oArranged 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 oRight 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—excitable tissue that converts chemical E in ATP into force (AP’s occur) ▪Conducting system: 1% of cardiac cells do not do contraction oElectrical 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
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 contraction 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+.