Corneal reflex

Routine testing of the corneal reflex is unnecessary, but may

be relevant when the history suggests a lesion localising to

the brainstem or cranial nerves V, VII or VIII. The afferent limb

is via the trigeminal nerve, the efferent limb via the facial

nerve.

• Explain to the patient what you are going to do and ask

them to remove their contact lenses, if relevant.

• Gently depress the lower eyelid while the patient looks up.

• Lightly touch the lateral edge of the cornea with a wisp of

damp cotton wool (Fig. 7.7).

• Look for both direct and consensual blinking.

Fig. 7.7 Testing the corneal reflex. The cotton-wool wisp should touch

the cornea overlying the iris, not the conjunctiva, and avoid visual stimulus.

Fig. 7.8 Eliciting the jaw jerk.

7.5 Comparison of bulbar and pseudobulbar palsy

Bulbar palsy Pseudobulbar palsy

Level of motor lesion Lower motor

neurone

Upper motor neurone

Speech Dysarthria Dysarthria and dysphonia

Swallowing Dysphagia Dysphagia

Tongue Weak, wasted

and fasciculating

Spastic, slow-moving

Jaw jerk Absent Present/brisk

Emotional lability Absent May be present

Causes Motor neurone

disease

Cerebrovascular disease,

motor neurone disease,

multiple sclerosis

130 • The nervous system

from the lateral pontomedullary junction in close association with

the VIII nerve (Fig. 7.11); together they enter the internal acoustic

meatus (see Fig. 7.5). At the lateral end of the meatus the VII

nerve continues in the facial canal within the temporal bone,

exiting the skull via the stylomastoid foramen. Passing through

the parotid gland, it gives off its terminal branches. In its course

in the facial canal it gives off branches to the stapedius muscle

and its parasympathetic fibres, as well as being joined by the

taste fibres of the chorda tympani (see Fig. 7.10).

Examination sequence

Examination is usually confined to motor function; taste is

rarely tested.

Motor function

• Inspect the face for asymmetry or differences in blinking or

eye closure on one side. Note that minor facial asymmetry

is common and rarely pathological.

• Watch for spontaneous or involuntary movement.

• For the following actions it is often easiest to demonstrate

the actions yourself and ask the patient to copy you,

observing for any asymmetry.

• Ask the patient to raise their eyebrows and observe for

symmetrical wrinkling of the forehead (frontalis muscle).

• Ask the patient to screw their eyes tightly shut and resist

you opening them (orbicularis oculi).

• Ask the patient to bare their teeth (orbicularis oris).

• Ask the patient to blow out their cheeks with their mouth

closed (buccinators and orbicularis oris).

Sensory symptoms include facial numbness and pain. Unilateral

loss of sensation in one or more branches of the V nerve may

result from direct injury in association with facial fractures

(particularly V2), local invasion by cancer or Sjögren’s syndrome.

Lesions in the cavernous sinus often cause loss of the corneal

reflex and V1 or V2 cutaneous sensory loss. Cranial nerves III, IV

and VI may also be involved (see Fig. 8.3). Trigeminal neuralgia

causes severe, lancinating pain, typically in the distribution of V2

or V3. Reactivation of herpes varicella zoster virus (chickenpox)

can affect any sensory nerve, but typically either V1 or a thoracic

dermatome (Fig. 7.9). In herpes zoster ophthalmicus (affecting V1)

there is a risk of sight-threatening complications. Hutchinson’s

sign, vesicles on the side or tip of the nose, may be present.

Clinically significant weakness of the muscles of mastication

is unusual but may occur in myasthenia gravis, with fatigable

chewing.

Facial (VII) nerve

The facial nerve supplies the muscles of facial expression (frontalis,

orbicularis oculi, buccinators, orbicularis oris and platysma) and

carries parasympathetic fibres to the lacrimal, submandibular and

sublingual salivary glands (via nervus intermedius). It receives

taste sensation from the anterior two-thirds of the tongue (via

the chorda tympani; Fig. 7.10).

Anatomy

From its motor nucleus in the lower pons, fibres of the VII nerve

pass back to loop around the VI nerve nucleus before emerging

A B C

D

Fig. 7.9 Herpes zoster. A The ophthalmic division of the left trigeminal (V) nerve is involved. B The maxillary division of the left V nerve. C Cervical

spinal root left C5. D Thoracic spinal root right T8.

Cranial nerves • 131

7

angle tumours (including acoustic neuroma), trauma and

parotid tumours. Synkinesis (involuntary muscle contraction

accompanying a voluntary movement: most commonly, twitching

of the corner of the mouth with ipsilateral blinking) is a sign of

aberrant reinnervation and may be seen in recovering lower

motor neurone VII lesions.

In unilateral VII nerve upper motor neurone lesions, weakness

is marked in the lower facial muscles with relative sparing of the

upper face. This is because there is bilateral cortical innervation

of the upper facial muscles. The nasolabial fold may be flattened

and the corner of the mouth drooped, but eye closure is

usually preserved (Fig. 7.12B). Hemifacial spasm presents with

synchronised twitching of the ipsilateral eye and mouth.

Bilateral facial palsies are less common, but occasionally occur,

as in Guillain–Barré syndrome, sarcoidosis, or infection such as

Lyme disease, HIV or leprosy. Facial weakness, especially with

respect to eye closure, can also be found in some congenital

myopathies (facioscapulohumeral or myotonic dystrophies).

Distinct from VII nerve palsies, Parkinson’s disease can cause loss

of spontaneous facial movements, including a slowed blink rate,

and involuntary facial movements (levodopa-induced dyskinesias)

may complicate advanced disease.

Involuntary emotional movements, such as spontaneous

smiling, have different pathways and may be preserved in the

presence of paresis.

Vestibulocochlear (VIII) nerve

See page 173.

Glossopharyngeal (IX) and vagus (X) nerves

The IX and X nerves have an intimate anatomical relationship.

Both contain sensory, motor and autonomic components. The

glossopharyngeal (IX) nerve mainly carries sensation from the

pharynx and tonsils, and sensation and taste from the posterior

one-third of the tongue. The IX nerve also supplies the carotid

chemoreceptors. The vagus (X) nerve carries important sensory

In a unilateral lower motor neurone VII nerve lesion, there is

weakness of both upper and lower facial muscles. Bell’s palsy

is the term used to describe an idiopathic acute lower motor

neurone VII nerve paralysis, often preceded by mastoid pain. It

may be associated with impairment of taste and hyperacusis

(high-pitched sounds appearing unpleasantly louder than normal).

Bell’s phenomenon occurs when a patient closes their eyes:

as eye closure is incomplete the globe can be seen to roll

upwards, to avoid corneal exposure (Fig. 7.12A). Ramsay Hunt

syndrome occurs in herpes zoster infection of the geniculate (facial)

ganglion. This produces a severe lower motor neurone facial