Question

A group of specialised cardiac muscles in the wall of right atrium that initaites heartbeat.

Answer 1

A group of specialised muscle cells present at the base of the vena cava in the right atrium autonomously depolarises to generally initiate contraction.

It is called the SA node or Sinoatrial node.

The SA node cells do not have a stable resting potential. Rather, they repeatedly depolarize to threshold spontaneously. The spontaneous depolar- ization is a pacemaker potential. When the pacemaker potential reaches threshold, it triggers an action potential. Following the action potential, the two atria contract at the same time.