III8 - III Heart Physiology Internal Conduction(Stimulation System of the Heart A General Properties of Conduction 1 2 3 B heart can beat

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Heart Physiology III. Internal Conduction (Stimulation) System of the Heart A. General Properties of Conduction 1. heart can beat rhythmically without nervous input 2. nodal system (cardiac conduction system) - special autorhythmic cells of heart that initiate impulses for wave-like contraction of entire heart (no nervous stimulation needed for these) 3. gap junctions - electrically couple all cardiac muscle cells so that depolarization sweeps across heart in sequential fashion from atria to ventricles B. "Pacemaker" Features of Autorhythmic Cells 1. pacemaker potentials - "autorhythmic cells" of heart muscle create action potentials in rhythmic fashion; this is due to unstable resting potentials which slowly drift back toward threshold voltage after repolarization from a previous cycle. Theoretical Mechanism of Pacemaker Potential: a. K + leak channels allow K + OUT of the cell more slowly than in skeletal muscle b. Na + slowly leaks into cell, causing membrane potential to slowly drift up to the threshold to trigger Ca ++ influx from outside (-40 mV) c.
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This note was uploaded on 01/29/2012 for the course SCIE SYG2000 taught by Professor Bernhardt during the Fall '10 term at Broward College.

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III8 - III Heart Physiology Internal Conduction(Stimulation System of the Heart A General Properties of Conduction 1 2 3 B heart can beat

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