Describe tha conducting system of human …

A cardiac conduction system is a group of specialized cardiac muscle cells in the walls of the heart that send signals to the heart muscle causing it to contract. The main components of the cardiac conduction system are the SA node, AV node, the bundle of His, bundle branches, and Purkinje fibers.

The sequence of electrical events during one full contraction of the heart muscle:

• An excitation signal (an action potential) is created by the sinoatrial (SA) node.
• The wave of excitation spreads across the atria, causing them to contract.
• Upon reaching the atrioventricular (AV) node, the signal is delayed.
• It is then conducted into the bundle of His, down the interventricular septum.
• The bundle of His and the Purkinje fibers spread the wave impulses along the ventricles, causing them to contract.

Components of the Cardiac Conduction System:

1. Sinoatrial Node: The sinoatrial (SA) node is a collection of specialized cells (pacemaker cells), and is located in the upper wall of the right atrium, at the junction where the superior vena cava enters. These pacemaker cells can spontaneously generate electrical impulses. The wave of excitation created by the SA node spreads via gap junctions across both atria, resulting in atrial contraction (atrial systole) – with blood moving from the atria into the ventricles.
2. Atrioventricular Node (AV Node) - The AV Node receives the signal from the SA Node with the help of Bachmann's Bundle. It takes a 0.1s delay for the signal to transmit from the AV node to the Bundle of His.
3. Atrioventricular Bundle:  The atrioventricular bundle (bundle of His) is a continuation of the specialized tissue of the AV node, and serves to transmit the electrical impulse from the AV node to the Purkinje fibers of the ventricles. It descends down the membranous part of the interventricular septum, before dividing into two main bundles: Right bundle branch – conducts the impulse to the Purkinje fibres of the right ventricle. Left bundle branch – conducts the impulse to the Purkinje fibers of the left ventricle.
4. The Purkinje fibers (sub-endocardial plexus of conduction cells) are a network of specialized cells. They are abundant with glycogen and have extensive gap junctions. These cells are located in the subendocardial surface of the ventricular walls and are able to rapidly transmit cardiac action potentials from the atrioventricular bundle to the myocardium of the ventricles. This rapid conduction allows coordinated ventricular contraction (ventricular systole) and blood is moved from the right and left ventricles to the pulmonary artery and aorta respectively.