<P> Neurons are interconnected in complex arrangements, and use electrochemical signals and neurotransmitter chemicals to transmit impulses from one neuron to the next; axon terminals are separated from neighboring neurons by a small gap called a synapse, across which impulses are sent . The axon terminal, and the neuron from which it comes, is sometimes referred to as the "presynaptic" neuron . </P> <P> Neurotransmitters are packaged into synaptic vesicles that cluster beneath the axon terminal membrane on the presynaptic side of a synapse . The axonal terminals are specialized to release the neurotransmitters of the presynaptic cell . The terminals release transmitter substances into a gap called the synaptic cleft between the terminals and the dendrites of the next neuron . The information is received by the dendrite receptors of the postsynaptic cell that are connected to it . Neurons don't touch each other, but communicate across the synapse . </P> <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>

What type of ion channels is necessary for the function of the axon and the axon terminal