electrical activity short Flashcards
Resting membrane potential of ventricular myocytes (Em)
-90mV
Equilibrium/Nernst potential Ek/na
The membrane potential necessary to stop an ion diffusing down it sconcentration gradient
action potential
when membrane potential depolarizes then repolarizes back to resting state, this happens in a wave of electrical discharge that travels along the membrane of an excitable cell
Absolute refractory period (ERP)
phase 0,1,2 and part of 3 - cell cannot be excited by a new action potential (h gates still closed)
benefit of ERP
limits the frequency of ap’s and therefore contractions that the heart can generate so has time to fill and eject blood. stops tetanic contractions
relative refractory period
at end of ERP, suprathreshold depoalrization stimuli can elicit ap’s. Will have a decreased phase 0 slope
sinoatrial node
in posterior wall of right atrium, primary pacemaker site as highest rate
overdrive suppression
intrinsic activity of secondary pacemakers suprresssed and they are hyperpolarzied
does ecg measure absolute voltage?
no, measures voltage changes from isoelectric baseline
verticle and horizontal values on ecg
1mV/cm, 25mm/sec (1 small .04 sec, 1 big .2 second, 5 big is 1 second)
Q-Tc calculation
Q-Tc = QT/ square root of RR
dromotrophy
conduction velocity, increased by symp, decreased by parasymp
threshold
level of depolarization at which a self propagating action potential is generated
excitability
Slope and conduction velocity of phase 0. As ap’s are initiated later in the relative refractory period of the preceding excitation you get a steeper phase 0 slope, most excitable when resting membrane potenital reached first and phase 0 slope able to return to its steepest
irritability
diminished potential between resting and threshold, as irritability increases, depolerization is easier but phase 0 has reduced conduction velocity and gradient
