Q.Explain the process of the transport and release of a neurotransmitter with the help of a labelled diagram showing a complete neuron, axon terminal and synapse.

• A complete neuron has three main parts: dendrites that receive impulses, a cell body containing Nissl's granules, and a long axon ending in branched axon terminals, each tipped with a bulb-like synaptic knob.
• The synaptic knob is packed with synaptic vesicles containing neurotransmitter molecules, and it faces a narrow synaptic cleft that separates it from the next neuron's membrane.
• When an action potential reaches the synaptic knob, calcium ions enter and trigger the vesicles to move to and fuse with the presynaptic membrane, releasing neurotransmitter into the synaptic cleft. …

Since a labelled diagram cannot be drawn here, the structure and process can be laid out clearly in words, describing exactly what such a diagram would show.

Labelled parts of the neuron: begin with the dendrites, short branching fibres projecting from the cell body, which carry incoming impulses toward it. The cell body (cyton) contains the cytoplasm along with granular Nissl's granules. From the cell body extends the axon, a single long fibre that carries the impulse away; its distal end branches into several axon terminals, and each terminal ends in a bulb-like swelling, the synaptic knob. Inside each synaptic knob are numerous small sacs, the synaptic vesicles, filled with neurotransmitter molecules. Facing the synaptic knob, across a narrow gap labelled the synaptic cleft, lies the membrane of the next (postsynaptic) neuron, which carries specific receptor proteins.

The process of transport and release proceeds as follows:

• A nerve impulse (action potential) travels down the axon and arrives at the axon terminal/synaptic knob.
• Its arrival opens channels that let calcium ions enter the synaptic knob.
• This calcium entry causes the synaptic vesicles to move toward and fuse with the presynaptic membrane. …