Myogenic stimulation of the heart and transmission of a subsequent wave of electrical activity. Roles of the sinoatrial node (SAN), atrioventricular node (AVN) and bundle of His.

Myogenic stimulation means that the heart is caused to move because of signals that originate inside of it. In normal muscles movement is caused by signals from the CNS.

The signals come from the sinoartrial node (SNA) which is sometimes refered to as the pace maker. Although the signals for the cardiac cycle are generated in the heart, the pace is controlled by signals from the brain.

• SNA sends electrical activity accross the top of the atria (they contract)
• The atrioventricular septum is non-conductive tissue which stops the signal going down the sides.
• The signal that travelled down between the atria reaches the atrioventricular node (AVN).
• The AVN delays the signal (so that the atria fully contract) before transmitting it again.
• The electrical activity now travels down the bundle of His.
• The signal reaches the bottom of the ventricles where it causes them to contract.

Its important that the ventricles contract upwards so that the blood is being pushed towards the semi-lunar valves.

It is also of importance that the AVN delays the signal long enough for the atria to finish their contraction- so that the most blood possible goes into the ventricle before it starts contracting and closes the atrio-ventricluar valves.