Fig. 7.6 The sensory distribution of the three divisions of the

trigeminal nerve. 1, Ophthalmic division. 2, Maxillary division.

3, Mandibular division.

Olfactory nerves

(cribriform plate)

Ophthalmic division of

trigeminal nerve

(superior orbital fissure)

Maxillary division of

trigeminal nerve

(foramen rotundum)

Trigeminal ganglion in

Meckel's cave

Trigeminal nerve (motor root)

Glossopharyngeal

nerve

Vagus nerve

Spinal accessory

nerve

(Jugular

foramen)

Hypoglossal nerve (hypoglossal canal)

Optic nerve (optic canal)

Oculomotor nerve

Trochlear nerve

Superior

orbital

fissure

Mandibular division of trigeminal

nerve (foramen ovale)

Facial and

vestibulocochlear nerves

(internal acoustic meatus)

Abducens nerve (inferior petrosal sinus)

Anterior cranial fossa

Middle cranial fossa

Posterior cranial fossa

Fig. 7.5 Base of the cranial cavity. The dura mater, with the cranial nerves and their exits from the skull. On the right side, part of the tentorium

cerebelli and the roof of the trigeminal cave have been removed.

Hyposmia or anosmia (reduction or loss of the sense of

smell) may result from upper respiratory infection, sinus

disease, damage to the olfactory filaments after head injury or

infection, local compression (by olfactory groove meningioma,

for example; see Fig. 7.29C) or invasion by basal skull

tumours. Disturbance of smell may also occur very early in

Parkinson’s and Alzheimer’s diseases. Patients often note

hypogeusia/ageusia (altered taste) with anosmia too, as taste

is crucially influenced by the sense of smell.

Parosmia is the perception of pleasant odours as

unpleasant; it may occur with head trauma or sinus

infection, or be an adverse effect of drugs. Olfactory

hallucinations may occur in Alzheimer’s disease and focal

epilepsies.

Optic (II), oculomotor (III), trochlear (IV)

and abducens (VI) nerves

See Chapter 8.

Trigeminal (V) nerve

The V nerve conveys sensation from the face, mouth and part of

the dura, and provides motor supply to the muscles of mastication.

Anatomy

The cell bodies of the sensory fibres are located in the trigeminal

(Gasserian) ganglion, which lies in a cavity (Meckel’s cave) in

the petrous temporal dura (see Fig. 7.5). From the trigeminal

Cranial nerves • 129

7

Jaw jerk

• Ask the patient to let their mouth hang loosely open.

• Place your forefinger in the midline between lower lip and

chin.

• Percuss your finger gently with the tendon hammer in a

downward direction (Fig. 7.8), noting any reflex closing of

the jaw.

• An absent, or just present, reflex is normal. A brisk jaw

jerk occurs in pseudobulbar palsy (Box 7.5).

The ophthalmic branch leaves the ganglion and passes forward

to the superior orbital fissure via the wall of the cavernous sinus

(see Fig. 8.3). In addition to the skin of the upper nose, upper

eyelid, forehead and scalp, V1 supplies sensation to the eye

(cornea and conjunctiva) and the mucous membranes of the

sphenoidal and ethmoid sinuses and upper nasal cavity.

The maxillary branch (V2) passes from the ganglion via the

cavernous sinus to leave the skull by the foramen rotundum.

It contains sensory fibres from the mucous membranes of

the upper mouth, roof of pharynx, gums, teeth and palate

of the upper jaw and the maxillary, sphenoidal and ethmoid

sinuses.

The mandibular branch (V3) exits the skull via the foramen ovale

and supplies the floor of the mouth, sensation (but not taste)

to the anterior two-thirds of the tongue, the gums and teeth of

the lower jaw, mucosa of the cheek and the temporomandibular

joint, in addition to the skin of the lower lips and jaw area, but

not the angle of the jaw (see Fig. 7.6).

The motor fibres of V run in the mandibular branch (V3) and

innervate the muscles of mastication: temporalis, masseter and

medial and lateral pterygoids.

Examination sequence

Four aspects need to be assessed: sensory, motor and two

reflexes.

Sensory

• Ask the patient to close their eyes and say ‘yes’ each time

they feel a light touch (you use a cotton-wool tip for this

test). Do this in the areas of V1, V2 and V3.

• Repeat using a fresh neurological pin, such as a Neurotip,

to test superficial pain.

• Compare both sides. If you identify an area of reduced

sensation, map it out. Does it conform to the distribution

of the trigeminal nerve or branches? Remember the angle

of the jaw is served by C2 and not the trigeminal nerve,

but V1 extends towards the vertex (see Fig. 7.6).

• ‘Nasal tickle’ test: use a wisp of cotton wool to ‘tickle’ the

inside of each nostril and ask the patient to compare. The

normal result is an unpleasant sensation easily appreciated

by the patient.

Motor (signs rare)

• Inspect for wasting of the muscles of mastication (most

apparent in temporalis).

• Ask the patient to clench their teeth; feel the masseters,

estimating their bulk.

• Ask the patient to open their jaw and note any deviation;

the jaw may deviate to the paralysed side due to

contraction of the intact contralateral pterygoid muscle.