Origin of Heart Beat and Its Conduction
Action Potential
Fast Response AP
Slow response AP
in most myocardial tissue (atria, ventricle and Purkinje fiber of conducting system
in specialized cell responsible for pacemaker activity of heart (SA and NA node)
Ionic basis
Cardiac Conducting System
Differences
1) Resting membrane potential
2) rate of depolarisation
3) Propagation of AP through heart
Ventricular potential
Pacemaker potential
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AV node
Bundle of His
Internodal node
Right and left bundle branches
Interatrial tract (Bachmann's bundle)
Purkinje fibers
SA node
Properties of cardiac muscle
Rhythmicity
Conductivity
Mechanism of sinus nodal rhythmicity
RMP of sinus node: -55 to -66 mV
Na+ channel mainly inactivated, Na+-Ca2+ channel open, atrial node AP start develop, then the AP will return to negative state
it's myogenic in origin
initiated by SA node
the ability of cardiac muscle to contract in a regular constant manner without nerve supply
the ability of cardiac muscle fiber to conduct the cardiac impulses that are initiated in SA node.
fastest conduction of velocity- Purkinje fibre
The slowest conduction of velocity- AV node
importance- allow sufficient time for ventricle to be filled with blood before they contract
because it has few number of intercalated disc
importance: allow the 2 ventricle to contract at the same time simultaneously
Cardiac innervation
Sympathetic stimuli
Parasympathetic Stimuli
Tachycardia, increase depolarization of SA node
1) decrease SA node permeability to K+ >>> less K+ efflux
2) increase membrane potential to Ca2+ >>> more Ca2+ influx
3) As result, the slope of depolarisation increase, cause increase of SA node firing and increase HR
Bradycardia, decrease depolarization of SA node
2) decrease membrane permeability to Ca2+ >>> less Ca2+ influx
3) As result, the prepotential slope decrease, cause decrease rate of SA node firing and decrease HR
1) increase SA node permeability to K+>>>> more K+ efflux