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Contraction of heart muscle cells occurs by the action potential membransel delivered throughout the heart muscle. The heart will contract rhythmically, as a result of electrical impulses generated by the heart itself: an ability called "autorhytmicity". This property is owned by the specialized cells of heart muscle. There are two specific types of heart muscle cells, namely: the contractile cells and cell otoritmik. Tues contractile perform mechanical work, ie pump and otoritmik cells specialize and menghatarkan trigger action potentials that are responsible for contraction of worker cells.In contrast to nerve cells and skeletal muscle cells that have a stable resting membrane potential. Special cells in the heart does not have a membrane resting potential. These cells show the activity of "pacemaker" (pacemakers), a slow depolarization followed by action potentials when the membrane potential reaches a fixed threshold. Thus, action potential timbulah periodically that will spread throughout the heart and causes the heart beat regularly without the stimulation through the nerves. Mechanism underlying slow depolarization in cardiac cells specialized conduction still not known with certainty. At the heart otoritmik cells, membrane potential is not settled between the action potentials. After an action potential, membrane depolarization or slow run to the threshold shift due to inaktivitasi saluranK +. at the same time when the little K + out of cells due to pressure drop K + and Na +, the permeability does not change, continues to leak into the cell. As a result, the inside is slowly becoming less negative membrane that is experiencing a gradual depolarization toward the threshold. Once the threshold is reached, and Ca + + channels open, Ca + + influx occurs rapidly, causing rising phase of the potential aksispontan. Phase of K + channels. Inaktivitasi these channels after an action potential rise over the next slow depolarization reaches the threshold. Heart cells are capable of experiencing otoritmisitas found at the following locations:1) sino atrial node (SA), a special small area in the wall of the right atrium near the superior vena cava hole.2) atrio ventricular node (AV), a small beam of heart muscle cells specialized in the bottom of the right atrium near the septum, just above the linkage atrium and ventricle.3) File HIS (file atrio ventricular), a pathway specialized cells derived from the AV node and into the inter-ventricular septum, where the file is branched to form a file kana and the left that runs down through the septum, encircling the end of the ventricular chamber and re- the atrium along the outside wall.4) Purkinje fibers, fine fibers that run from the terminal HIS files and spread throughout the ventricular myocardium as the branches of trees.
A variety of specialized conduction cells have a spontaneous impulse formation rates are different. SA node has the ability to form spontaneous impulse fastest. These impulses spread around the heart and also determines the basic rhythm of the heart, so that in normal circumstances, simpuls SA acts as a trigger of heart. Other special conductive tissues can not trigger an action potential intrinsic because these cells are activated in advance by action potentials originating from the SA node, before these cells are able to reach the threshold of arousal itself. The order of the ability of action potential formation of a variety of specialized cardiac conduction structure is:1) SA node (pacemaker normal): 60-80 beats per minute2) The AV node: 40-60 beats per minute3) File HIS and Purkinje fibers: 20-40 beats per minute
The spread of cardiac excitation is coordinated to ensure efficient pumping. This deployment dimulain in the presence of spontaneous action potentials in the SA node. Action potential running quickly spread in both atria. The spread of the impulse is facilitated by two conductive paths, namely paths antaratrium and between nodes. With the lines between the nodes, the impulse then spreads to the AV file, which is the only point where the action potential can spread from the atria into the ventricles. However, because the special arrangement of the conductor system from the atrium into the ventricle, there is a deceleration of more than 1 / 10 sec between the way the heart impulses from the atria into the ventricles. The cause of the slowdown is due to the thinness of impulse delivery fiber in this area and link the difference in low concentrations. Links difference is itself a mechanism of communication between cells that facilitate the conduction of impulses. This allows atrial contraction precedes ventricular pump blood to the ventricles before the ventricular contraction is very strong. Thus, the atrium works as a pump primer for the ventricles, and ventricles then provide the primary power source for the movement of blood through the vascular system. From the AV node. Action potential to spread rapidly throughout the ventricles, facilitated by specialized ventricular conduction system consisting of a bundle of His and Purkinje fibers.
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