7 th cranial nerve (facial nerve) dr d v siva kumar asso professor gen medicine
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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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