Neuron Structure and Function

00:00 9 marks

**5.** The diagram shows the structure of a motor neuron.

[VISUALIZATION: Diagram of a typical vertebrate motor neuron. Label the following parts: Dendrites, Cell body (soma) with nucleus, Axon hillock, Axon, Myelin sheath (labelled A), Nodes of Ranvier, Axon terminal (synaptic terminal).]

(a) Identify the structure labelled A, which insulates the axon. [1]

(b) Outline how the resting potential is established and maintained in a neuron. [3]

Part a

1 minutes 1 marks

Question

(a) Identify the structure labelled A, which insulates the axon. [1]

Hint Hint

Hint

Look at the diagram provided and identify the segmented covering around the axon labelled A.

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Myelin sheath

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Part b

4 minutes 3 marks

Question

(b) Outline how the resting potential is established and maintained in a neuron. [3]

Hint Hint

Hint

Think about the ion pumps and ion channels in the neuron membrane and their relative permeabilities to different ions.

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Resting potential is established/maintained by the sodium-potassium pump (actively transports 3 Na+ out for 2 K+ in), greater membrane permeability to K+ than Na+ (due to K+ leak channels), leading to a net negative charge inside relative to the outside.

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Part c

8 minutes 5 marks

Question

Hint Hint

Hint

Detail the sequence of events starting from the action potential arriving at the axon terminal to the response in the postsynaptic neuron, including the role of acetylcholine.

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Action potential arrives at axon terminal, opening voltage-gated Ca2+ channels. Ca2+ influx triggers exocytosis of vesicles containing acetylcholine (ACh). ACh diffuses across synaptic cleft, binds to receptors on postsynaptic membrane, opening ligand-gated Na+ channels causing depolarization (EPSP). ACh is then broken down by acetylcholinesterase or reabsorbed.

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