Lecture14

Question 1

Describe ionic basis of an action potential.

Answer 1

Na depolarize - Na comes inside cell and makes cell interior positive

K hyperpolarization- k leaves the cell making the cell more negative

Question 2

Define the following properties of ion channels:

gating, activation, and inactivation.

Answer 2

Gating: relationship between vm and gate opening or closing; gates are independent

Activation
Allow flow of that particular ion; gate is open

Inactivation
Gates are closed; no flow of that particular ion

Question 3

Know the properties of voltage-gated Na+, K+, and Ca2+ channels, and understand that voltage influences their gating, activation, and inactivation.

Answer 3

Voltage gates
H: inactivation gate
M: activation gate

Na voltage gate
Resting state: activation gate closed +
Inactivation gate open

Depolarization: activation gate open +. Inactivation gate open = full Na flux

Repolarization: activation gate open but inactivation gate closed = absolute refractory period

Resetting to resting state: activation gate close but inactivation gate open

Long slow depolarization

• Lock Na inactivation gates
• increase delayed k channel conductance

Question 4

Understand how the activity of voltage-gated Na+, K+, and Ca2+ channels generates an action potential and the roles of those channels in each phase (depolarization, overshoot, repolarization, hyper polarization) of the action potential.

Answer 4

Depolarization
Na channels open
Vm is never at the ENa because the Na channels are never the only ones opened

At 30 mV = both Na and k channels are open

Hyperpolarization
Na channel start to close
K channel open
Vm approached Ek

Overshoot
K channel open
Na are in inactive state and cannot be reactivated
Refractory period

Resting membrane potential
Na channels are off but can be deactivated and k channels open
Vm stabilizes around Ek