Heartbeats - Heartbeats Summary: Two general classes of...

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H e a r t b e a t s
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Summary: Two general classes of cardiac muscle cells are involved in the normal heartbeat : contractile cells and cells of the conducting system. Cardiac muscle cells have a long refractory period, so rapid stimulation produces isolated rather than tetanic contractions. The conducting system is composed of the sinoatrial node, the atrioventricular node, and conducting cells. This system initiates and distributes electrical impulses within the heart. Nodal cells establish the rate of cardiac contraction, and conducting cells distribute the contractile stimulus from node to node (along internodal pathways) and from the nodes to the ventricular myocardium. Unlike skeletal muscle, cardiac muscle contracts without neural or hormonal stimulation. Pacemaker cells in the sinoatrial (SA) node (cardiac pacemaker) normally establish the rate of contraction. From the SA node, the stimulus travels to the atrioventricular (AV) node , then to the AV bundle , which
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This note was uploaded on 07/15/2011 for the course SCIENCE 232 taught by Professor Martin during the Spring '11 term at UCLA.

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Heartbeats - Heartbeats Summary: Two general classes of...

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