5.1.4 Cranial Nerves XI and XII

Question 1

What fibres do the accessory and hypoglossal nerves carry? CNXI and XII

Answer 1

Motor only

Question 2

Outline the route of CNXI and XII

Answer 2

1. Medulla
2. Posterior cranial fossa
3. Jugular foramen
4. Carotid sheath (both leave superiorly in sheath)
5. Hypoglossal exits via hypoglossal canal and travels towards tongue, crosses ICA and ECA
6. Accessory exits and heads towards posterior triangle

Question 3

What does CNXII supply?

Answer 3

Muscles of the tongue

Question 4

How do you test CNXII?

Answer 4

Tongue movements (side to side)
Protrude the tongue

Question 5

How is the hypoglossal nerve damaged?

Answer 5

Surgery/pathology in proximity to or involving contents of upper carotid sheath, ICA and ECA e.g. carotid endartectomy

Posterior cranial fossa tumours

Brainstem medullary lesions

Motor neurone disease

Question 6

How do hypoglossal nerve lesions present?

Answer 6

Use genioglossal muscle
Deviates to side of lesion

Question 7

How do you test the accessory nerve?

Answer 7

Test actions of SCM- turn head against resistance

Trapezius- get them to shrug shoulders against resistance

Question 8

How can CNXI be damaged?

Answer 8

Injuries, surgery or pathology involving posterior triangle

Posterior cranial fossa tumours

Base of skull fractures involving the jugular foramen

Medullary lesions e.g. infarct

Question 9

Do lesions that affect CNXI cause paralysis of SCM?

Answer 9

SCM is innervated higher up than trapezius

If there is injury to the posterior triangle only trapezius will be affected as CNXI emerges deep to posterior border of SCM to enter posterior triangle