Describe the structure of a motor neurone.

Mark scheme

Marking points from the official mark scheme (May/June 2017). The mark or mark type is shown in brackets.

1. max 6 of:
2. 1 dendrites (lead to cell body); R at both ends
3. 2 nucleus in, cell body / soma; R if cell body not at one end
4. 3 many mitochondria (in cell body);
5. 4 much RER / Nissl's granules (in cell body);
6. 5 long/one, axon; A an axon
7. 6 synaptic, knobs / termini / boutons, at end furthest from cell body;
8. 7 Schwann cells / myelin ;
9. 8 nodes of Ranvier ;
10. accept points on labelled diagram
11. max 9 of:
12. 1 Na⁺ / sodium ion, channels open ; I ligand or voltage gated
13. 2 Na⁺ enters, cell / axon ; A Na ions / sodium ions
14. 3 inside / p.d., becomes, less negative / positive / +40 mV or causes depolarisation (in correct context);
15. 4 Na⁺ / sodium ion, channels close ; ecf from mp1 I ligand or voltage-gated
16. 5 K⁺ / potassium ion, channels open ; ecf from mp1 I ligand or voltage-gated
17. 6 K⁺ moves out (of cell) ; A K ions / potassium ions
18. 7 inside / p.d., becomes negative / A negative figure or causes repolarisation (in correct context);
19. 8 local circuits ;
20. 9 myelin (sheath) / Schwann cells, insulate / prevent ion movement ;
21. 10 action potential / depolarisation, only at, nodes (of Ranvier);
22. 11 saltatory conduction / action potential jumps from node to node; A impulse for AP
23. 12 one-way / unidirectional, transmission ;
24. 13 AVP; e.g. hyperpolarisation / refractory period