Membrane Excitability- Lecture 18

Question 1

What is passive membrane behavior?

Answer 1

when a current flows across a membrane that contains only voltage-independent “leak” channels and Vm returns directly to its original value when the current ends

Question 2

What is active membrane behavior?

Answer 2

when the dynamics of currents flowing through voltage-dependent channels as their conductances respond to changes in Vm

Question 3

What is an action potential?

Answer 3

an all or none stereotyped sequence of changes in Vm

Question 4

What is the absolute refractory period?

Answer 4

the time that is required for recently inactivated channels to de-inactivate and become available for generating a new action potential

Question 5

What is the relative refractory period?

Answer 5

when, at somewhat longer intervals, small amplitude, shallow-slope spikes can be initiated as more Na+ channels de-inactivate

Question 6

What are the five phases of the action potentials in the ventricle?

Answer 6

Phase 0: activation fo voltage-gated Na+ channels, Kir channel conductance declines
Phase 1: inactivation of most Na+ channels
Phase 2: Activation of voltage gated Ca2+ channels
Phase 3: inactivation of Ca2+ channels; activation of voltage-gated K+ channels (followed by their inactivation in Phase 4)
Phase 4: dominated by Kir channels