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Flashcards in The basis of excitability Deck (33):
1

What is the timescale for an action potential?

1-2msec

2

What causes depolarisation?

Na+ influx

3

What is depolarisation?

The cell becoming less negative

4

What does depolarisation do to PNa

It causes the opening of Na+ channels and PNa increases

5

What causes repolarisation?

K+ efflux

6

What is repolarisation?

The return of Em to resting potential

7

What does repolarisation do to Na+ gated channels?

Closes them

8

What is conductance of ions?

It is equivalent to permeability
Measured instead of permeability, membrane acts as an electrical resistor (R)
Conductance, g=1/R
Each ion has its own conductance

9

Conductance is proportional to what?

To the number of open ion channels

10

Change in gion will change what?

Em

11

Depolarisation opens which voltage-gated channels?

Na+ channels

12

What causes the initial depolarisation?

Synaptic activity
Generator potential (sensory neurone)

13

What does Em approach in the depolarisation phase?

ENa

14

What happens to Na+ channels in repolarisation?

They inactivate

15

When do K+ channels open?

As the neurone is repolarising, they open at positive values of Em

16

What is hyperpolarisation?

Em has returned to its initial value but K+ channels are still open
Em approaches Ek

17

How is hyperpolarisation dealt with?

The K+ channels finally close
The leak channels restore Em to resting value

18

What is the value of Ek?

-80mV

19

What is the value of ENa?

+62mV

20

What is the all-or-nothing principle?

An action potential either happens or it doesn't. They have no difference in size or power

21

What causes the all-or-nothing principle?

The existence of a threshold

22

What is the threshold?

The point at which an action potential will fire

23

What is happening in the neurone at the threshold value?

Na+ influx is greater than K+ efflux

24

What is the absolute refractory period?

No further action potential by any stimulus regardless of size

25

What is the relative refractory period?

A stronger stimulus will open sufficient Na+ channels and overcome increased gK that makes the threshold greater

26

Explain absolute refractory period in terms of voltage-gated channels?

Na+ are mostly inactivated
K+ are mostly open

27

Explain relative refractory period in terms of voltage-gated channels?

Na+ are recovering from inactivation
K+ some are still open

28

Why do action potentials not travel backwards in axons?

The membrane behind the action potential is in the refractory period

29

What is electrotonic spread?

The propagation of an action potential in an unmyelinated axon

30

How much faster is the speed of an impulse in a myelinated neurone?

1000x

31

What happens to the impulse in a myelinated neurone?

Jumps between nodes of Ranvier

32

What does the myelin sheath do?

Increases the speed of action potential conduction

33

What is saltatory conduction?

The jumping of the impulse between gaps in the myelin sheath