Identify I,II,III in the following image

Axon I II Ion channel Dendrite

The correct option is A I - Vesicle with neurotransmitters, II - Synaptic cleft, III- Postsynaptic receptor area.
1. At the junction of the synapse. The neuron prior to the synapse is termed presynaptic neuron and the one subsequent to it is called the postsynaptic neuron.
2. When an action potential in a presynaptic neuron has been propagated to the axon terminal a local change in potential triggers the opening of voltage-gated calcium channels in the synaptic knob. 3. The Ca2+ is much more highly concentrated in the ECF and its electrical gradient is inward, this ion flows into the synaptic knob through the opened channels and induces the release of a neurotransmitter from some of the synaptic vesicles into the synaptic cleft
4. The neurotransmitter released by exocytosis diffuses across the cleft and binds with specific protein receptor sites on the postsynaptic membrane.
5. The final step is when, this binding triggers the opening of specific ion channels in the postsynaptic membrane, changing the ion permeability of the postsynaptic neuron. This triggers a change in the membrane potential of the dendrites and leads to the generation of an action potential.
6. Neurotransmitters don't stay bonded to their receptors for more than a few milliseconds. After they deliver their message they either degrade or get recycled. Some of these diffuse back across the synapse and can get reabsorbed so that they can be reused. This process is called “reuptake”.