What is Sinoatrial (SA) node ?

Key Features of the SA Node

1. Automaticity:

• The SA node cells can generate electrical impulses automatically without external stimulation.
• This is due to their ability to depolarize spontaneously at a regular rate.

2. Heart Rate Regulation:

• The SA node sets the basic rhythm of the heart, typically between 60-100 beats per minute in a resting adult.
• Its activity can be influenced by the autonomic nervous system:
• Sympathetic stimulation: Increases heart rate (e.g., during stress or exercise).
• Parasympathetic stimulation (via the vagus nerve): Decreases heart rate (e.g., during rest).

3. Impulse Transmission:

• The electrical signal generated by the SA node spreads through the walls of the atria, causing them to contract and push blood into the ventricles.
• The signal then reaches the atrioventricular (AV) node, where it is delayed slightly to allow the ventricles to fill before contracting.

Importance of the SA Node:

• It ensures that the heart beats in a coordinated and rhythmic manner, effectively pumping blood to the lungs and the rest of the body.
• If the SA node malfunctions, other parts of the heart, such as the AV node, can take over as pacemakers, but at a slower rate. This can lead to arrhythmias or irregular heartbeats.

Clinical Relevance

• Bradycardia: When the SA node fires too slowly, leading to a slower heart rate.
• Tachycardia: When the SA node fires too quickly, resulting in an abnormally fast heart rate.
• Pacemaker Implantation: In cases where the SA node is not functioning properly, an artificial pacemaker may be implanted to regulate the heart rate.

Understanding the SA node is essential in grasping the heart’s electrical conduction system and its role in maintaining life.