5.1.2 Cranial Nerve VII

Question 1

What fibres does the facial nerve carry?

Answer 1

Motor
Speical sensory (taste)
Parasympathetic

Question 2

What do each of the fibres of CNVII supply?

Answer 2

Motor
- Muscles of facial expression
- Stapedius

Special sensory
- Anterior 2/3 of tongue

Parasympathetic
- Lacrimal glands
- Mucus glands
- Salviary, except parotid

Question 3

How do you test the facial nerve?

Answer 3

Muscles of facial expression, ask about sense of taste etc. will be very vague, mainly go off motor

Question 4

What are some signs of CNVII lesions?

Answer 4

Unilateral facial droop +/- change in sense of taste, dry eyes, dry mouth etc.

Question 5

What are some causes of facial nerve lesions?

Answer 5

• Lesions in/around internal acoustic meatus
• Posterior cranial fossa tumours
• Middle ear disease
• Inflammation in facial canal (Bell’s palsay, Ramsay- Hunt Syndrome)
• Parotid disease

Question 6

What is the route of the facial nerve?

Answer 6

1)Pons

2)Internal accoustic meatus to enter the petrous bone

3)Geniculate ganglion

4)Three intracranial branches:
- Greater petrosal comes off first
- Nerve to stapedius
- Chorda tympani

5)Extracranial branch emerges through stylomastoid foramen at base of the skull, runs through parotid gland then you get 5 main branches

(Geniculate ganglion is the first thing in petrous bone)

Question 7

What is Ramsay-Hunt syndrome?

Answer 7

Varicella Zosta causes facial droop, vesicles will be present on the external ear

Question 8

What do the 3 intracranial branches of the facial nerve do?

Answer 8

Nerve to stapedius innervates stapedius causing it to contract to dampen vibrations of stapes

Greater petrosal
Carries parasympathetic fibres to lacrimal and nasal mucosal glands (think greater, so at the top, innervates glands at the top of the face)

Chorda tympani
Taste from anterior 2/3 tongue
Carries parasympathetics to all salivary glands except for parotid

Question 9

How can you tell the difference between stroke and a lesion of the facial nerve?

Answer 9

Look back at 4.1.3 if struggling to understand

Stroke
Facial nerve has two supplies, ipsilateral and contralateral, contralateral is the dominant supply

In a stroke the contralateral side is damaged so the ipsilateral side acts as back up

Ipsilateral side does not provide back up for the lower half of the face, but the top half of the face will be unaffected

Patient will therefore be able to use muscles of facial expression in top half of the face but not in the bottom

Lesion
In a lesion the brainstem itself is affected, therefore there is not back up from the ipsilateral side, so the entire ipsilateral side of the face will have facial expression paralysis