Question

Describe how the heartbeat is controlled and maintained

Answer 1

• 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.