Cardiac action potential action potential (see phase 2, below) and is a fundamental step in cardiac excitation-contraction coupling. There are important physiological differences between the cells that spontaneously generate the action potential (pacemaker cells; e.g. SAN) and those that simply conduct it (non-pacemaker cells; e.g. ventricular myocytes). The specific differences in the types of ion channels expressed and mechanisms by which they are activated results in differences in the configuration of the action potential waveform, as shown in figure 2. The standard model used to understand the cardiac action potential is that of the ventricular myocyte. Outlined below are the five phases of
Cardiac physiology large numbers of gap junctions that allow the passage of ions between the cells and help to synchronize the contraction. Intercellular connective tissue also helps to strongly bind the cells together, in order to withstand the forces of contraction. Cardiac muscle undergoes aerobic respiration patterns, primarily metabolizing lipids and carbohydrates. Oxygen from the lungs attaches to haemoglobin and is also stored in the myoglobin, so that a plentiful supply of oxygen is available. Lipids, and glycogen are also stored within the sarcoplasm and these are broken down by mitochondria to release ATP. The cells undergo twitch-type contractions with long refractory