Cardiovascular System

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Cardiovascular System - Heart

Contraction of the heart is known as cardiac systole while its relaxation is known as diastole. The heartbeat originates in a specialized cardiac conducting system and is distributed to all parts of the heart musculature (myocardium). Marieb and Katja state that the structures that make up the conducting system are the sinoatrial node (SA node)/ pacemaker, the atrioventricular node (AV node), the internodal atrial pathways, the bundle of His and its branches, and the purkinje system. (Ch. 18)

Ions and Ion channels Involved

The cardiac muscle has three types of ions and membrane ion channels. These ions and their channels play important roles in generating the action potential. They are:

* Sodium ions transported by fast sodium ions

* Slow sodium-calcium channels which conduct sodium and calcium ions

* Potassium channels conducting potassium ions

Events that occur during Cardiac Contractile Action Potential

The events that occur during the cardiac contractile action potential can be described in stages. First, the fast sodium channels open, and there is a rapid upstroke of action potential in the ventricular muscle because of the rapid influx of sodium. According to Guyton, the "plateau" phase takes place, lasting for up to 0.3 seconds (Ch. 10). This is the stage whereby the ventricular action potential is due to the slow opening of the slow sodium-calcium channels. Finally, the membrane potential returns to normal when potassium channels open. This causes large amounts of positive potassium ions to diffuse in an outward direction. Therefore, the membrane potential returns to its resting level.

Similarities and differences

There are differences and similarities between cardiac action potentials, pacemaker potential, and neuronal potential. Cardiac action potential is the action potential that takes place in the cardiac muscles. Pacemaker potential is the action potential experienced at the sinus nodal fiber (sinoatrial node). The sinoatrial node is the place where the heart's action potential originates and is, therefore, known as the heart's pacemaker. Neuronal action potential is action potential experienced in the other parts of the body

Similarities

* Cardiac contractile potential shares most of the similarities with neuronal potential. They both have the same resting membrane potential, that is, -90 millivolts.

* Cardiac contractile