Nerve impulses

Question 1

How is resting potential established

Answer 1

Sodium-potassium ion pump actively transports:
-3 NA+ ions out of axon
-2 K+ ions into the axon
This creates an electrochemical gradient (high k+ in than out and High Na+ out than in axon)
The membrane is more permeable to K+ than Na+ so more Na+ channels closed and More K+ channels open.
As a result K+ moves out of the axon by facilitated diffusion. inside of axon negatively charged so axon becomes polarised = resting potential

Question 2

Describe the all or nothing principle

Answer 2

1)Stimulus
-membrane more permeable to Na+ as Na+ channels open.
-Na+ diffuse into neurone down electrochemical gradient
2)Depolarisation
-P.d. reaches threshold, action potential generated because more voltage-gated Na+ channels open and Na+ diffuse rapidly.
3)Repolarisation
-Na+ channels close whilst K+ channels open so K+ diffuse out of the neurone.
4)Hyperpolarisation
-K+ channels slow to close so there’s a slight overshoot ( too many K+ diffuse out of neurone.
5)Resting potential restored
-by Na+ - K+ pump

Question 3

What is the refractory period

Answer 3

time to restore axon to resting potential so as a result no further action potential can be generated

Question 4

importance of refractory period

Answer 4

-Produces discrete and discontinuous impulses
-limits strength of impulses that can be detected; higher intensity stimulus causes higher frequency of action potentials but only up to certain intensity
-unidirectional action potential- can’t be propagated in a region that is refractory

Question 5

Factors which affect the speed of conductance

Answer 5

Myelination
Axon diameter
Temperature

Question 6

How does myelination affect the speed of conductance

Answer 6

Depolarisation at nodes of Ranvier which results in saltatory conduction
As a result there is no need to depolarise along whole length of axon unlike non-myelinated neurone

Question 7

How does axon diameter affect the speed of conductance

Answer 7

Bigger diameter means less leakage of ions

Question 8

How does temperature affect the speed of conductance

Answer 8

-Increases the rate of movement of Na+ and K+ as more kinetic energy for active transport/ diffusion
-Higher rate of respiration (enzyme activity faster) so ATP produced faster and energy released faster so active transport faster
-But proteins can denature at certain temp

Question 9

Passage along non-myelinated axon

Answer 9

action potenial passes as a wave of depolarisation

Question 10

Passage along myelinated axon

Answer 10

Depolarisation of axon at nodes of Ranvier
Results in Saltatory Conduction
So there is no need for depolarisation along whole length of axon