o Arranged in tightly bound layers that encircle blood filled chambers

O arranged in tightly bound layers that encircle

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o Arranged in tightly bound layers that encircle blood filled chambers contraction they come together. Endothelium : thin cells found in the inner surface of cardiac chambers & blood vessels. Interventricular septum: muscular wall separating ventricles AV values: found between atrium and ventricles o Right AV tricuspid valve and Left AV bicuspid valve or mitral valve Opening of valves due to passive pressure differences Valves are fastened to ( papillary muscles ) by fibrous strands ( chordae tendineae ): allow for valves to not open. Semilunar valves Pulmonary valves (right ventricle into pulmonary trunk) & aortic valves (left ventricle in aorta). Valves when open have little resistance to flow. Small pressure differences large flows. Atrial contraction pumps little blood back to veins b/c atrial contraction constricts sites of entry into atria. Cardiac muscle/Innervation/ Blood Supply Cardiac muscle is similar to skeletal muscle exc itable tissue that converts chemical E in ATP into force (AP’ s occur) Conducting system : 1% of cardiac cells do not do contraction o Electrical contact with cardiac muscle cells occurs via gap junctions (helps spread AP fast) Heart receives rich sympathetic/parasympathetic nerve fibers in Vagus nerve Sympathetic preganglionic fibers innervate heart, release NE (beta-adrenergic receptor) Parasympathetic: terminate on spatial cells in atria, release Ach (muscularic receptors) Coronary arteries: supply myocardium and blood flowing through them is coronary blood flow; receive blood from atria. Cardiac veins drain into coronary sinus which dumps into right atrium Wednesday 10/4/17 Lecture 18: Heartbeat Coordination and Mechanical Events of the Heart 12.4 Heartbeat Coordination/ Sequence of Excitation Initial depolarization via plasma membrane and gap junctions arises in a small group of conducting cells called the SA node, located in the right atrium near superior vena cava. Space between both has lubricant fluid F= P/R
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17 Process: 1. SA node: pacemaker of heart, depolarization of generates AP leads to depolarization of all other cardiac cells. It first will spread through muscle cells of atria 2. AV node : link between atrial depolarization and ventricular depolarization, base of right atrium. i. AP’s through here are VERY SLOW to allow for atrial contractio n to be completed before ventricular excitation. 3. Goes through interventricular septum (after excit.) Bundle of His/ AV bundle (only electrical attraction between atria and ventricles) right/left bundle branches (separate at apex of heart, enter heart walls) 4. Purkinje fibers: large diameter; rapid conducting cells connected by low resistance gap junctions i. Will allow for fast AP to myocytes in ventricles (blood will move upward toward exit valves) Heart rate: determined by discharge rate of SA note, number of times heart will contract. Internodal pathways: AP goes fast between SA node and AV node. Myocardial Cell Action Potential Process Normally, Na depolarizes, at rest K+ leaks, inactivation period occurs due to Na+.
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