Cranial Nerves

Question 1

General Inspection

Answer 1

• Look for obvious signs of facial weakness – e.g. flattening of the nasolabial folds.
• Strabismus – the eyes are not properly aligned caused by a defect in CN’s III, IV and VI.
• Bell’s palsy – inability to control facial muscles on the affected side caused by a defect in CNVII.
• Horner’s syndrome – damage to cervical sympathetic nerves gives a partial ptosis and involves both upper and lower lids leading to a small eye and miosis (small pupil) due to lack of iris innervation.

Question 2

Cranial Nerve I

Answer 2

Olfactory Nerve - Special Sensory

• Ask ‘have you noticed a change in your sense of smell recently?’ then shut 1 nostril and test smell.
• Ensure the patient does not simply have nasal congestion.
• Anosmia – patients complain of loss of taste – may be caused by damage to the olfactory filaments following a head injury or local invasion. Anosmia also occurs in Huntingdons and Parkinsons disease.
• Parosmia – pleasant odours perceived as unpleasant caused by trauma, sinus infection or SE of drugs.

Question 3

Cranial Nerve V Actions

Answer 3

Trigeminal Nerve has 3 main branches:

• V1 – Ophthalmic – somatic sensory – sensation from cornea, scalp, forehead, eyelid, nasal mucosa.
• V2 – Maxillary – somatic sensory – sensation from area overlying the maxilla and the upper jaw.
• V3 – Mandibular - somatic sensory – sensation from area overlying the mandible and lower jaw.
• Somatic motor – to muscles of mastication – temporalis, masseter and pterygoids.

Question 4

Cranial Nerve V Testing

Answer 4

• Ask to close eyes, touch V1, V2 and V3 with tissue and neurotip and tongue with orange stick.
• Ask patient to clench teeth and feel masseters then ask patient to open their jaw against resistance.
• Corneal reflex - patient looks upward, depress lower eyelid and touch lateral cornea - direct and consensual blinking.
• Jaw jerk - ask patient to let jaw hang open, percuss finger below lips, normal response is absent or just present.

Question 5

Cranial Nerve V Abnormalities

Answer 5

• Sensory – V1 - ophthalmic area touch above the medial aspect of the eyebrows, V2 – maxillary area touch the middle of the cheek and V3 – mandibular area touch below the lateral aspect of the lips
• Unilateral loss of sensation may result from direct injury from facial fracture or local cancer invasion.
• Corneal reflex – sensory arm is ophthalmic V1 and motor arm is facial nerve – lost in cancer invasion.
• Herpes zoster – re-activation of herpes varicella zoster (chicken pox) commonly affects ophthalmic area.
• A brisk jaw jerk occurs with bilateral upper motor neurone lesion above the level of the pons

Question 6

Cranial Nerve VII Actions

Answer 6

Facial Nerve:

• Somatic motor – to the muscles of facial expression and the scalp.
• Special sensory – taste from anterior 2/3 of the tongue and palate (via chorda tympani branch)
• Visceral motor – PNS innervations of submandibular and sublinguinal salivary and lacrimal glands.

Question 7

Cranial Nerve VII Testing

Answer 7

• Ask patient to wrinkle forehead, bear teeth, open eyes against resistance and blow out cheeks.
• Ask to extend tongue and use cotton buds dipped in salt, sugar, sour, bitter with rinses in between.

Question 8

Cranial Nerve VII Abnormalities

Answer 8

• Motor – inspect face, eye opening/closing for symmetry, watch for spontaneous/involuntary moves.
• Unilateral lower motor neurone lesion – weakness of both upper and lower facial muscles
• Unilateral upper motor neurone lesion – weakness in lower facial muscles with relative sparing of upper facial muscles due to bilateral cortical innervation of the upper facial muscles – the nasolabial fold may flattened and the corner of the mouth may droop but eye closure is usually well preserved.

Question 9

Cranial Nerve VIII

Answer 9

Vestibulocochlear Nerve:

• Vestibular – sensation from semicircular ducts and cochlear – hearing from the spiral organ.
• Test with Weber and Rinne’s.

Question 10

Cranial Nerve IX

Answer 10

Glossopharyngeal Nerve:

• Somatic motor – to the stylopharyngeus to assist with swallowing.
• Somatic sensory – cutaneous sensation from the external ear.
• Visceral motor - PNS innervation of the parotid gland.
• Visceral sensory – sensation from parotid gland, carotid body and sinus, pharynx and middle ear.
• Special sensory – taste from the posterior 1/3 of the tongue.

Question 11

Cranial Nerve X

Answer 11

Vagus Nerve:

• Somatic motor – to pharynx, intrinsic larynx and palate muscles and superior 2/3 of oesophagus.
• Somatic sensory – sensation from auricle, external acoustic meatus and dura mater.
• Visceral motor – PNS innervation to trachea, bronchi, GI tract and cardiac smooth muscle.
• Visceral sensory – tongue, pharynx, larynx, trachea, bronchi, heart, GI tract to left colic flexure.
• Special sensory – taste from the epiglottis and the palate.

Question 12

Cranial Nerves IX and X Testing

Answer 12

• Ask the patient to say ‘British constitution’ and ‘aah’ with an open mouth whilst viewing uvula with torch.
• Ask patient to puff out cheeks and feel for air leaving nose, cough and assess the strength of the cough and perform the water swallow test – look for absent swallow or a cough.

Question 13

Cranial Nerve IX and X Abnormalities

Answer 13

• Assess the patients speech for dysarthia or dysphonia – nasal quality may suggest palatal paralysis.
• Damage to the recurrent laryngeal branch of CNX due to lung malignancy, thyroid surgery, mediastinal tumours and aortic arch aneurysm causes dysphonia and a ‘bovine’ cough.
• Abnormal word articulation – can be caused by a defect in any of CNV, CNVII, CNX or CNXII.
• Assessment of the uvula both at rest and when the patient says ‘ah’ – deviation is away from the lesion.
• If the movement of the palate is weak it doesn’t occlude the nasopharynx when cheeks are blown out.
• Water swallow test – observe for absent swallow, cough or delayed cough or change in voice.
• Can elicit the gag reflex by touching the soft palate – afferent arm is CNIX and efferent arm is CNX.

Question 14

Cranial Nerve XI

Answer 14

Accessory Nerve - somatic motor to sternocleidomastoid and trapezius.

• Palpate and assess SCM and trapezius and ask to shrug and turn their head against resistance.
• Inspect for wasting or hypertrophy and palpate to assess bulk and symmetry.
• Can be damaged during surgery in posterior triangle penetrating injuries or local tumour invasion.
• SCM wasting characteristic of dystrophia myotonica and head drop is seen in MG, MND and myopathies.

Question 15

Cranial Nerve XII

Answer 15

Hypoglossal Nerve - to the intrinsic and extrinsic muscles of the tongue.

• Inspect tongue at rest and when protruded, ask patient to move from side to side to test power.
• Inspect tongue for wasting, fasciculation, involuntary movements and for deviation when protruded.
• Unilateral lower motor XII nerve lesion lead to wasting on that side and deviation towards that side.
• Bilateral lower motor XII nerve lesion lead to increased tone (spastic) and an acorn like appearance.
• When associated with lesions of IX, X and XI typically in MND this is known as bulbar palsy.