BIO 365R Lecture17--heart_muscle%20

BIO 365R Lecture17--heart_muscle%20 - left ventricle right...

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Unformatted text preview: left ventricle right ventricle right atrium left atrium to body from lung from body to lung Representational diagram of the four chambers of the heart O 2 CO 2 Vena cava Venous return Aorta Arterial outfow Vena cava Venous return Aorta Arterial outfow left atrium left ventricle right atrium right ventricle 1) SA node depolarizes and generates action potentials that spread through right atrium. 2) Atrial action potentials reach AV node. AV node depolarizes and generates action potentials 3) Action potentials spread down right and left fibers that run along ventricular walls. Ventricular fibers begin to depolarize throughout both ventricles. 4) Ventricular fibers depolarize, generate action potentials and cause ventricles to contract. bundle of His SA node AV node Coordination of SA and AV conducting systems The cells of the cardiac conduction system (SA & AV nodes, bundles of His, Purkinje Fbers) are muscle-derived but lack myosin etc and do not contract . The SA node Fres at ~70 times/ minute. The AV node Fres ~50 times/ minute. So the SA node drives the AV node . This is because the SA node has more H channels than the AV node. The AV node has a special region that delays fring an AP for about 100 millseconds to allow the atrium to complete its contraction, otherwise the atria and ventricles would contract at the same time. The delay is because this region of the AV node has: 1) fewer gap junctions; 2) low membrane resistance, high internal resistance (small length constant); 3) fewer Na + channels....
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BIO 365R Lecture17--heart_muscle%20 - left ventricle right...

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