Electrical Activity of the Heart-the pacemaker= SA node begins AP-conduction of the system of the heart-spread of excitation through the heart muscle-ionic basis of electrical activity in the heart-electrical activity in cardiac contractile cells-recording the electrical activity of the heart with an electrocardiogram How does pacemaker work? Autorhythmic cells- ability to generate own rhythm Sinoatrial node (SA node) 1. generates the rhythm 2. heart's pacemaker Conductile System 1. pace maker cells-spontaneously depolarizing membrane potentials to generate action potentials 2. conduction fibers- rapidly conduct action potentials initiated by pacemaker cells to myocardium-conduction velocity= fast (4m/s)-skeletal muscle fibers= slower than cardiac conduction fibers (.4 m/s) Pacemaker cells of myocardium 1. pacemaker cells-SA node (pacemaker of the heart, set the rhythm)-AV node *then go into ventricle to. ... 2. conduction fibers-internodal pathways-bundle of His-Purkinje fibers (main contraction) Autorhythmic Cells Location Firing Rate at Rest SA Node (sets rhythm) 70-80 APs/min* AV Node 40-60 APs/min (not optimal, but not death) Bundle of His 20-40 APs/min Purkinje Fibers 20-40 APs/min • Fastest depolarizing cells control other cells • Fastest cells = pacemaker - set rate for rest of heart * action potentials per minute (tonic control by parasympathetic nervous system) otherwise ~ 100 APs/min-parasympathetic has a large impact *if SA node not working, alternative cells activate: it is not optimal, but it allows you not to die *ion movement across gap junctions is the electrical current in the heart
both atria contract at the same time AV node contracts slower so that all the blood can leave the atria Spread of Excitation 1. Interatrial pathway-SA Node (pacemaker)-Rapid Conduction-simultaneous contraction of right and left atria-atria contacts before the ventricles 2. Internodal pathway SA Node--> AV Node (AV node delay= .1 s) *delay because blood must be emptied from atrias 3. AV Node transmission-ONLY pathway from atria to ventricles-slow conduction 4. Ventricular excitation-DOWN bundles of His (fast: 2m/s)
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