Action Potentials

Question 1

What are the steps of an action potential?

Answer 1

1. Leaky K+ channels allow K+ to leave cells.
2. Na+ VGCs open, Na+ enters cells. DEP.
3. Na+ VGCs close, K+ VGCs open. K+ leaves the cell. REP.
4. K+ VGCs close slowly. Resting membrane potential is reached. HYP.

Question 2

Give properties of action potentials.

Answer 2

Has a threshold.
Has a refractory period.
All-or-nothing.
Self-propagating.
Travels slowly.
Intensity is proportional to frequency.
Mediated by VGCs.

Question 3

How does the size of axons make self-propagations faster?

Answer 3

Less electrical resistance.
Na+ channels are more spaced out.
Less energy maintaining ion gradients.

Question 4

How does myelination make self-propagations faster?

Answer 4

Increases membrane resistance.
Decreases membrane capacitance.
Causes saltatory conduction.

Question 5

What are the consequences of demyelination?

Answer 5

Decreases membrane resistance.
Increases membrane capacitance.
Conduction fails.
MS - CNS.
Guillain-Barré Syndrome - PNS.

Question 6

Describe extracellular recordings.

Answer 6

Uses electrodes outside axons.
Relative to earth.
A bundle of axons are electrically stimulated and all the small action potentials add up to make large waves.

Question 7

How are action potentials recorded?

Answer 7

Intracellular.
Uses microelectrodes through the membrane.
Relative to the outside of the cell.