What are the 5 phases of cardiac action potential?
What are the 5 phases of cardiac action potential?
Resting (4), upstroke (0), early repolarization (1), plateau (2), and final repolarization are the 5 phases of the action potential. A decline of potential at the end of phase 3 in pacemaker cells, such as the sinus node, is shown as a broken line.
What is depolarization of cardiac muscle?
Once the threshold potential is reached, L-type calcium channels open, calcium ions enter the cell, and depolarization occurs. In contrast to the cardiac myocyte action potential, there is no inward movement of sodium ions during depolarization.
What phase is depolarization?
Phase 0
Phase 0 is the phase of depolarization; Phase 1 through 3 is the phases during which repolarization occurs; Phase 4 is the resting phase with no spontaneous depolarization. During phase zero, the phase of rapid depolarization, voltage-gated Na+ channels open, resulting in a rapid influx of Na+ ions.
What is depolarization and repolarization of heart?
Depolarization with corresponding contraction of myocardial muscle moves as a wave through the heart. 7. Repolarization is the return of the ions to their previous resting state, which corresponds with relaxation of the myocardial muscle. 8.
How do cardiac cells depolarize?
Synchronous contraction: all cardiomyocytes (including pacemaker cells) are electrically coupled through gap junctions. An action potential in one cell will cause all neighbouring cells to depolarize, allowing the heart chambers to act as a unit.
Which of the following occurs during depolarization of a cardiac cell?
Which of the following occurs during depolarization of a cardiac cell? The cell becomes relatively more positively charged.
What happens depolarization?
The depolarization, also called the rising phase, is caused when positively charged sodium ions (Na+) suddenly rush through open voltage-gated sodium channels into a neuron. As additional sodium rushes in, the membrane potential actually reverses its polarity.
What happens during phase 4 of the cardiac action potential?
In these cells, phase 4 is also known as the pacemaker potential. During this phase, the membrane potential slowly becomes more positive, until it reaches a set value (around -40 mV; known as the threshold potential) or until it is depolarized by another action potential, coming from a neighboring cell.
Where does depolarization of the heart begin?
right atrium
The wave of depolarization begins in the right atrium, and the impulse spreads across the superior portions of both atria and then down through the contractile cells. The contractile cells then begin contraction from the superior to the inferior portions of the atria, efficiently pumping blood into the ventricles.
What is associated with the depolarization phase of the cardiac cycle?
Atrial depolarization initiates contraction of the atrial musculature. As the atria contract, the pressure within the atrial chambers increases, which forces more blood flow across the open atrioventricular (AV) valves, leading to a rapid flow of blood into the ventricles.
What are the 4 phases of cardiac cycle?
The cardiac cycle involves four major stages of activity: 1) “Isovolumic relaxation”, 2) Inflow, 3) “Isovolumic contraction”, 4) “Ejection”.
Which of the following phases of the cardiac action potential occurs as a response to ventricular depolarization?
Phase 0. This phase consists of a rapid, positive change in voltage across the cell membrane (depolarization) lasting less than 2 ms, in ventricular cells and 10/20 ms in SAN cells. This occurs due to a net flow of positive charge into the cell.