Corpus: Red nucleus

The nucleus ruber is a ganglion cell centre (nuclear area) of the extrapyramidal system in the mesencephalon. On a cross-section it can be seen macroscopically as a large, round, reddish-coloured nucleus.

The nucleus ruber gets its name from the reddish colouring in fresh cadavers, which is caused by the high iron content in the perikarya and its good blood supply.

The nucleus ruber is a round nucleus in the mesencephalon. It lies between the periaqueductal grey and the substantia nigra. It is surrounded posteriorly by the reticular formation. Together with the nucleus olivaris inferior and the nucleus dentatus, it forms the corner points of the Guillain-Mollaret triangle.

The nucleus ruber is subdivided into:

• Pars magnocellularis: It consists of large cells and forms the older part in terms of developmental history.
• Pars parvocellularis: It consists of small cells and forms the larger part of the nucleus.

The nucleus ruber is an important control centre in the motor system. It projects its efferents into the spinal cord and thus occupies an important position within the extrapyramidal motor system (EPMS). It influences muscle tone and posture.

The nucleus ruber receives impulses from:

• motor cortex via tractus corticorubralis
• cerebellum via the cerebellorubral tract
• superior colliculi
• precentral gyrus
• Pallidum
• Thalamus
• Nuclei vestibulares

The nucleus ruber emits efferents to:

• the spinal cord via tractus rubrospinalis
• the nucleus olivaris inferior via tractus tegmentalis centralis
• the mesencephalic tectum via the rubrotectal tract and
• the ventral anterolateral nucleus of the thalamus via the rubrothalamic tract

A lesion of the nucleus ruber causes an intention tremor and a reduction in muscle tone on the contralateral side. Choreatic-athetotic movements may also occur. Damage to the ruberous nucleus often leads to loss of the ipsilateral oculomotor nerve (nerve III) and consequently to double vision, as some of the fibres of the nerve pass through the ruberous nucleus before exiting.

See also: Benedict's syndrome