Dr. Tran Physiology

Question 1

What would a low ERP/APD ratio signify?

Answer 1

This would suggest tissue that could easily propagate abnormal impulses.

Question 2

During the resting state, which gates are closed in the Cardiac Na channel?

Answer 2

The activation gate is closed with the inactivation gate open.

Question 3

At which phase do the sodium channels begin coming out of the inactivated state in myocardial tissue?

Answer 3

During phase III as the membrane becomes negative enough for them to return to the rested state from the inactivated state.

This is essentially the ERP and the RRP.

Question 4

What pathology follows abnormally long late sodium channel conducting time?

Answer 4

Excessive intracellular sodium leads to excessive Calcium (Na/Ca exchanger stops)

Leads to Ca2+ overload causing mechanical dysfunctions and after depolarization problems.

Question 5

Which phase of the action potential is prolonged by potassium channel activity?

Answer 5

Phase III is prolonged.

Question 6

What effect will be observed in the pacemaker cells if Ca2+ channels are blocked?

Answer 6

Phase 4 and phase O slopes will be reduced.

This ultimately reduces heart rate.

Question 7

What phase does calcium effect in myocardial cells?

Answer 7

Effects phase 3 plateau.

Question 8

What effect do calcium channel blockers have on the myocardium?

Answer 8

Little to no effect on the myocardium. Mostly effects the supraventricular nodes.

Question 9

What is the difference that is observed in sympathetic activity within myocardial cells vs nodal cells/

Answer 9

In the nodal cells sympathetic activity increases phase 4 slop causing a faster heart rate.

In the myocardium sympathetic activity increases ionortropy, lusitropy (relaxation) and increases O2 demand.