Show Clin Anat. 2009 Jan;22(1):99-113.
An organized rhythmic contraction of the heart requires adequate propagation of electrical impulses along the conduction pathway. Of note, the impulses in the His-Purkinje system travel in such a way that papillary muscle contraction precedes that of the ventricles, thereby preventing regurgitation of blood flow through the AV valves. ElectrophysiologyPhysiol Rev. 2005 Oct;85(4):1205-53. Ion channelsHeart Rhythm. 2010 Jan;7(1):117-26.
Properties of cardiac ion channels
Note: The different types of cardiac ion channels are discussed below, throughout the description of the phases of action potentials in different cardiac cells. Action potentials and impulse conductionPhysiol Rev. 2005 Oct;85(4):1205-53. Action potential: electrical stimulation created by a sequence of ion fluxes through specialized channels in the membrane (sarcolemma) of cardiomyocytes that leads to cardiac contraction. Action potential in cardiomyocytesThe action potential in typical cardiomyocytes is composed of 5 phases (0-4), beginning and ending with phase 4. Phase 4: The resting phase
Phase 0: Depolarization
Phase 1: Early repolarization
Phase 2: The plateau phase
Phase 3: Repolarization
Action potential in cardiac pacemaker cellsPharmacol Ther. 2005 Jul;107(1):59-79.
Table 1. Cardiac cell types displaying pacemaker behavior.
The sequence of events for pacemaker action potential:
Implications of pacemaker activity on global cardiac depolarization
Refractory period
Sequence of depolarization
Excitation-contraction couplingNature. 2002 Jan 10;415(6868):198-205. Excitation-contraction coupling represents the process by which an electrical action potential leads to contraction of cardiac muscle cells. This is achieved by converting a chemical signal into mechanical energy via the action of contractile proteins. Calcium is the crucial mediator that couples electrical excitation to physical contraction by cycling in and out of the myocyte’s cytosol during each action potential. Contractile proteinsMain contractile elements:
Regulatory elements:
Calcium-induced calcium release (CICR)The initial influx of Ca2+ into myocytes through L-type Ca2+ channels during phase 2 of the action potential is insufficient to trigger contraction of myofibrils. This signal is amplified by the CICR mechanism, which triggers much greater release of Ca2+ from the sarcoplasmic reticulum.
Contractile cycle
Myocyte relaxationAs with myocyte contraction, this process is synchronized with the electrical activity of the cell.
Neural modulation of contractilityAdv Physiol Educ. 2011 Mar;35(1):28-32.
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