287 FA PACEMAKER ACTION POTENTIAL

PACEMAKER

[@JJAngleton]

Hi, I actually luv your lectures, though that time I'd explain it different: Pacemaker cellls (SA/AV node) are differing from others due to their different mechanism how to reach threshold: Myocardial cells are taken up to threshold by voltage gated sodium channels, while pacemaker cells have leaky sodium channels that permanently taking the membrane potential up to threshold at which voltage gated calcium and potassium channels are opening.

[@JJAngleton]

The latter ones do have a less negative membrane potential because pacemaker cells are not only freely permeable to potassium (therefore are near the Nernst potential of Potassium at -90mV), though in a small amount to Sodium as well. Nernst potential is the equilibrium between electrical and concentration gradient of an Ion and hence it differs between K+ and Na+

[@JJAngleton]

Calcium dependent depolarisation is slower then sodium dependent, plus pacemaker cells have a rather long plateau phase in the action potential while voltage gated calcium and potassium channels are opened simultaneously before they repolarise due to potassium efflux. In that moment, the membrane potential rushes near the K+ equilibrium potential, until it is due to the leaky Sodium channels taken up to threshold and opens again the voltage gated calcium and K+ channels.

[@HxAlabdulla]

medimarc ,,, I totally got lost with you haha sorry you look genius anyway I just wonder why would SA node have a long plateau phase ?? did I misunderstand you please tell me why cues I'm confused

[@JJAngleton]

I did a mistake; Of course, SA & AV nodal cell do actually have a shorter plateau phase, though a relatively slow depolarisation due to the slower Ca++ influx & the less negative resting membrane potential. Myocardial cells instead have a long plateau due while Ca++ and K+ are opened parallel and neutralise each other. Sorry for the confusing explanation.