Cardiac Action Potential Flashcards
Why does the heart have two different action potentials?
The myocytes have a separate AP than the pacemaker cells of the heart
Why is there a plateau in the cardiac AP of myocytes?
Voltage gates Ca channels open, small Na influx via same Ca channels and K conductance is decreased
When does systole and diastole occur on the cardiac AP?
Systole is seen during AP generation (upstroke) and diastole is seen at resting membrane potential
What part of the pacemaker cells action potential can be changed in order to increase heart rate?
Phase four can be sped up by an increase in conductance to Na ion (this is where drugs work)
What does the notch on the myocyte AP represent?
Na gate closes, K efflux but Ca channels open which causes the cell from completely repolarizing
What conducts the AP from the atria to the ventricle?
A-V bundle (delayed from decrease in gap junctions)
What carries the AP from the right atria to the left atria?
Internodal fibers course through the atria from right to left
Why is there a delay at the A-V node?
In order to prevent the atria and ventricles from pumping at the same time
What two factors prevent an AP from traveling from ventricle to atria?
A-V bundle is specialized one way conduction
Atria are electrically insulated from the ventricle by fibrous tissue
Why is it beneficial to depolarize from epi to endocardium and depolarize from endo to epicardium?
Prevents tetany of the cardiac muscle
Since the sarcoplasmic reticulum is less developed in cardiac myocytes, how do these cells obtain Ca for contraction?
Enhanced t-tubule system, bring more ECF to cardiac myofibrils, this means more Ca
In a healthy heart, why doesn’t tetany occur?
The mechanical event ends prior to the end of the electrical event
How does the parasympathetic nervous system impact the rate of the heart?
Ach is released by the vagus nerve, Ach increases VG K channel which hyperpolarizes RMP (decreased HR)
What four factors are enhanced by SNS activation of the myocytes?
Increase SA node rhythm
Increased excitability of AV fibers (faster transmission)
Increased force
NE increases VG Ca and Na less negative RMP
