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Hypoglossal nucleus

The hypoglossal nucleus is a somatic motor cranial nerve nucleus located in the dorsal medulla oblongata. It gives rise to motor fibers of the hypoglossal nerve (cranial nerve XII), which innervates the intrinsic and extrinsic muscles of the tongue. This nucleus is essential for voluntary tongue movements involved in speech, mastication, and swallowing.

Because of its fixed midline position and close relationship to the fourth ventricle, the hypoglossal nucleus is an important landmark in brainstem anatomy and neuroimaging.

Synonyms

  • Nucleus of hypoglossal nerve

  • CN XII motor nucleus

Location

  • Located in the dorsal medulla oblongata

  • Positioned close to the midline

  • Forms the hypoglossal trigone on the floor of the fourth ventricle

  • Extends longitudinally through the medulla

  • Anterior to the fourth ventricle

  • Posterior to the medial lemniscus and pyramids

Anatomical organization

  • Somatic efferent motor nucleus

  • Columnar arrangement extending rostrocaudally

  • Motor neurons give rise to hypoglossal nerve rootlets

  • Fibers course ventrally and laterally through the medulla

Relations

Anteriorly:

  • Medullary pyramids

Posteriorly:

  • Fourth ventricle

  • Hypoglossal trigone

Medially:

  • Median raphe

Laterally:

  • Dorsal motor nucleus of the vagus

  • Nucleus solitarius

Nerves originating from the nucleus

  • Hypoglossal nerve (cranial nerve XII):

    • Pure motor nerve

    • Rootlets emerge from the preolivary sulcus between the pyramid and olive

    • Supplies intrinsic and extrinsic tongue muscles (except palatoglossus)

Function

  • Tongue movement: Controls intrinsic tongue shaping and positioning

  • Speech articulation: Essential for precise phonation

  • Swallowing: Coordinates tongue propulsion during the oral phase

  • Mastication assistance: Helps manipulate food bolus

MRI appearance (normal)

T1-weighted images:

  • Hypoglossal nucleus: Isointense to surrounding gray matter

T2-weighted images:

  • Normal nucleus: Isointense to adjacent brainstem gray matter

FLAIR:

  • Normal: Inconspicuous; blends with surrounding medullary gray matter

Diffusion-weighted imaging (DWI):

  • Normal: No diffusion restriction

Post-contrast T1-weighted images:

  • Normal: No enhancement

CT appearance (normal)

Non-contrast CT:

  • Hypoglossal nucleus: Not individually visualized

MRI image

MRI Hypoglossal nucleus axial anatomy image -img-00000-00000