neurotransmitter

The arrival of a nerve impulse stimulates the release of neurotransmitters from vesicles. They pass across the synapse and open channels in the target cell. Charged particles can then enter and trigger a second impulse.

A chemical that mediates the transmission of a nerve impulse across the synapse between neurons and target cells. Neurotransmitters either stimulate or inhibit electrical impulses in target cells.

More than 50 neurotransmitters have been identified. Important examples include adrenaline and noradrenaline (in adrenergic nerves) and acetylcholine (in cholinergic nerves).

The neurotransmitter is released at the synaptic knob at the tip of an axon into the synaptic cleft. It diffuses across to the opposite membrane (the postsynaptic membrane), where it triggers the propagation of a nerve impulse in the next neuron.

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• ANATOMY AND PHYSIOLOGY

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