Neurons 2

Question 1

What is an action potential?

How is an AP caused?

Answer 1

• AP is a brief fluctuation in MP (spike/nerve impulse/discharge)
• Caused by transient opening of voltage-gated ion channels / which spreads along parts of neuron

Question 2

What are the 3 stages of the AP? (what happens before this?)

Answer 2

(Depolarisation to threshold (-55mV))

1. Fast depolarisation (~+30mV)
2. Repolarisation
3. After-hyperpolarisation (more neg)

Question 3

What is the absolute refractory period (ARP)?

Answer 3

Another AP CANNOT be triggered (usually during depolarisation)

Question 4

What is the relative refractory period (RRP)?

Answer 4

Another AP MAY be triggered (usually during repolarisation)

Question 5

What happens in stage 1: fast depolarisation?

Answer 5

Voltage-gated Na channels open fast
(Na»>K)
(Absolute refractory period)

Question 6

What happens in stage 2: repolarisation?

Answer 6

• Voltage-gated Na channels close
• Voltage-gated K channels open
  (K»>Na)
  (Relative refractory period)

Question 7

What happens in stage 3: after-hyperpolarisation?

Answer 7

• Voltage-gated K channels stay open for a while, then they close
  (K»>Na then K»Na)

Question 8

What direction does current flow?

Answer 8

Anode (+) to cathode (-)

Question 9

How does myelination of the axon increase AP conduction velocity?

Answer 9

Increases the efficiency of passive spread

Question 10

What is saltatory conduction?

Answer 10

APs are generated only at nodes of ranvier, and current flows passively between nodes

Question 11

State the steps in generation of AP in sensory neurons (4)

Answer 11

1. Stimulus acts on receptors in SENSORY neuron
2. Evokes graded DEpolarisation in sensory endings = receptor potential
3. Receptor potential spreads PASSIVELY to trigger zone (where APs are generated)
4. APs spread along axon towards CNS