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Flashcards in Cardiac Conduction Deck (26)
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1

What is the intercalated disk?

The intercalated disk is a region of intracellular connections between cardiac cells. Gap junctions allow the propagation of APs between cardiac cells through connexons which determine the internal resistance.

2

What is the function of the SA node?

Pacemaker - slow conduction

3

What is the function of the AV node?

Pacemaker - slow conduction

4

What is the function of atrial and ventricular muscle?

Contraction - rapid conduction

5

What is the function of the His-Purkinje Bundle?

Very rapid conduction to coordinate the simultaneous contraction of the left and right ventricles

6

How is the space constant related to the electrical conduction between cardiac cells?

The space constant is related to the membrane and internal resistances which is also related to the K+ permeability, the gap junction connexons and cell diameter.

7

How does the upstroke of the action potential related to the rate of conduction of the cell?

Upstroke of the action potential is related to the Na channels available which is related to the rate of conduction.

8

How is the resting membrane potential related to the availability of Na channels?

The higher the RMP is, and thus, the more depolarized it is, the less Na channels that will be available and the slower conduction will be.

9

What is the P-R interval?

It is the conduction time from the atria to the ventricles

10

What is the QRS complex?

It is the conduction through the ventricle sand it should be <100 ms

11

What NT does the parasympathetic nervous system use to regulate the cardiac conduction?

Acetylcholine

12

What NT does the sympathetic nervous system use to regulate the cardiac conduction?

Norepinephrine

13

How does ACh affect the conduction of the AV node?

ACh increases K+ membrane permeability which leads to hyper polarization of the RMP, making it harder for it to reach thresholds and activate action potentials -> inhibition of the SA/AV nodes

14

How does NE affect the conduction of the AV node?

NE binds β-adrenergic receptors, which increase cAMP leading to an increase in the slow Ca current -> affects all areas of the heart: increasing atrial and ventricular contraction and increases the SA node rate and AV node conduction and the P-R interval is decreased as a result.

15

How will an ACh affected cardiac cycle show up on the EKG?

The P-R interval will be lengthened

16

How will an NE affected cardiac cycle show up on the EKG?

The P-R interval will be shortened

17

What is 1st degree AV block?

Abnormal elongation of the P-R interval.

18

What is 2nd degree AV block?

Not all P-waves are followed by a QRS, indicating that the atria are failing to activate the ventricles.

19

What is 3rd degree AV block?

Complete AV node block so that there is no consistent P-R interval. The ventricles and the atria are completely disconnected.

20

What is supra ventricular tachycardia?

It is a rapid rhythm originating at or above the AV node and the conduction through the ventricles is normal with normal QRS duration. The HR is fast but ventricles are normal and so stroke volume is normal.

21

What is ventricular tachycardia?

It is a rapid rhythm that originates in the ventricles because conduction is slow and it does not travel through the His-Purkinje system. The QRS duration is prolonged and ventricle motion is abnormal, compromising stroke volume.

22

What is atrial fibrillation?

Due to reentry of excitation and the disorganized electrical activity causes asynchronous contraction which ceases pumping. Not life threatening due to most of the atrial blood not requiring contraction to pump into the ventricles.

23

What is ventricular fibrillation?

Due to reentry of excitation and the disorganized electrical activity causes asynchronous contraction which ceases pumping. This is rapidly fatal as the ventricular contraction is crucial in order to perfuse the body and the heart itself.

24

What is the injury current?

It is a current that occurs in the heart as a result of infarcted tissue. The gap junctions running through the cells are damaged and causes the abnormality.

25

What is healing over?

An injury current can disappear from detection if the gap junctions connecting infarcted tissue are shut down. The current will disappear but that does not mean that the infarcted tissue has healed.

26

What can influence the upstroke of the action potential?

Hyperkalemia
Premature Excitation during the Relative Refractory Period
Ischemia or Infarction

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