Action Potential

Question 1

How do you record resting and action potentials?

Answer 1

Insert an electrode into the cell and one outside the cell. The oscilloscope shows resting potential

Question 2

What does it mean if you measure outward current?

Answer 2

It means that positive current is going out of the cell.

Question 3

Describe the shape of an action potential.

Answer 3

1. Resting (-70mV)
2. Depolarization
3. Repolarization
4. Hyperpolarization
5. Resting state

Question 4

What is absolute refractory period?

Answer 4

A period where Na gates are inactive; during this period no stimulus will trigger an action potential; limits max firing rate to 1000 Hz

Question 5

What is relative refractory period?

Answer 5

Period where membrane is trying to go back to resting; only strong stimulus may trigger an action potential

Question 6

When is action potential triggered?

Answer 6

When membrane depolarizes about 10-20 mV

Question 7

What technique did Hodgkin, Huxley, and Katz use?

Answer 7

Voltage clamp technique

Question 8

What is voltage clamp technique?

Answer 8

Allows one to control the membrane potential at any level while measuring the current necessary to maintain that membrane potential

Question 9

What follows a brief capacitive current? After that?

Answer 9

rapidly rising inward ionic current (Na), followed by a slower delayed outward current(K).

Question 10

How can we eliminate the early inward current that follows a brief capacitive current?

Answer 10

Replace sodium with choline.

Question 11

What poisons block voltage-gated Na channels?

Answer 11

TTX, STX, and conotoxins

Question 12

What poisons blocks voltage-gated K channels?

Answer 12

TEA and 4-aminopyridine

Question 13

Evidence for Na current

Answer 13

1. Equilibrium potential = +55 mV
2. Ionic substitution
3. Use of TTX

Question 14

Evidence for K current

Answer 14

1. Ionic substitution
2. Use of TEA

Question 15

Describe action of proteins during action potential?

Answer 15

1. During rest, only leak K channels open.
2. During depolarization, voltage-gated Na channels open
3. At overshoot, voltage-gated Na channels close and voltage-gated K channels open
4. During repolarization, Na channels close
5. During resting, voltage-gated K channels close

Question 16

After determining ion currents during action potentials, what did Hodgkin and Huxley calculate?

Answer 16

Magnitude and time course of the conductance change for each ion

Question 17

What are three important phenomena in the voltage-dependent conductance model?

Answer 17

1. Both conductance’s are voltage-dependent
2. Both conductance’s change over time
3. Activation saturates

Question 18

What happens to the conductance of Na and K when neuron depolarizes?

Answer 18

The conductance increases

Question 19

Why does the rate of depolarization decrease?

Answer 19

1. the driving force for sodium decreases
2. sodium channels become inactivated
3. potassium channels open

Question 20

Describe positive feedback loop of ionic currents during action potential

Answer 20

Depolarization causes increase in sodium conductance which causes inward sodium current which causes more depolarization

Question 21

Describe negative feedback loop of ionic currents during action potential

Answer 21

Depolarization causes an increase in potassium conductance which causes outward potassium current which causes repolarization.

Question 22

Two functions of refractory period

Answer 22

1. Limits the firing frequency
2. causes the AP to continue propagating in one direction

Question 23

How is AP regenerated?

Answer 23

Opening new adjacent sodium channels

Question 24

What is concentrated at nodes and paranodes of myelinated axons?

Answer 24

Voltage-gated K and Na channels

Question 25

Generally why do dendrites and neuronal cell bodies not generate APs?

Answer 25

low density of voltage-gated sodium channels

Question 26

What has the highest density of voltage-gated sodium channels?

Answer 26

axon hillock

Question 27

Local anesthetics?

Answer 27

Lidocaine acts as reversible inhibitors of voltage-gated sodium channels