Nervous system · Head and neck

Cranial nerve nuclei !

The cranial nerve nuclei are clusters of nerve cells in the brainstem where the cranial nerves start or end; they explain which nerves fail together in strokes.

Official name: Nucleus of oculomotor nerve

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What it is

Clusters of nerve cells in the brainstem where the cranial nerves start or end.

What it does

Explain which nerves fail together in brainstem strokes.

Key facts

Where

Midbrain: III, IV; pons: V, VI, VII, VIII; medulla: IX, X, XII (XI in the upper cervical cord)

Function

Motor nuclei lie near the midline, sensory ones laterally; brainstem strokes combine a cranial nerve sign with opposite-side limb signs

Relations

Behind

Many lie under the floor of the fourth ventricle: the facial colliculus (abducens nucleus), the hypoglossal and vagal trigones and the vestibular area

In front

Descending corticospinal fibres in the base of the brainstem, which is why lesions combine cranial nerve and limb signs

Contents

Midbrain: oculomotor, Edinger–Westphal, trochlear; pons: trigeminal motor and main sensory, abducens, facial, salivatory, vestibular and cochlear; medulla: ambiguus, solitary, dorsal vagal, hypoglossal

Examination

• Pupils and eye movements: oculomotor, trochlear and abducens nuclei, linked by the medial longitudinal fasciculus
• Corneal reflex and facial movement: trigeminal and facial nuclei in the pons
• Gag reflex, palate elevation and voice: nucleus ambiguus and the glossopharyngeal and vagus nerves
• Tongue protrusion: deviation toward the weak side in a hypoglossal nucleus or nerve lesion

On imaging

The nuclei are not seen one by one on routine imaging. MRI (axial T2, FLAIR, DWI) finds a brainstem lesion and the nucleus is inferred from its level: midbrain for III and IV, pons for V to VIII, medulla for IX to XII. On the floor of the fourth ventricle, the facial colliculus marks the abducens nucleus. CT shows the brainstem poorly.

Clinical notes

• Matching the cranial nerve sign to its nucleus gives the level: oculomotor (Weber, midbrain), abducens and facial (Millard–Gubler, pons), hypoglossal (medial medulla), ambiguus (lateral medulla)
• A lesion of the spinal trigeminal nucleus in the lateral medulla removes pain and temperature from the same side of the face
• The four vestibular nuclei (superior, lateral or Deiters, medial, inferior) lie under the vestibular area; lateral medullary (Wallenberg) infarcts hit them: vertigo, nystagmus and falling toward the lesion

Development

As in the spinal cord, a groove (sulcus limitans) separates the motor basal plate from the sensory alar plate. When the fourth ventricle opens, the plates fold outward, so in its floor motor nuclei lie medial and sensory nuclei lateral.

Memory aid

Rule of 4: four cranial nerves above the pons (I–IV), four in the pons (V–VIII), four in the medulla (IX–XII); the four motor nerves that divide evenly into 12 (III, IV, VI, XII) have nuclei near the midline.

Related conditions

• Benign paroxysmal positional vertigo (BPPV)

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Educational information, not medical advice. For any symptom, see a health professional.

Its names

Official Latin (TA2)

nucleus nervi oculomotorius TA2 5892

Official Spanish (DeCS)

Núcleos de los nervios craneales

English (TA2)

Nucleus of oculomotor nerve

Also called

oculomotor nucleus · nucleus oculomotorius · nucleus of cranial nerve III

Sources: Terminologia Anatomica (TA2); Neuroanatomy, Cranial Nerve; Neuroanatomy, Brainstem; 13.2 The Central Nervous System (OpenStax (Rice University), 2022) · adapted, CC BY 4.0; Anatomía humana (4.ª ed.), tomo 1, cap. 52: Vías vestibulares.

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