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Describe how the heartbeat is controlled and maintained

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  • 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.
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