Neuronal excitability

Question 1

Action potential

Answer 1

When at rest, if a neurone is activated, its membrane potential will depolarise from RMP. If the membrane is depolarised beyond threshold level, it will suddenly generate and all-or-nothing event called an action potential.

Question 2

Resting membrane potential

Answer 2

The membrane potential maintains a value of -70mV until the cell is either activated or inhibited.

• inside, there is a large concentration of K+
• outside, there is a large concentration of Na+

Question 3

Nernst equation

Answer 3

Can be used to calculate the membrane potential at equilibrium for each of the ions in question.

Question 4

Ionic basis of RMP

Answer 4

At RMP, there is a slow leak of Na+ ions into the cell and K+ ions out of the cell. The Na+/K+ ATPase maintains the ionic concentration gradient over time. The amount of Na+ entering is the same as K+ leaving, but as permeability to K+ is greater the RMP is closer to Ek.

Question 5

Ionic basis of NAP

Answer 5

1) initial entry of Na+ ions leads to depolarisation from RMP
2) if the cell is depolarised to its threshold level, an action potential will be generated
3) steep depolarisation leads to further depolarisation in a positive feedback mechanism–> Na+ channels open
4) repolarisation as K+ channels open and Na+ channels are inactivated
5) hyperpolarisation during the recovery period after an AP