o Although rhythm can be altered by the ANS Coordinated heartbeat is a function

O although rhythm can be altered by the ans

This preview shows page 40 - 42 out of 61 pages.

oAlthough rhythm can be altered by the ANSCoordinated heartbeat is a function of :oGap Junctions being present Cardiac Pacemaker Cells – initiate action potential oAction Potential 3 parts:Pacemaker potential – K+ channels are closed, but slow Na+ channels are open, causing interior to become more positiveDepolarization– Ca2+ channels open (-40mV) allowing huge influx of Ca2+,leading to rising phase of action potentialRepolarization – Due to Ca2+ channels inactivating and K+ channels open, efflux of K+ and cells go back to most negative voltage oSequence of excitation:Components:oSA node (Sinoatrial)-pacemaker that generates impulses (depolarizes on its own)Depolarizes faster than rest of the heartGenerates impulses at 75x/min (sinus rhythm)Inherent rate of roughly 100 x/min (this is tempered down to 75 by extrinsic factors)Impulse spreads across atriathrough inferior interatrial septum AV nodeoAV node (atrioventricular) – impulses pause 0.1 sec at this nodeLocated in inferior interatrial septumDelays impulses by 0.1 sec to allow atrial contraction prior to ventricular contractions
Background image
oBecause fibers are smaller in diameter and have fewer gap junctions Inherent rate of 50x/min in absence of SA nodeinput oSA node is usually nott absent however so the 75 wins over 50 from AV You can survive at 50 howeveroAV bundle– conducts impulses to the bundle branchesIn superior interventricular septum Only electrical connection between atria and ventricles oAtria and Ventricles are not connected via gap junctionsRate of 30x/min in absence of AV node input (but you cannot survive at 30)oBundle Branches– conducts impulses through interventricular septumRight and Left bundle branches oSubendocardial conducting network (Purkinje Fibers)– depolarizes the contractile cells of both ventriclesComplete pathway through interventricular septum into apex and ventricular walls More elaborate on left than right side of heartRate of 30x/min in absence of AVoModification of Basic RhythmModified by ANS via cardiac centers in medulla oblongataCardioacceleratory center: signals go throughsympathetic trunk to increase both rate and forceoStimulates SA and AV nodes, heart muscles and coronary arteries oONLY IN VENTRICLES THO! Not atrial oIncreases via cardiac sympathetic nerves Cardioinhibitory center: goes through parasympathetic nervous system via vagus nerveto decrease rateoInhibits SA and AV nodes via vagus nerve Action Potential of Contractile cells:oDepolarization – Na+ influx through fast gated Na+ channels oPlateau phase – due to Ca2+ influx through slow Ca2+ channels, keeps cell depolarized because most k+ channels are closed oRepolarization– due to Ca2+ channels inactivating and K+ channels opening, allows K+ efflux bringing membrane potential back to resting phase oECG and/or EKG(EKG is German lol)(electrocardiogram) is a graphic recording of electrical waves of cardiac cycle :P wave (beginning) (SA node – initiates atrial depolarization)o
Background image
Image of page 42

You've reached the end of your free preview.

Want to read all 61 pages?

  • Spring '16

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture