Biol 216 9 Circulatory System 97-128.pdf

Biol 216 9 Circulatory System 97-128.pdf - Sinoatrial(SA...

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5/24/17 1 Sinoatrial (SA) node Cells in the SA node spontaneously depolarize, resulting in contraction, approximately 100 times per minute. This rate is constantly modified by the activity of sympatheticand parasympathetic nerve fibers, so that the average resting cardiac rate in adult humans is about 70 beats per minute. 5/24/17 97 Sinoatrial Node Atrioventricular Node Bundle of His Right Bundle Branch Left Bundle Branch Purkinje Fibers http://www.nhlbi.nih.gov/health/dci/Diseases/hhw/hhw_electrical.html http://www.nhlbi.nih.gov/health/health-topics/topics/hhw/electrical.html 5/24/17 98
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5/24/17 2 Heart Electrical Activity Pacemaker cells insinoatrial node spontaneously generate action potentials. Potentials spread rapidly through the atria , and reach a region calledthe AV node (atrial ventricular node ) Slow transmissionthrough the AV node Then to large connecting fibers ( Bundle of His) withleft and right bundle branches descending from the AV node in the middle of the heart. Rapid spread of action potential These connect withPurkinje fibers that gointo the ventricular wall anddeliver the action potential very rapidly. 5/24/17 99 Heart Electrical Activity There is no electrical connection between the muscle cells of the atria and the muscle cells of the ventricles. There is (just connective tissue between them). The only wayto get from the atria to the ventricle are through some conducting fibers that have small diameters. What effect will the small diameter have on the speed of the action potential? 5/24/17 100
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5/24/17 3 Heart Electrical Activity Why would you want the action potential to go though the atria to the ventricles slowly? 5/24/17 101 Heart Electrical Activity Answer: because you don’t want the atria and ventricles to pump at the same time. You want the ventricle to contract and pump the blood out and then you want the ventricle to fill up withblood. That takes some time, and then you want the atria to contract. Thus there is a delay between the contraction between the atria and the ventricle. The atria contract, filling upthe ventricle, then the ventricle contracts, pumping out the blood, blood flows in, atria contract, then there is a little delay, then the ventricles contract. 5/24/17 102
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5/24/17 4 Summary Slide: conduction 1. Signals from SA node spread thru atria 2. Signals are delayed at AV node 3. Bundle branches pass signals to heart apex 4. Signals spread throughout ventricles 5/24/17 103
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