ch. 19 pacemaker Flashcards
1
Q
19.4b Pacemaker Physiology
SA node fires spontaneously at
A
regular intervals
2
Q
pacemaker mechanism
SA node does not have a stable
A
resting membrane potential
3
Q
pacemaker mechanism
starts at -60mV and drifts upward due to slow
A
Na+ inflow this gradual depolarization is the pacemaker potential (prepotential)
4
Q
pacemaker mechanism
When it reaches threshold of -40mV voltage gated Ca2+ and Na+ channels
A
Open
Faster depolarization occurs peaking at 0mV
5
Q
pacemaker mechanism
K+ channels then open and K+ leaves the
A
Cell causing repolarization
Once K+ channels close pacemaker potential starts over
6
Q
SA node physiology
When SA node fires it sets off
A
Heartbeat
As the internal pacemaker it typically fires every 0.8 sec setting the resting rate at 75 bpm
