Disorders of the Cranial Nerves

Question 1

What are the names and functions of the 12 cranial nerves?

Answer 1

Olfactory - Smell

Optic - Vision

Occulomotor - Eye movements

Trochlear - Superior Oblique muscle

Trigeminal - Opthalmic, Maxillary, Mandibular

Abducens - Lateral rectus muscle

Facial - Muscle of fascial expression, Taste of anterior 2/3 tongue

Vestibulocochlear - Hearing and Balance

Glossopharyngeal - Taste and general sensation posterior 1/3 tongue

Vagus - Innervation of abdominal organs

Accessory - Innervate SCM and Trapezius muscle

Hypoglossal - Movement of tongue

Question 2

What are the clinical tests used to assess cranial nerve function?

Answer 2

Olfactory – identify strong smells

Optic – vision test using Snell chart, peripheral fields, shine light in eye test

Oculomotor – accommodation, tracking finger test, shine light in eye test

Trochlear – Tracking finger test

Trigeminal – cotton wool and pin prick test on forehead, check and chin, push jaw down against my hand, jaw jerk

Abducens – tested in oculomotor section

Facial – repeat my facial expressions

Vestibulocochlear – whispered hearing test, rinne’s and weber’s test

Glossopharyngeal – Gag-reflex, cough

Accesory – push your shoulders up against my hands and turn your head to show SCM

Hypoglossal – say the days of the week, wiggle your tongue around

Question 3

What are the various cranial nerve reflexes that are tested?

Answer 3

Pupillary light reaction

afferent – II ; efferent – III

Corneal reflex

afferent – V ; efferent – VII

Jaw jerk

afferent and efferent – V

Gag reflex

afferent – IX ; efferent - X

Question 4

What are the causes of small and dilated pupils?

Answer 4

Small pupils - Activation of parasympathetic supply to the intrinsic muscles of the eye, bright lights, Horners

Dilated pupils - Sympathetic activation, dark conditions, anxiety

Question 5

What are the causes of eye movement disorders?

Answer 5

3^rd nerve palsy (oculomotor) caused by hypertension, diabetes, artery aneurysm

4^th nerve palsy (trochlear)

6^th nerve palsy (abducens) caused by diabetes, meningitis

Nystagmus

Question 6

What are the clinical features of trigeminal neuralgia, Bell’s Palsy and Vestibular Neuronitis?

Answer 6

Trigeminal neuralgia - Paroxysmal attacks of lancinating pain

Bell’s palsy – Unilateral facial weakness, preceded by pain behind ear, eye closure affected, forhead included so LMN

Vestibular neuronitis – sudden onset, disabling vertigo, vomiting

Question 7

What are the clinical features of pseudobulbar and bulbar palsy?

Answer 7

Pseudobulbar Palsy (Bilateral UMN Lesion):

• Difficulty swallowing (dyshpagia)
• Difficulty speaking (dysphonia)
• Difficult articulation of speach (dysarthria)
• Immobile tongue
• Brisk jaw jerk reflex

Bulbar Palsy (Bilateral LMN lesion):

• Wasted, fasciculating tongue
• Dysarthria
• Dysphonia
• Dysphagia

Question 8

What are the locations of the cranial nerve nuclei?

Answer 8

Midbrain - 3 & 4

Pons - 5, 6 & 7

PontoMedullary Junction - 8

Medulla - 9, 10, 11, 12

Question 9

By which mechanisms can cranial nerves be damaged?

Answer 9

Within the brain – due to ischaemia or tumour

Crossing the sub-arachnoid space – meningitis

Outside the skull – base of skull tumours arising in nasopharynx

Question 10

How can cranial nerve signs indicate various pathologies, not limited to cranial nerve lesions?

Answer 10

Stroke:

• Eye movement disorders
• Facial weakness
• Difficulty swallowing

Thyroid disease - double vision

Question 11

What are the effects of sympathetic and parasympathetic systems on pupillary responses?

Answer 11

Sympathetic:

• Activates the pupillary dilater muscle of the eye, causing the pupil to dilate
• Damage anywhere in the sympathetic pathway could lead to a constricted pupil

Parasympathetic:

• Activates the pupillary constrictor muscle, causing the pupil to constrict
• Loss of parasympathetic supply results in a constantly dilated pupil, e.g. 3rd nerve palsy