These fibers extend out to all areas of the two ventricles and since they are further enlarged, the speed of the impulse conduction is also additionally increased. An important fact about the fibers that make up the AV bundle is that they are large in diameter and therefore the impulse speed increases so it is conducted very rapidly down them.Ībout halfway down the interventricular septum the “bundle branches” themselves begin to branch off into enlarged conduction fibers called Purkinje fibers. The AV bundle divides into two lines of transmission just below the AV node and these conduct the impulse down the length of the interventricular septum. This is an extremely important phenomenon because the delay in the transmission from atria to ventricles allows time for the atria to completely depolarize and contract, thus emptying their contents into the still fully relaxed ventricles.įrom the AV node, the impulse travels down the atrioventricular bundle. This is due to the extremely small diameter of the conducting fibers. As the impulse is conducted through the AV node, its speed is reduced. This group of fibers is the only conduction pathway between the atria and ventricles. The AV node is located in the floor of the right atrium next to the interatrial septum. The impulse does not however pass directly to the ventricles.Īs the atria depolarize, the impulse is picked up by another group of specialized muscle fibers called the atrioventricular node. Impulses from the SA node are then conducted across the atria from right to left. When both the right and left atria are completely depolarized, they contract simultaneously. This is also why the SA node is said to be the “ pacemaker ” of the heart This means that the SA node is said to be “ self exciting ”. The specialized muscle fibers that make up this structure are unique in that they can continually and rhythmically send impulses (signals to contract) without any stimulation from the nervous system. The sinoatrial node The SA node is located in the wall of the right atrium near the S.V.C. The Purkinje fibers The cardiac muscle fibers that compose these structures are specialized for impulse conduction ,rather than the normal specialization of muscle fibers for contraction. The atrioventricular bundle ( AV bundle) 4. The Cardiac Conduction System The impulse conduction system of the heart consists of four structures: 1. Conducting System Network of specialized tissue that stimulates contraction Modified cardiac myocytes The heart can contract without any innervation
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