Q.Sino-atrial node is called the pacemaker of our heart. Why?

The sino-atrial node is called the pacemaker because it sets the pace at which the whole heart beats.

• The SAN is a patch of nodal tissue lying in the right upper corner of the right atrium.
• Like all nodal tissue it is autoexcitable, generating its own action potentials.
• Among all parts of the nodal system, the SAN generates the greatest number of action potentials — about seventy to seventy-five per minute. …

The heart's nodal tissue is autoexcitable, meaning several of its parts are capable of generating action potentials on their own. But these different parts do not fire at the same rate — the rate at which action potentials are produced differs from one region of the nodal system to another. This difference in rate is exactly what makes one region the leader.

The sino-atrial node, or SAN, is a small patch of nodal tissue sitting in the right upper corner of the right atrium. It generates the greatest number of action potentials of any part of the nodal system — about seventy to seventy-five per minute. Because it is the fastest to fire, its signals reach the rest of the heart before any slower region can act on its own, and so the SAN sets and sustains the rhythmic contractions of the heart. …

Method: Explaining Why One Structure "Leads" Among Several Similar Structures

Use this approach whenever a question asks why one part of a system dominates others that share the same basic property.

Steps

Step 1: Establish that all the candidate structures share the base property

Every part of the nodal tissue is autoexcitable — capable of generating its own impulses — so the leadership can't be explained by that shared property alone.

Step 2: Identify the ONE measurable quantity that differs between them

Here it is the rate at which each region generates action potentials.

Step 3: State the actual comparative values …