13.4 Nervous transmissions

Question 1

Resting potential

Answer 1

When neurone is not transmitting an impulse
Potential difference between the inside and the outside of the axon
Charge is more positive outside the axon than the inside
-70 mV

Question 2

How is resting potential created?

Answer 2

1) Na+ ions transported out of the axon (3)
K+ ions actively transported into the axon by Na+/K+ pump (2)

2) More Na+ out than inside, more K+ inside than outside, so Na+ diffuse back in and K+ out down the electrochemical gradient

3) Most of Na+ channels are closed - prevent movement of Na+, but most K+ channels are open, and K+ diffuse out

4) There are more positive ions outside than inside, creating the resting potential of -70 mV

Question 3

Depolarisation

Answer 3

Stimulus is detected, energy of stimulus temporarily reverses charges on the axon membrane, so potential difference changes and becomes +40 mV

Question 4

Repolarisation

Answer 4

When impulse passes, potential difference from positive to negative and returns to its resting potential

Question 5

What happens during action potential?

Answer 5

1) Neurone is at resting potential
Some K+ channels are open
Na+ voltage gated channels are closed

2) Energy of stimulus causes VG Na+ channels to open, so Na+ diffuses into axon and inside of neurone becomes less negative

3) Change in charge causes more Na+ channels to open, as an example of positive feedback

4) Pd reaches +40 mV, Na+ channels close, VG K+ channels open. Na+ cannot enter but K+ can diffuse out

5) K+ diffuse out down the electrochemical gradient, inside of axon becomes more negative than the outside

6) Lots of K+ diffuse out, inside becomes more negative than the resting state - hyperpolarisation
VG K+ channels close, Na+/K+ pump causes Na+ to go out and K+ in
Axon returns to resting potential - repolarisation