A-LevelBiologyControl and coordination9700/43 · Oct/Nov 2017 · Q59 Marks
Explain the importance of the myelin sheath in the transmission of action potentials.
- (a)Explain the importance of the myelin sheath in the transmission of action potentials.[4]
- (b)Acetylcholine is a neurotransmitter. Describe the events that occur at a synapse that lead to the release of acetylcholine.[5]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2017). The mark or mark type is shown in brackets.
- 5(a) four from:
- 1 insulator / ions cannot pass through it ;
- 2 depolarisation / action potentials, occur at nodes of Ranvier (only);
- 3 long(er) local, circuits / currents ;
- 4 action potential jumps from node to node / saltatory conduction ;
- 5 transmission / conduction, fast(er);
- 5(b) five from:
- 1 action potential / depolarisation, at presynaptic membrane ;
- 2 Ca²⁺ channels open / increased permeablity to Ca²⁺;
- 3 Ca²⁺ enter, (presynaptic) neurone / knob / axoplasm / AW ;
- 4 by (facilitated) diffusion / down concentration gradient;
- 5 vesicles, of acetylcholine / neurotransmitter, fuse with membrane ;
- 6 ACh / neurotransmitter, enters / exocytosed into, synaptic cleft ;
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