PHYL2001 Final: PHYL2001 Revision The Heartbeat 2
Document Summary
Ap starts at sinoatrial node (sa node) Ap enter boh (bundle of his) (rapid) Ventricles depolarise from endocardium to epicardium from apex to base. Sa node is the fastest pacemaker potential (the normal pacemeaker) Ectopic heartbeat = a beat generated outside the normal pacemaker. Fastest cells in sa node (highest and normal pacemaker rate), driving the other cells to. Which is slower than sa nodes in isolation. But neural input is not required to generate a heart beat. Neural input can modify it = chronotropic. Eg. adrenaline, na -> on beta adrenergic receptors. Eg. ach -> on m-cholinergic muscarinic receptors. @ rest= parasympathetic tone present in heart = natural rhythm of heart. Resting hr = 70bpm (pns chronically active, slowing the hr = endogenous rate) The heart itself beats 90-100bpm but pns slows it down. Increase hr by removing pns tone and activating sns and releasing a/na, acting on beta receptors.
