The facial nerve is the seventh cranial nerve. It contains the motor, sensory, and parasympathetic (secretomotor) nerve fibers, which provide innervation to many areas of the head and neck region.

There are numerous causes of facial nerve disorder:

• Trauma such as birth trauma, skull base fractures, facial injuries, middle ear injuries, or surgical trauma.
• Nervous system disease including stroke involving the brain stem.
• Infection of the ear or face, or herpes zoster of the facial nerve (Ramsay Hunt syndrome)

Damage to the facial nerve can result in a distorted appearance to your face. You can have difficulty making a certain facial expression or problems closing your eyes. The facial muscles will often sag or droop so your face feels stiff.

Preganglionic parasympathetic neurons reside in the inferior salivary nucleus in the medulla and travel over the glossopharyngeal nerve, or cranial nerve IX.

The facial nerve is the 7th cranial nerve and carries nerve fibers that control facial movement and expression. The facial nerve also carries nerves that are involved in taste to the anterior 2/3 of the tongue and producing tears (lacrimal gland).

What are the symptoms of facial paralysis?

• facial paralysis on one side (rarely are both sides of the face affected)
• loss of blinking control on the affected side.
• decreased tearing.
• drooping of the mouth to the affected side.
• altered sense of taste.
• slurred speech.
• drooling.
• pain in or behind the ear.

Four signs of facial nerve injury

• Pain. Often compared to an electrical shock, nerve (neuropathic) pain is a shooting, stabbing, or burning discomfort in areas linked to the distribution of the damaged nerve.
• Hypersensitivity or decreased sensation.
• Loss of taste.
• Loss of facial muscle movement.

Doctors use an MRI to examine the entire facial nerve. This imaging test also allows a doctor to identify swelling or a growth on or near the nerve. Your doctor may recommend a type of MRI that uses a contrast agent, or dye, called gadolinium.

The parasympathetic nerves are autonomic or visceral branches of the peripheral nervous system (PNS). Parasympathetic nerve supply arises through three primary areas: The parasympathetic ganglion where these preganglionic neurons synapse will be close to the organ of innervation.

When a stressor begins, epinephrine and norepinephrine are released from the adrenal medulla and norepinephrine is released from the sympathetic nerve terminals. Because the secretory cells are neurons, catecholamine release is very quick and effects can be seen in less than a second.

The parasympathetic fibres of the chorda tympani stay with the lingual nerve, but the main body of the nerve leaves to innervate the anterior 2/3 of the tongue. The parasympathetic fibres of the facial nerve are carried by the greater petrosal and chorda tympani branches.

Only the motor function of the facial nerve is affected, therefore resulting in paralysis or severe weakness of the muscles of facial expression. There are various causes of extracranial lesions of the facial nerve: Parotid gland pathology – e.g a tumour, parotitis, surgery. Infection of the nerve – particularly by the herpes virus.

Specifically, the parasympathetic nervous system cranially is concerned with three of the cranial nerves, which will be dealt with in turn in greater detail throughout this book. The cranial nerves involved in the parasympathetic nervous system are the oculomotor, facial, glossopharyngeal, and vagus nerves.

Extracranial lesions occur during the extracranial course of the facial nerve (distal to the stylomastoid foramen). Only the motor function of the facial nerve is affected, therefore resulting in paralysis or severe weakness of the muscles of facial expression. There are various causes of extracranial lesions of the facial nerve: