Action Potentials and The Cardiac Cycle Essay Example | Topics and Well Written Essays - 1750 words

Action Potentials and The Cardiac Cycle - Essay Example ld take approximately 200 to 500 milliseconds to complete and conducted from cell to cell, slower compared to less than 2 milliseconds in the action potentials in skeletal muscles (Seeley, Stephens, and Tate, 2007: 333). The following figures depict the stages or phases of an action potential: resting potential, depolarization, repolarization, and returning to resting potential or the final repolarization phase. The resting potential is the stage when the cell is not conducting an impulse (Rothenberg and Chapman, 1989). At this resting stage, the concentration of sodium (Na+) ions is higher outside the cell than the inside. On the other hand, the potassium (K+) ions are evidently higher inside the cell, compared to the outside. In this manner, the sodium-potassium pump is constantly at work to ensure a more positive ionic environment outside the cell membrane, thus leaving the cell interior highly negative (MCB-HHMI Outreach, 2005). Depolarization marks the first step in sending a signal or action potential, wherein the negatively charged cell interior is disturbed by the entrance positive Na+ ions, as we can see in the above figure (MCB-HHMI Outreach, 2005). Further, it is in this stage that Na+ channels open to give way to the diffusion of Na+ into the cell, at the same time, the K+ channels would just begin to open but closes immediately to decrease the permeability of cell to K+ (Seeley, Stephens, and Tate, 2007: 333). We can notice in figure 2 that the potassium and sodium channels are like gates that open to give way to their respective ions. Accordingly, the opening and closing of these membrane channels are responsible in the production of action potentials, as a result of the changes in cellular membrane permeability (Seeley, Stephens, and Tate, 2007: 333). In addition, calcium (Ca++) channels slowly open to cause Ca++ ions to diffuse into the cell, which also mimic depolarization (Seeley, Stephens, an d Tate, 2007: 333). An action potential triggers