Action Potentials

Question 1

What is the axon hillock responsible for?

Answer 1

The propagation of action potentials

Question 2

How is an action potential generated?

Answer 2

Accumulation of graded potentials

Question 3

When do voltage gated K+ channels open and close?

Answer 3

+30mV
Shortly after RMP is re-established

Question 4

How does RMP get restored?

Answer 4

K+ “leak” channels allow minor readjustments to RMP

Question 5

How long does the refractory period of Na+ channels last?

Answer 5

2-3 ms

Question 6

What is the role of myelin?

Answer 6

Myelin sheaths cause HCN channels to aggregate in unmyelinated regions along the axon allowing efficient propagation of action potentials

Question 7

What is multiple sclerosis?

Answer 7

Myelin is degenerating or entirely absent, resulting in inefficient transmission of APs

Question 8

What is the relationship between the amount of neurotransmitter released, magnitude of the graded potential and number of action potentials?

Answer 8

They’re directly proportional to each other

Question 9

How do local anaesthetics work?

Answer 9

Reversibly bind to voltage gated Na+ channels, reducing the ability of membrane potential depolarisations to produce action potentials

Question 10

What is primary hyperkalaemic paralysis?

Answer 10

Painful spontaneous muscle contractions followed by periods of paralysis
Plasma and ECF have elevated K+
Mutations in Na+ channels reduce the rate of voltage inactivation and longer lasting APs increasing K+ secretion
Elevated ECF K+ depolarises increasing likelihood of APs
Na+ channels become refractory

Question 11

What happens if demyelination is very severe in multiple sclerosis?

Answer 11

AP may arrive at next node of Ranvier with insufficient strength to fire an AP