Topic 3 - NERVOUS SYSTEM I (Neuronal Physiology - Refractory Period & All or None Principle of AP)

Question 1

refractory period of an ap

• what are the 2 refractory periods called?

Answer 1

1. absolute refractory period (prevents AP summation)
2. relative refractory period

Question 2

Absolute refractory period (prevents AP summation)

• NO…
• results from what?

Answer 2

• NO AP can be generated, regardless of stimulus size
• results from either:
  
  • all voltage-gated Na+ channels are open OR
  • Na+ channels are inactivated (cannot open until MP passes RMP)

Question 3

Relative Refractory Period

1

1. 2. Na+ channels are reactivated when MP passes RMP therefore, they are closed but can be reopened if threshold reached
2. K+ channels are open and membrane is hyperpolarized
3. further to got to get to threshold therefore need larger stimulus

Answer 3

period when an AP can be generated but only by a greater than normal stimulus

Question 4

relative refractory period

2

1. period when an AP can be generated but only by a greater than normal stimulus
2. 3. K+ channels are open and membrane is hyperpolarized
3. further to got to get to threshold therefore need larger stimulus

Answer 4

Na+ channels are reactivated when MP passes RMP therefore, they are closed but can be reopened if threshold reached

Question 5

relative refractory period

3

1. period when an AP can be generated but only by a greater than normal stimulus
2. Na+ channels are reactivated when MP passes RMP therefore, they are closed but can be reopened if threshold reached
3. what happens to K+ channels
4. further to got to get to threshold therefore need larger stimulus

Answer 5

K+ channels are open and membrane is hyperpolarized

Question 6

relative refractory period

4

1. period when an AP can be generated but only by a greater than normal stimulus
2. Na+ channels are reactivated when MP passes RMP therefore, they are closed but can be reopened if threshold reached
3. K+ channels are open and membrane is hyperpolarized
4. what do you need to go to get to threshold?

Answer 6

further to go to get to threshold therefore need larger stimulus

Question 7

All or None Principle of APs

ALL

Answer 7

if threshold reached, AP is produced - same everytime (same max depolarization etc)

Question 8

All or None Principle of APs

NONE

Answer 8

below threshold ⇒ no AP