Hypoglossal nerve (CN XII)
Nerve · CN XII Motor
From the hypoglossal nucleus in the floor of the fourth ventricle it emerges as rootlets between the pyramid and the olive, leaves through the hypoglossal canal, descends between the internal carotid artery and internal jugular vein, then loops forward across the carotid bifurcation and the lingual artery, above the hyoid, into the tongue. Purely motor to all intrinsic and extrinsic tongue muscles except palatoglossus.
Traced from the start
- Medulla oblongata
- Hypoglossal nerve (CN XII)
Detail
- Motor
- Intrinsic tongue muscles plus genioglossus (protrusion), hyoglossus and styloglossus; not palatoglossus (vagus)
- Hitch-hikers
- C1 fibres travel with it to geniohyoid and thyrohyoid and leave as the superior root of the ansa cervicalis; these are not hypoglossal fibres
- Test
- Inspect the resting tongue for wasting and fasciculation, then protrude it and push it into each cheek against resistance
When it goes wrong
Lower motor neurone lesion: skull base tumour or fracture, carotid endarterectomy, submandibular or carotid body surgery, jugular foramen extension (Collet–Sicard), motor neurone disease
Tongue deviates towards the weak side on protrusion because the healthy genioglossus pushes it across, with ipsilateral wasting and fasciculation
Upper motor neurone lesion in the internal capsule or bilateral corticobulbar tracts (pseudobulbar palsy)
Tongue deviates away from the lesion without wasting; when bilateral it is small, spastic and slow with a brisk jaw jerk and emotional lability
Practise this structure
4 questions in the bank tagged Cranial Nerves.
A 52-year-old woman has had two months of numbness over the right forehead, the right upper eyelid and the tip of her nose, with a gritty feeling in the right e…
Foundations · middle twist
A 44-year-old man has had 18 months of worsening hearing on the left with constant ringing in that ear. He still follows conversation in a quiet room but cannot…
Foundations · middle twist
A 58-year-old man has sudden vertigo and a hoarse voice, and chokes when he drinks. The palate elevates to the right and there is no gag response when the left…
Foundations · middle twist
A 27-year-old man was struck on the head at football a week ago. He now sees two images, one above the other, worst when reading or going down stairs. The verti…
Foundations · middle twist