<P> The neurotransmitter molecule packages (vesicles) are created within the neuron, then travel down the axon to the distal axon terminal where they sit docked . Calcium ions then trigger a biochemical cascade which results in vesicles fusing with the presynaptic membrane and releasing their contents to the synaptic cleft within 180 μs of calcium entry . Triggered by the binding of the calcium ions, the synaptic vesicle proteins begin to move apart, resulting in the creation of a fusion pore . The presence of the pore allows for the release of neurotransmitter into the synaptic cleft . The process occurring at the axon terminal is exocytosis, which a cell uses to exude secretory vesicles out of the cell membrane . These membrane - bound vesicles contain soluble proteins to be secreted to the extracellular environment, as well as membrane proteins and lipids that are sent to become components of the cell membrane . Exocytosis in neuronal chemical synapses is Ca triggered and serves interneuronal signalling . </P> <Table> Structure of a typical neuron <Tr> <Th> Neuron </Th> </Tr> <Tr> <Td> Dendrite Soma Axon Nucleus Node of Ranvier Axon terminal Schwann cell Myelin sheath </Td> </Tr> </Table> <Tr> <Th> Neuron </Th> </Tr> <Tr> <Td> Dendrite Soma Axon Nucleus Node of Ranvier Axon terminal Schwann cell Myelin sheath </Td> </Tr>

Exocytosis of neurotransmitters from the axon terminal requires