The Nervous System

Question 1

Structure of a neuron

Answer 1

1. Dendrite
2. Cell body
3. Nucleus
4. Axon hillock
5. Axon
6. Myelin sheath
7. Nodes of Ranvier
8. Axon terminal

Question 2

How do impulses travel along a myelinated axon?

Answer 2

Saltatory conduction (impulse jumps from node to node)

Question 3

Name the different phases that occur when an impulse passes along an axon.

Answer 3

1. Depolarisation (+30/40 mV)
2. Repolarisation (returns to -70 mV)
3. Hyperpolarisation (overshoots resting potential)
4. Returns to resting potential

Question 4

Describe the process of depolarisation

Answer 4

1. Na+ channels open
2. This causes an influx of Na+
3. Membrane becomes more positive and action potential is produced if 30 mV is reached

Question 5

Describe the process of repolarisation

Answer 5

1. Na+ channels close
2. K+ voltage-gated channels open
3. Membrane more permeable to K+

Question 6

Describe the process of hyperpolerisation

Answer 6

1. Membrane potential overshoots -70 mV

2. This is because K+ channels close slowly

Question 7

Describe the process of the membrane returning to resting potential

Answer 7

1. Na+/K+ pump brings in 2 K+ and pumps out 3 Na+ so membrane becomes -70 mV again