Rush - Advanced Pharmacology - NSG 531 - Exam 3 Questions
what is the difference between cardiac myocyte action potential and that of the CNS or
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nerve cell action potential is very short
cardiac action potential is much longer
they are longer to have adequate filling time in order to get a good contraction for a reasonable bolus of blood
the only way this can happen is if the action potential is longer
this will also mean that the refractory period will be longer
What are the 5 phases of the non-pacemaker action potential?
0 - depolarization
1 - partial repolarization
2 - plateau
3 - repolarization
4 - resting membrane potential
what happens during phase 0 of the non-pacemaker action potential
depolarization
voltage gated sodium channels are opening up until we get past threshold
what happens during phase 1 of the non-pacemaker action potential
partial repolarization
what happens during phase 2 of the non-pacemaker action potential
plateau
calcium channels open (L-type because they are long)
potassium is still open
potassium out and calcium in - they are opposing each other in voltage giving the plateau
this is when the ventricles are filling
what happens during phase 3 of the non-pacemaker action potential
repolarization
calcium channels are closed
potassium channels are the only thing open taking their positive charge with them making the interior more negative
what happens during phase 4 of the non-pacemaker action potential
resting membrane potential where we are in between action potentials there is no net change in ovltage inside the cell
When does contraction take place?
begins towards the end of repolarization and ends at some point during repolarization
refractory period
during phase 0, 1, 2, and part of phase 3 the cell is refractory to the initiation of new action potentials
many antiarrhythmic drugs increase the Refractory period which reduces myocyte excitability
what are the benefits of the refractory period
limits frequency of cardiac contractions
allows for adequate filling time
prevents sustained contractions
how are pacemaker cells different from non-pacemaker cell
no resting membrane potential - no point where it is flat
there are very few sodium channels in pacemaker - sodium channels are not driving depolarization - calcium is
only 3 phases
comprised of cells within the SA node
generate regular, spontaneous action potentials
what are the phases of pacemaker action potential
0 - rapid depolarization
3 - repolarization
4 - slow depolarization
what happens during phase 0 of the pacemaker action potential
Rapid depolarization
something is coming to open voltage gated calcium channels (L-type) calcium comes rushing in [Show Less]