Purkinje fibers are a vital component in the functioning of the heart, and are thus, vital for our survival. They are a part of the relaying system of electrical signals in the heart, which determines the rate at which the cardiac muscles contract and relax, or in other words, the rate at which the heart 'beats'.
Did You Know?Purkinje fibers were named after the Czechoslovakian scientist who discovered them, Jan Evangelista Purkyně.
Specifically, Purkinje fibers cause the ventricles, the lower two chambers of the heart, to contract in sync. This allows for a coordinated and controlled rhythm of blood circulation. Before learning about Purkinje fibers, a primer on electrical conduction in the heart is necessary. Here's more about the way a heartbeat originates, and the purpose of Purkinje fibers in the process.
Electrical Conduction System of the Heart
► The beating of the heart is controlled by a system of impulse-generating nodes and conducting fibers. The sinoatrial node, commonly known as the SA node, generates the primary impulse and acts as the natural pacemaker for the heart. This node is situated in the inner wall of the right atrium (upper chamber of the heart).
► Impulse generated by the SA node causes the atria to contract, and also activates a second node, the atrioventricular node, known as the AV node.
► The AV node is located, as may be fathomed, between the atria and the ventricles, and is responsible for the generation of the impulse that contracts the ventricles.
► The AV node's impulse is sent approx. 0.12 seconds after the impulse from the SA node. This delay allows for the time taken by the atria to force all the blood into the ventricles. If the AV node generated its impulse along with the SA node, only a very tiny amount of blood would be accepted into the already-contracted ventricles.
► The position and function of the AV node, which is situated in the upper half of the heart but controls the function of the lower half, may appear contradictory, but the gap is filled by a network of fibers known as the bundle of His. The bundle of His carries the impulse from the AV node to the bottom of the heart so that the compression of the ventricles can begin from the bottom. This is necessary, since an upwardly directed contraction is needed to force all the blood into arteries that are situated above the ventricles. A generic 'squeeze' from all sides would cause some blood to remain in the ventricles.
► The bundle of His (incidentally, named after Wilhelm His, Jr., the scientist who discovered it) bifurcates into the left and right bundle branches, each leading into the respective ventricle.
► The bundle branches lead to the Purkinje fibers, which carry out the contraction of the ventricular muscles, approx. 0.15 seconds after the atria have contracted. It takes less than 0.05 seconds for the impulse to travel from the bundle of His to the Purkinje fibers. This contraction generates the force necessary to force the blood out of the ventricles.
► Purkinje fibers are present in the inner walls of both ventricles. This location allows the fibers to orchestrate a complete contraction with minimal fuss. Even though the two ventricles send the blood to different destinations (the right one sends the blood to the lungs to be purified, and the left one sends it into the aorta to be distributed to the rest of the body), both contract at the same time, so the Purkinje fibers on both sides are activated at the same time.
► Purkinje fibers contain a special type of cardiac muscles that make them the most efficient and quickest conductors of impulses in the cardiac system. The histology of these muscles reveals that they have thinner muscle fibers with fewer muscle strands than normal cardiac cells, which makes them appear lighter than other cells in a stained slide.