Brand 11/20/08 Cardiac Electrophys

Front 1

decides the RMP. what is cardiac myocyte's RMP?

Back 1

mostly K
myocyte RMP is -90mV

Front 2

cardiac myocyte action potential: describe each phase

Back 2

phase 0: rapid Na influx
phase 1: short K efflux
phase 2: long plateau of Ca influx and some K efflux
phase 3: K efflux to repolarize
phase 4: resting membrane potential

Front 3

differences from skeletal and cardiac action potentials

Back 3

Skeletal - to increase magnitude - recruit more mm fibers, as each AP releases the same amount of Ca.
Heart - to increase magnitude, increase the Ca, by more adrenergic stimulation. Heart also needs extracellular Ca

Front 4

normal path of electrical excitation in the heart

Back 4

SA node -> atrial myocytes -> AV node -> Bundle of His -> R and L Bundles -> Purkinje fibers -> ventricular myocytes

Front 5

determinants of conduction velocity in myocytes and purkinje fibers

Back 5

1. fiber diameter (greatest in purkinje)
2. magnitude of upshoot in AP, phase 0
3. rate of upshoot in AP, phase 0

Front 6

describe the SA node action potential

Back 6

the "I f" , or Na current, occurs after repolarization - this is unique. it is a slow Na influx, which accounts for the pacemaker activity. then, a Ca influx, then a K efflux.

Front 7

ischemia has what effect on K and cardiac myocyte conduction velocity?

Back 7

ischemia -> no ATP -> no Na/K pump -> hyperkalemia -> depolarization, inactive Na channels -> REDUCED CONDUCTION VELOCITY

Front 8

relative rates of pacemaker ability in SA, AV, Purkinje

Back 8

SA: 60-100 beats/min
AV: 50-60
Purkinje: 30-40 (not sufficient)