The Heartbeat
- The heart is capable of contracting and relaxing rhythmically without fatigue due to its special muscles called cardiac muscles.
- The rhythmic contraction of the heart arise from within the heart muscles without nervous stimulation.
- The contraction is said to be myogenic.
- The heartbeat is initiated by the pacemaker or sino-artrio-node (SAN) which is located in the right atrium.
- The wave of excitation spreads over the walls of atria.
- It is picked by the artrio-ventricular node which is located at the junction:
- Of the atria and ventricles, from where the purkinje tissue spreads the wave to the walls of the ventricles.
- The heart contracts and relaxes rhythmically at an average rate of 72 times per minute.
- The rate of the heartbeat is increased by the sympathetic nerve, while it is slowed down by the vagus nerve.
Heartbeat is also affected by hormones e.g. adrenaline raises the heartbeat