Cardiac Action Potential Flashcards Preview

Physiology III > Cardiac Action Potential > Flashcards

Flashcards in Cardiac Action Potential Deck (14)
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1
Q

Why does the heart have two different action potentials?

A

The myocytes have a separate AP than the pacemaker cells of the heart

2
Q

Why is there a plateau in the cardiac AP of myocytes?

A

Voltage gates Ca channels open, small Na influx via same Ca channels and K conductance is decreased

3
Q

When does systole and diastole occur on the cardiac AP?

A

Systole is seen during AP generation (upstroke) and diastole is seen at resting membrane potential

4
Q

What part of the pacemaker cells action potential can be changed in order to increase heart rate?

A

Phase four can be sped up by an increase in conductance to Na ion (this is where drugs work)

5
Q

What does the notch on the myocyte AP represent?

A

Na gate closes, K efflux but Ca channels open which causes the cell from completely repolarizing

6
Q

What conducts the AP from the atria to the ventricle?

A

A-V bundle (delayed from decrease in gap junctions)

7
Q

What carries the AP from the right atria to the left atria?

A

Internodal fibers course through the atria from right to left

8
Q

Why is there a delay at the A-V node?

A

In order to prevent the atria and ventricles from pumping at the same time

9
Q

What two factors prevent an AP from traveling from ventricle to atria?

A

A-V bundle is specialized one way conduction

Atria are electrically insulated from the ventricle by fibrous tissue

10
Q

Why is it beneficial to depolarize from epi to endocardium and depolarize from endo to epicardium?

A

Prevents tetany of the cardiac muscle

11
Q

Since the sarcoplasmic reticulum is less developed in cardiac myocytes, how do these cells obtain Ca for contraction?

A

Enhanced t-tubule system, bring more ECF to cardiac myofibrils, this means more Ca

12
Q

In a healthy heart, why doesn’t tetany occur?

A

The mechanical event ends prior to the end of the electrical event

13
Q

How does the parasympathetic nervous system impact the rate of the heart?

A

Ach is released by the vagus nerve, Ach increases VG K channel which hyperpolarizes RMP (decreased HR)

14
Q

What four factors are enhanced by SNS activation of the myocytes?

A

Increase SA node rhythm
Increased excitability of AV fibers (faster transmission)
Increased force
NE increases VG Ca and Na less negative RMP