7th Cranial Nerve (Facial Nerve)

Dr D V Siva KumarAsso ProfessorGen Medicine

The facial nerve contains

- Motor fibers supplying the muscles of facial expression

- Visceral efferent (parasympathetic) fibers

- Visceral afferent (taste) fibers

Motor nucleus lies the lower pons medial to the descending nucleus and tract of the 5th cranial nerve. Axons from the motor nucleus wind around the nucleus of the 6th cranial nerve.

Anatomy of the Facial Nerve

The facial nerve and its visceral root (nervus intermedius) exit from the lateral aspect of the brain stem and cross the CP angle immediately adjacent to the 8th cranial nerve.

They enter the internal auditory meatus and passing through the facial canal of the temporal bone, lie in close proximity to the inner ear and tympanic membrane.

The facial nerves gives of several branches before exiting the skull through the stylomastoid foramen.

Visceral efferent arise in the superior salivary nucleus where as visceral afferent terminate in nucleus / tractus solitarius.

They run together as the nervous intermediates and acompany the facial nerve to the internal auditory meatus.

The parasympathetic fibers (visceral efferent) pass in the greater petrosal nerve to the splenopalatine ganglion and thence to the lacrimal gland to produce tears and in the chorda tympani nerve to the sub-mandibular ganglion

Anatomy of the Facial Nerve

The chorda tympani nerve contains both parasympathetic efferent and visceral afferent fibers.

Parasympathetic fibers are responsible for salivation.

Visceral afferent fibers convey sensations of taste from the anterior 2/3rd of the tongue.

Supra nuclear control of facial muscles :

Lower face muscles are controlled by contra lateral hemesphere

Upper face receive control from both hemespheres (bilateral representation), hence a lower motor neuron lesion paralyses all facial muscles on that side but an upper motor neuron lesion paralyses only the muscles in the lower half of the opposite side

Facial Weakness

Clinical Examination of the facial nerve :

Observe patient as he talks and smiles, watching for

- Eye closure

- Asymmetrical elevation of one corner of mouth

- Flattening of naso labial fold

Patient is then instructed to

- Wrinkle forehead (frontalis)

(by looking upwards)

- Close eyes by examiner attempts to open them (orbicularis oculi)

- Purse lips while examiner presses cheeks (buccinator)

- Show teeth (oribicularis oris)

Taste may be tested by using sugar, tartaric acid or sodium chloride. A small quantity of each substance is placed anteriorly on the appropriate side of the protruded tongue

In addition to examine for facial weakness and taste impairment also note whether the patient comments on reduced lacrimation or salivation on one side or hyper acusis (exaggeration of sounds due to loss of the stapedius reflex)

Def : Bell’s palsy is characterized by an acute paralysis of the face related to inflammation and swelling of the facial nerve within the facial canal or at the stylo mastoid foramen

It is usually unilateral rarely bilateral and may occur repetitively.

Family history is evident in some cases

Bell’s Palsy

Aetiology :

Uncertain

Viral infections (Herpes simplex, varicella zoster)

Epidemic of Bell’s Palsy

Part of syndrome of poly neuritis cranialis

Symptoms :

Pain over ipsi lateral mastoid precedes weakness which develops over a 48 hour period

Impairment of taste

Hyper acusis

Loss of salivation /Lacrimation

Bell’s Phenomenon – on attempting to close the eyes the one eye does not close and the eyeball rotates upwards and outwards.

Diagnosis :

Based on typical presentation and exclusion of

- Middle ear disease

- Diabetes

- Sarcoidosis

- Lyme disease

Treatment :

During the acute stage protect the exposed eye during sleep

Prednisolone given in high dosage in the acute stage (40 – 60 mg /day for 5 days) may reduce inflammation but there is no conclusive evidence of benefit.

Anti viral Therapy

Eye care (shielding) is important in preventing corneal abrasion

Prognosis :

Most patients (80%) recover in 4 to 8 wks. without treatment, in the remainder residual facial asymmetry may require corrective surgery

Incomplete paralysis indicates a good prognosis

In patients with complete paralysis, electrical absence of denervation on EMG is an optimistic sign.

Occasionally aberrant reinnervation occurs – movement of the angle of the mouth on closing the eyes (jaw winking) or lacrimation when facial muscles contract (crocodile tears)

Other facial nerve disorders :

Ramsay Hunt’s Syndrome

- Herpes Zoster infection of the geniculate ganglion

- Pain in the face

- Severe facial weakness

- Typical zoster vesicular eruption within the external auditory meatus

- Sero sanguinous discharge from the ear

- Deafness may result from 8th nerve involvement

- Cranial nerves from 5th to 12th are affected

Hemi facial spasm

- is characterised by unilateral clonic spasms beginning in the orbicularis oculi and spreading involve other facial muscles

- The stapedius muscle can be affected producing a subjective ipsilateral clicking sound.

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