BIOL 305 : BIO 305 quiz 3
Document Summary
Heart: you have 2. 8 billion beats most mammals have 1. 5 billion beats. Heart - position: located in mediastinum of thoracic cavity medial position, but rotated and tipped to left, enclosed within pericardial cavity, double-walled serous membranous sac, parietal pericardium tough, fibrous, visceral pericardium applied directly to surface of heart muscle (= epicardium) The cardiac cycle: a heartbeast is a sequence of actions - basically, systole (contraction) and diastole (relaxation) form a cardiac cycle, three steps, starting from complete relaxation of atria and ventricles: 1. atrial systole both atria contract and force blood through av valves into ventricles => Cardiac muscle: cardiac muscle cells connected to one another by intercalated discs (gap junctions, cardiac muscle cells autorhythmic gap junctions allow coordination of contraction and relaxation, allows rapid communication of signals across myocardium. Cardiac conduction system: non-contractile cells throughout the heart, self-excitatory, produce and conduct their own signals, largely autonomous of central nervous system rate regulated, but sequence of events innate.
