Neuronal Excitability

Question 1

What is the threshold level?

Answer 1

Membrane potential at which depolarisations become an action potential

Question 2

What is the threshold level of most neurones?

Answer 2

-65mV

Question 3

Gradient of K+ ions in a nerve cell at rest

Answer 3

• Concentration gradient favours them diffusing out
• From 150mM (in) to 5.5mM (out)

Question 4

Gradient of Na+ ions in a nerve cell at rest

Answer 4

• Concentration gradient favours them diffusing in
• From 150mM (out) to 15mM (in)

Question 5

What is the Nernst Equation used to calculate?

Answer 5

Membrane potential at equilibrium for each ion in question

Question 6

Why is the resting potential closer to E(K) than E(Na)

Answer 6

Permeability to K+ is greater

Question 7

Basic generation of an action potential

Answer 7

1. Initial entry of Na+ causes depolarisation
2. If threshold reached, cell produces all-or-nothing potential
3. Steep depolarisation brings about further depolarisation of membrane

Question 8

What happens during the downstroke?

Answer 8

1. a) Depolarisation causes K+ channels to open
2. b) Depolarisation causes Na+ channels to close
3. a) K+ efflux
4. b) Na+ influx stopped
5. Repolarisation
6. Recovery after the action potential