BIOL 1119 Lecture 5: Circulatory System- The heart Lecture 5
19 Aug 2016
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Document Summary
Electrical and contractile activity of the heart. Structure of the cardiac muscle: the heart is mostly muscle; striated but different from skeletal in other ways, cardiocytes are short, branches cells, sarcoplasmic reticulum, large t-tubles. Admit ca2+ into cardiocyte to activate muscle contraction. Intercalated discs: join cardiocytes end to end interdigitating folds: increase surface area mechanical junctions tightly join myocytes electrical junctions: gap junctions allow ions to flow between cardiocytes, enable coordinated contraction of network of cardiocytes. Properties myogenic: heartbeat signal for contraction originates within heart cardiocytes (heart muscle cells or cardiac myocytes or just myocytes) are autorhythmic: regular, spontaneous depolarization. The heartbeat is coordinated by a cardiac conduction system composed of an internal pacemaker and nervelike conduction pathways through the myocardium. Sinoatrial (sa) node: modified cardiocytes in right atrium, initiates and sets heartbeat; the pacemaker. Av bundle: pathway for signals from av node. Right and left bundle branches: divisions of av bundle that enter interventricular septum and descend towards apex.
