Working Cell Process

Heart is a muscular organ located in the thoracic cavity; it is responsible for pumping the blood to rest of the body through the circulatory system.1 It is composed of four chambers: left & right atrium and ventricle, these two chambers are separated by valves(atrioventricular), whereas the left and right side of heart is separated by interventricular septum.1 Walls of heart are composed of cardiac myocytes, these cells contain myofilaments, each unit is composed of contractile protein called actin and myosin.3 There are also regulatory proteins such as troponin which binds to actin filament, preventing the myosin head from binding to actin, is found within the myocytes.3 Each myofilament is surrounded by sarcoplasmic reticulum which stores calcium and adjacent cardiac myocyte are joined in an end to end …show more content…
There are five phases of action potential in working cells: during phase 0, fast sodium channel opens allowing sodium ion (Na+)to enter the cell and depolarize it; during phase 1, membrane permeability to Na+ decreases, partially repolarizing the cell; during phase 2, L-type Ca2+ channel opens allowing extracellular Ca2+ to influx to maintain and prolong action potential; potassium ion rushes into the cell during phase 3, and together with the inactivation of Ca2+ channel, repolarization occurs; cell then return to resting potential in phase 4.2 Calcium ion influx into the cell not only prolongs action potential but also causes muscle contraction by binding to troponin removing it from the actin filament to allow myosin head to bind to actin and cause cross-bridge reaction which then cause contraction.2 In addition, these orderly depolarization triggers waves of