The Action Potential: Long Distance Communication

Question 1

Action potentials

Answer 1

Action potentials require special, voltage gated ion channels

Question 2

AP conduction

Answer 2

rely on summation for transmission and signal gets smaller along the axon

Question 3

initial segment

Answer 3

All neurons have an “initial segment” and is the site of initiation of action potential

Question 4

what triggers an AP

Answer 4

An AP can be triggered by a depolarising local potential reaching the initial segment - if it is large enough

Question 5

AP commitment

Answer 5

action potential is all or none

= all sodium channels are open/activated

Question 6

IF ASKED TO DESCRIBE LINE OF AP

Answer 6

rising phase is caused by a sodium influx, at this phase all sodium channels are open and then at the peak, become inactivated. The permeability to sodium then starts to drop until all all sodium channel are open or inactived (non left to activate). The permeability of potassium increases which causes the falling phase of the action potential and caused by potassium efflux coming out of the cell. It regenerates itself as it goes from Na channels to Na channels along the whole axis

Question 7

The AP refractory period(s)

Answer 7

can’t produce another AP during the absolute refractory period therefore frequency is limited by the aboslute refractory period ARP

Question 8

Relative refractory period

Answer 8

can set off another AP but need another higher voltage to fight against K current (has to overcome flood of potassium coming out)
AP will be same size as it is all or none, once set up it will go to +30 (won’t be smaller)

Question 9

Absolute refractory period (ARP):

Answer 9

Impossible to trigger an AP

•Na+ channel inactivation

Question 10

Relative refractory period (RRP):

Answer 10

• Larger than normal stimulus required

* Some residual Na channel inactivation • High K+ permeability

Question 11

Action potential propagation - unmyelinated axons I

Answer 11

AP at one point triggers AP in the next section
adjacent inactive area into which depolarising is spreading, will soon reach threshold
remainder of axon still at resting potential

Question 12

Action potential propagation - unmyelinated axons II

Answer 12

Due to the refractory period, APs cannot “change directions”

refractory zone > AP zone > proceding depol

Question 13

Action potential propagation - myelinated axons 2

Answer 13

APs occur only at Nodes of Ranvier: saltatory conduction
active node at peak of action potenital > adjacent inactive area into which depolarising is spreading, will soon reach threshold > remainder of nodes still at resting potential

• current goes forward to activate next node and backwards to equilibrate

Question 14

Action potential propagation - myelinated axons III

Answer 14

Due to the refractory period, APs cannot “change directions”
previous active node returned to resting potential ? adjacent node that was brought to threshold local current flow, now active at peak of potential > new adjacent inactive area into which depolarising is spreading, will soon reach threshold