Chapter 2: Electrophysiology

muscle cells
pacemaker cells
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polarized cell (resting state)-inside of cell is negative -no electrical activity occurring (straight line on ECG)depolarization (stimulated state)-electrical stimulation of cardiac cells causes K+ to exit cell and Na+ to enter cells -inside becomes positive -muscle contraction followsrepolarized cell (recovery state)-sodium potassium pump activated to transport Na+ out of the cell and K+ back into cell -inside of cell returns to resting state (negative charge)depolarization and depolarizationwavelength on the ECG correlate with _____ and _____sinoatrial node (SA node)-located in the *right atrium* -contains *pacemaker cells* which discharge impulses at *60-100 beats / minute* -called *pacemaker of the heart* because its firing rate is higher than that off other pace maker sitesinteratrial tract / Bachmann's Bundle-one conduction tract with conducts impulse from *SA node to left atrium*internal tracts-three conduction thats, which conduct impulse from *SA node through right atrium to AV node*atrioventricular node (AV node)-located in *lower right upper atrium* near intertribal septum* -only normal conduction pathway between *atria and ventricles*the atrioventricular node (AV node) *slows conduction* of electrical impulse through the AV node to allow time for atrial contraction / *atrial kick*; delay in AV node represented on ECG as flat line of *PR interval*what is the primary function of the AV node?atrioventricular node (AV node)-serves as *backup pacemaker* at firing rate of *40-60 beats / minute* -*blocks rapid atrial impulses* from being conducted to ventricles, protecting ventricles from dangerously fast ratesBundle of His-connects *AV node to bundle branches*Bundle branches-consists of right and left branch, which *conducts electrical impulses to the right and left ventricle*Purkinje Fibers-network of fibers located at *end of bundle branches* which conduct electrical impulses to *ventricular myocardium* -ventricles are capable of serving as a backup pacemaker at firing rate of *20-40* beats / minute (sometimes less)P wave QRS complex T wave (U wave is sometimes present)the heart's electrical activity is represented on the EKG tracing by 3 basic waveforms... what are they?PQRSTa cardiac cycle consists of one heart beat or one _____ sequence; one cycle represent atria contraction and relaxation followed by ventricular contraction and relaxation; this basic cycle repeats itselfR-R intervalregularity of a cardiac *rhythm* can be measured from one heart beat to the next by the _____ _____isoelectric linebetween cardiac cycles the EKG records a *straight line* or a baseline... what is this called?positive deflectionany waveform *above* the baseline is considered _____ _____negative deflectionany waveform *below* the baseline is considered _____ _____biphasic deflectiona waveform that is *both above and below* the baseline is considered a _____ _____two doesan EKG tracing provides a view of the hearts electrical activity between _____ _____ (a positive and a negative)positive deflectioncurrent flowing toward a positive poe produces a _____ _____negative deflectioncurrent flowing toward a negative pole produced a _____ _____biphasic deflectioncurrent flowing away from both poles will produce a _____ _____; they may be equally positive and negative, more positive than negative, or more negative than positiverefractory periodthere is a period of time during the cardiac cycle when cardiac cells may be *unable to respond* to a stimulus; to os divided into 2 phases... what is this called?absolute refractory period and relative refractory periodwhat are the 2 refractory phases?absolute refractory period-cardiac cells have not depolarized to their threshold potential and are *unable to respond to a stimulus* -period extends from *onset of QRS complex to peak of T wave*relative refractory period-cardiac cells have depolarized sufficiently to respond to a *strong stimulus* -period extends from *peak of T wave to end of T wave* -called *vulnerable period* of depolarization since a strong stimulus may take possession as pacemaker of the heart0.04 seconds 1/2 box = 0.02 secondseach small square of an EKG measures how many seconds?