XII - Hypoglossal Nerve

Question 1

Outline the neuroanatomy of CN XII?

Answer 1

Is the 12th cranial nerve
> It has somatic motor function, innervating all the extrinsic and intrinsic muscles of the tongue (except the palatoglossus, innervated by vagus nerve).
> The hypoglossal nerve arises from the hypoglossal nucleus in the medulla oblongata of the brainstem.
> It comes out of mudulla oblongata between pyramids and the olives
> It crosses the dura matter and runs through the hypoglossal canal.

The hypoglossal nerve arises from the hypoglossal nucleus in the medulla oblongata of the brainstem. Located in front of nucleus gracilis, medial to dorsal nucleus of vagus, and posterior to medial longitudinal fasciculus

Question 2

Outline the course of CN XII

Answer 2

• deeply placed to IJV, ICA,9th, 10th, 11th nerve.
• then it will run in between ICA and ECA within carotid triangle.
• Then it will run deep to styloid process and deep to posterior belly of digastric muscle.
• And through mylohyoid muscle. And enter the sublingual region to supply the muscles of tongue.

Question 3

What are the functions of CN XII?

Answer 3

The hypoglossal nerve is responsible for motor innervation of the vast majority of the muscles of the tongue (except for p latesi m These muscles can be subdivided into two groups:
*Genioglossus (makes up the bulk of the tongue)
*Hyoglossus
* Styloglossus
*Palatoglossus (innervated by vagus nerve) ii) Intrinsic muscles
Superior longitudinal
Inferior longitudinal
Transverse
Vertical
Together, these muscles are responsible for all movements of the tongue.

Question 4

How do you examine CN XII?

Answer 4

Cranial Nerve Examination
> The hypoglossal nerve is examined by asking the patient to protrude their tongue.
> Other movements such as asking the patient to push their tongue against their cheek and feeling for the pressure on the opposite side of the cheek may also be used if damage is suspected.

Question 5

Describe CN XII palsy

Answer 5

Hypoglossal Nerve Palsy
> Damage to the hypoglossal nerve is a relatively uncommon cranial nerve palsy. Possible causes include head & neck malignancy and penetrating traumatic injuries. If the symptoms are accompanied by acute pain, a possible cause may be dissection of the internal carotid artery.
> Patients will present with deviation of the tongue towards the damaged side on protrusion, as well as possible muscle wasting and fasciculations (twitching of isolated groups of muscle fibres) on the affected side