Other cranial nerves

Published on 10/04/2015 by admin

Filed under Neurology

Last modified 10/04/2015

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Other cranial nerves

Face, motor and sensory

Trigeminal nerve (5th)

Facial sensation is supplied by the trigeminal nerve (Fig. 1), which has three branches:

1. The ophthalmic, supplying forehead to vertex and tip of the nose, and including the cornea.
2. The maxillary, supplying the cheek to the angle of the jaw and the inner aspect of the mouth and upper palate.
3. The mandibular, supplying the lower jaw but not the angle of the jaw.
image

Fig. 1 Facial sensation is supplied by the trigeminal (V) nerve.

The sensation to pinprick, light touch and temperature can be tested in each division. The afferent component of the corneal reflex is the ophthalmic branch of the trigeminal nerve.

Trigeminal motor function is rarely abnormal. This can be tested by getting the patient to clench the teeth and feeling the masseter and temporalis.

Facial nerve (7th)

Look at the patient’s face for asymmetries. Compare the blink rate.

To test facial nerve function, ask the patient to look up at the ceiling (look at the frontalis), screw up the eyes (look at the orbicularis oculi), to whistle and show the teeth. Three patterns of abnormality are seen (Fig. 2):

1. Lower motor neurone (LMN) 7th: all facial muscles are affected. If severe, the patient is unable to close the eye and the eye is seen to roll up on attempted closure (Bell’s phenomenon) (common cause is Bell’s palsy; see Box 1). Reduced blink rate.
2. Upper motor neurone 7th: relative sparing of the frontalis.
3. Extrapyramidal weakness: limited spontaneous movement, full voluntary movement.
image

Fig. 2 Facial nerve lesion. (a) Right-sided lower motor neurone weakness; note droopy mouth, loss of nasolabial fold and eyebrow lines; (b) right-sided upper motor neurone lesion; note weakness in lower face with sparing of forehead muscles – especially when asked to look up.

Box 1 Bell’s palsy

This is a common condition (25 per 100 000 per year) of unknown aetiology. The patient develops a unilateral facial weakness, often with pain behind the ear, altered taste on one side of the tongue and hyperacusis. It usually improves spontaneously, but patients may be left with some facial weakness or aberrant renervation. Early treatment with oral steroids hastens and improves recovery. The evidence for the use of the antivirals, aciclovir or valaciclovir, is less clear cut. It is important to protect the cornea from trauma and abrasions (artificial tears, patching eye closed).

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