Explain the electrical activity of the heart during a heart beat

Figure 9

The heart is myogenic (self stimulated), it works by two parts of the nervous system. The sympathetic part of the nervous system accelerates the heart beat, this helps to meet the bodies demands ie when exercising, and the parasympathetic system stops and slows things down.
The rhythmic sequence of contractions (heart beat) is coordinated by the sino atrial (SA), and atrio ventricular (AV) nodes. The upper wall of the right atrium is where the SA node is located and is responsible for sending electrical impulses that initiates atrial contraction. Once the impulse reaches the lower right atrium where the AV node is situated, the impulse remains static for a short period of time, allowing all the blood in the atria to fill the ventricles, before being conducted through several structures which leads to contraction of the ventricles. (Class notes, 2010)