Assertion : Sino-atrial node (SAN) is called the pacemaker
Reason : SAN generates the maximum number of action potentials and is responsible for intiating and maintaining the rhythmic contractions of the heart.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion
B. If both assertion and reason are true but reason is not the correct explanation of assertion
C. If assertion is true but reason is false
D. If both assertion and reason are false

Answer

A

Explanation

In the myogenic heart, contraction is initiated by specilised muscle. The SAN can generated the maximum number of action potentials, i.e., `70-75 min^(-1)` and is responsible for intiating and maintaining the rhythmic contractile activity of the heart. Therefore, it is called the pacemaker. The SAN controls the beat of the heart because its rate of rhythmical discharge is faster than that of any other part of the heart. Therefore, the SAN is virtually always the pacemaker of the normal heart.