Prior to neurotransmitter release, vesicles are transported to specialized regions of the presynaptic terminal called _ zones, where they bind to the terminal in a process known as _.

An impulse after travelling along the dendrites, cell body and axon of a neuron reaches the axon endings in the form of an action potential (signal transmitted by the activation of voltage gated sodium and potassium channels present on the plasma membrane of the neurons).
At the axon ending or the pre-synaptic region, the action potential triggers the opening of the voltage dependent calcium channels, that promotes the influx of calcium ions into the pre-synaptic region of the neuron.
This process triggers the fusion of the neuro-transmitter carrying vesicles with the plasma membrane in the pre-synaptic region of the neuron.
As a result of fusion the neurotransmitter is released into the synaptic cleft.
At the pre-synaptic region of the neuron, there is a huge concentration of neuro-transmitter carrying vesicles which remain adhered to proteins called CAZ (cytomatrix at the active zone) proteins. These proteins help the neurotransmitter carrying vesicles to remain tethered or docked to the pre-synaptic membrane in the axon terminal of the neuron. They together form the Synaptic Active Zone.

In response to calcium ion influx these proteins help the neurotransmitter carrying vesicles to fuse with the plasma membrane in the pre-synaptic region of the neural axon and release the neurotransmitter into the synaptic cleft.
The process of fusion of the neurotransmitter carrying vesicles with the plasma membrane in the pre-synaptic region of the neural axon followed by the release of the neurotransmitter into the synaptic cleft is known as Exocytosis.

Prior to neurotransmitter release, vesicles are transported to specialized regions of the presynaptic terminal called _______ zones, where they bind to the terminal in a process known as _______.