The intricate nodal musculature

Hyderabad: This article is in continuation to the previous article that discussed about the human blood circulatory system and the functions of a human heart. In this article we will discuss about the nodal tissue.

Nodal Tissue: – A specialised cardiac musculature called the nodal tissue is also distributed in the heart.

– A patch of this tissue is present in the right upper corner of the right atrium called the sino-atrial node (SAN).

– Another mass of this tissue is seen in the lower left corner of the right atrium close to the atrio-ventricular septum called the atrio-ventricular node (AVN).
– A bundle of nodal fibres, atrio-ventricular bundle (AV bundle) continues from the AVN which passes through the atrio-ventricular septa to emerge on the top of the inter-ventricular septum and immediately divides into a right and left bundle.

– These branches give rise to minute fibres throughout the ventricular musculature of the respective sides and are called Purkinje fibres.
– The nodal musculature has the ability to generate action potentials without any external stimuli, i.e., it is auto-excitable.

However, the number of action potentials that could be generated in a minute vary at different parts of the nodal system.
-The SAN can generate the maximum number of action potentials, i.e., 70-75 min–1, and is responsible for initiating and maintaining the rhythmic contractile activity of the heart. Therefore, it is called the pacemaker.
– Our heart normally beats 70-75 times in a minute (average 72 beats min–1).