Flashcards in cardiac electrophysiology Deck (23):
types of myocardial cells
pacemaker or non pacemaker
slow and automatic depolarizing to threshold- all or nothing. DO NOT stop at resting. Autorythmic at SA or AV node
non pacemaker cells
contration and force development. AP when stimulated.
pacemakers in the heart
SA node, AV node, His/Purkinje fibers
action potential for pacemaker cells
three phases: Phase 4 depolarization, depolarization/action potential, depolarization to rest
phase 4 depolarization
membrane potential hits threshold. First, decreased K outflow. Then funny current- slow NA in, then Ca influx- raise membrane potential
hit threshold, voltage L type calcium channels open, shoot membrane potential up
repolarization to rest
voltage gated K open, repolarizing
how is HR modulated?
autonomic innervation of AV/SA nodes
slow down HR. Vagus nerve releases acetylcholine. Slower K closing leads to hyper polarization. decreased funny leads to reduced phase 4 slope, decreased Ica influx leads to late threshold.
Increase rate and force of contraction. cardiac plexus releases norepinephrine to AV, SA , and myofibrils. Increased funny current in nodes, increased Ca influx in myocardial cells, more negative threshold. more ATPase activity in myocardium
non pacemaker cell AP
5 phages, including a plateau which allows time for filling. Resting potential at -90, requires signal.
refractory period in non pacemaker cells
effective/absolute: 0-3 phases, requires relaxation before refuel. no tetanus possible.
phases of non pacemaker AP
0- Na influx voltage gated
1- Na inactivation, K open- slight repolarization
2- plateau- increased Ca in with slow K outflow
3- repolarization, Ca closes and K out
4- resting potential
sequence of AP through heart
SA node> atrial muscle cell to cell (slow fibers, Atria contract) > AV node > AV junctional fibers (slow)> Fibers exit AV, enter ventricle at His> His divides down septum > bundle branches> perking fibers> myocardium
direction of repolarization
upper right atrium, 60-100
septum, 40-50 beats
his perkije fibers
conducting network in ventricles. 20-30 beats per min
normal HR for pacemaker potential
force of contraction- increased funny current in sympathetic.
heart rate- lower threshold sympathetic