(a) Serotonin is a neurotransmitter which is produced by certain neurones in the brain. One of its effects is to increase the activity of sensory neurones in the brain. It also usually improves a persons mood and keeps them awake. the diagram shows a synapse at which serotonin is the neurotransmitter.

(i) Explain how the release of the neurotransmitter serotonin, by neurone A would initiate an impulse in neurone B.




The serotonin is normally rapidly reabsorbed from the synaptic cleft by 5HT carrier proteins in the presynaptic membrane. Suggest one advantage of rapidly reabsorbing the serotonin.



NEAB 1999

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