action The mechanism by which the action potential causes the myofibrils of potential causes the myofibrils of muscles to contractmuscles to contract
Sarcoplasmic reticulum as a source Sarcoplasmic reticulum as a source of calcium ions in skeletal musclesof calcium ions in skeletal muscles
Diffusion of large quantity of extra Diffusion of large quantity of extra calcium ions from T-tubulescalcium ions from T-tubules
No contraction of cardiac musclesNo contraction of cardiac muscles
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EXCITATION-CONTRACTION EXCITATION-CONTRACTION COUPLING MECHANISMCOUPLING MECHANISM
Less developed sarcoplasmic reticulumLess developed sarcoplasmic reticulum T-tubules have diameter 5 times great T-tubules have diameter 5 times great
as compared to skeletal musclesas compared to skeletal muscles 25 times great volume25 times great volume A large quantity of mucopolysaccharidesA large quantity of mucopolysaccharides Electronegativity chargedElectronegativity charged Binding with abundant source of calcium Binding with abundant source of calcium
ionsions
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EXCITATION-CONTRACTION EXCITATION-CONTRACTION COUPLING MECHANISMCOUPLING MECHANISM
Concentration of calcium ions in Concentration of calcium ions in extracellular fluidextracellular fluid
Opening of T-tubules pass directly Opening of T-tubules pass directly through cell membrane into through cell membrane into extracellular spacesextracellular spaces
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EXCITATION-CONTRACTION EXCITATION-CONTRACTION COUPLING MECHANISMCOUPLING MECHANISM
Permission of percolation of calcium Permission of percolation of calcium ions from extracellular fluidions from extracellular fluid
Dependence of contraction on Dependence of contraction on calcium ions from extracellular fluidcalcium ions from extracellular fluid
Comparison to skeletal musclesComparison to skeletal muscles Cessation of contraction Cessation of contraction Pump systemPump system T-tubules extracellular fluidT-tubules extracellular fluid
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OVERALL VIEW OF CONTRACTION OVERALL VIEW OF CONTRACTION OF SKELETAL AND CARDIAC OF SKELETAL AND CARDIAC
MUSCLESMUSCLES SKELETAL MUSCLESSKELETAL MUSCLES Highly developed Highly developed
sarcoplasmic sarcoplasmic reticulumreticulum
Less developed T-Less developed T-systemsystem
No electronegativityNo electronegativity Extracellular fluid is Extracellular fluid is
not effieciennot effiecien
CARDIAC MUSCLESCARDIAC MUSCLES Less developed Less developed
sarcoplasmic sarcoplasmic reticulumreticulum
Highly developed T-Highly developed T-systemsystem
ElectronegativityElectronegativity Extracellular fluid is Extracellular fluid is
effiecient and major effiecient and major source of calcium ionssource of calcium ions