phys-cardiovascular notes 2 - Electrical Activity of the...

phys-cardiovascular notes 2
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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
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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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