What is synapse?

The synapse is the structure that mediates the effects of a nerve impulse on a target cell, permitting communication among nerve cells, muscles and glands.  It is contact point where information is transferred. Usually, synapses are made between the axon of a presynaptic neuron, the sender and the dendrite of a postsynaptic neuron, the receiver.

There are two types of synapses electrical synapses and chemical synapses. Chemical synapses may act either directly through ion channels or indirectly through second messengers.

A single neuron can have up to approximately 10,000 synapses. Changes in the number and strength of synapses, called synaptic plasticity are thought to be biological mechanism of all learning and memory.

Defining the presynaptic specialization is a cluster of synaptic vesicles ( ~40 nm diameter) containing neurotransmitters, some of which are closely associated with a thickening of the presynaptic plasma membrane, called the active zone.

Messages arrive at the synapse in the form of action potentials. Synaptic potential are triggered by action potentials; they in turn trigger subsequent action potential, continuing the neural message on to its destination.
What is synapse?

Cranial nerves

The 12 cranial nerves control motor and sensory functions of the head and neck, including innervation of voluntary and involuntary muscles and reception of general and special sensory information.

Because they merger from the cranium, they are called cranial nerves as opposed to spinal nerves that emerge from the spinal column.

The cranial nerves function as modified spinal nerves. As a group, they have both sensory and motor components: however, individual nerves may be purely sensory, purely motor, or mixed (both motor and sensory).

Twelve pairs of cranial nerves are peripheral nerves of the brain. The other pairs are nerves of the brainstem (and in one case, partially of the cervical spinal cord).

They supply structures of the head and neck and in the case of the vagus nerve, structures of the trunk.

The cranial nerves pass through or into the cranial bones and are numbered I to XII roughly in order from top to bottom.

Their functions are those of the head: some are concerned with awareness of, and communication with, the environment; and some are concerned with sustenance the gut tube and movements associated with it.
Cranial nerves