Basic Principles of Neurotransmission
When the nerve impulse arrives at the terminal, it triggers a calcium - dependent fusion of neurotransmitter packets or vesicles with the nerve terminal plasma membrane, followed by release of the neurotransmitter into the gap, or synapse, between the nerve cells. The neurotransmitters and neuromodulators bind to specific plasma membrane receptors, which transmit the information that the neurotransmitter has brought to the receiving cell by means of other membrane proteins and intracellular ‘second messengers’.
The neurotransmitters are inactivated by enzymes or taken up into the nerve that released them and metabolized. The release of the neurotransmitter may be modulated and limited by: (i) autoreceptors on the nerve terminal from which it was released, so that further release of the neurotransmitter is inhibited; and (ii) by presynaptic inhibition, when another neurone synapses with the nerve terminal.