The intrinsic ability of cardiac muscle to generate action potentials (APs) rhythmically is achieved by the normal pace maker, the sino-atrial node(S-A node). The S-A node is part of the special excitatory and conductive system of cardiac muscle. With the help of a diagram, describe this conductive system how the AP spreads throughout the muscle.
The special excitatory and conductive system of cardiac muscle is responsible for spreading action potentials (APs) throughout the muscle and coordinating its rhythmic contractions. The main components of this system include the sino-atrial node (S-A node), atrioventricular node (A-V node), Bundle of His, and Purkinje fibers.
1. Sino-Atrial Node (S-A Node): The S-A node is located in the upper part of the right atrium near the opening of the superior vena cava. It acts as the primary pacemaker of the heart, generating electrical impulses that initiate each heartbeat. These impulses spread throughout the atria, causing muscle contraction.
2. Atrioventricular Node (A-V Node): The A-V node is located in the lower part of the right atrium, near the interatrial septum. It acts as a bridge between the atria and ventricles, slowing down the electrical impulses from the S-A node before transmitting them to the ventricles. This delay allows for atrial contraction to be completed before ventricular contraction begins.
3. Bundle of His: The Bundle of His is a collection of specialized conductive fibers that originate from the A-V node and travel through the interventricular septum (wall between the ventricles). It splits into branches, known as the left and right bundle branches, which further divide into smaller Purkinje fibers.
4. Purkinje Fibers: The Purkinje fibers are a network of specialized cardiac muscle fibers that distribute the electrical impulses rapidly and uniformly to the ventricles. They extend from the Bundle of His and spread throughout the ventricular walls. This rapid conduction ensures coordinated ventricular contraction.
Diagram:
Here is a simplified diagram representing the conductive system in cardiac muscle:
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S-A Node -> Atrial muscle -> A-V Node -> Bundle of His -> Purkinje Fibers -> Ventricular muscle
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In this diagram, electrical impulses are generated at the S-A node (depicted as a small structure in the right atrium) and spread through the atrial muscle causing atrial contraction. The impulses then pass through the A-V node (depicted as a structure near the interatrial septum) and enter the Bundle of His (depicted as a bundle of fibers traveling through the interventricular septum). From the Bundle of His, the impulses travel down the left and right bundle branches to the Purkinje fibers (depicted as a network of fibers) which distribute the impulses throughout the ventricular muscle, resulting in ventricular contraction.