Red nucleus

At a glance

English

Red nucleus

Latin (TA2)

Nucleus ruber

System

Brain and spinal cord

Region

Head

Side

Paired, left and right

About the red nucleus

The red nucleus lies in the tegmentum of the rostral midbrain at the level of the superior colliculus, one on each side of the midline. It sits dorsomedial to the substantia nigra and ventral to the cerebral aqueduct and its surrounding grey matter. In fresh tissue it has a faint pink colour, thought to come from its rich blood supply and its high iron content, which also makes it appear dark on certain MRI sequences. Fibres of the oculomotor nerve pass through or beside it on their way to the front of the midbrain.

It has two parts. The caudal magnocellular part, made of large neurons, is well developed in many mammals but small in humans. The rostral parvocellular part, with smaller cells, makes up most of the human nucleus. The superior cerebellar peduncle, after crossing in its decussation, surrounds and enters the nucleus, bringing fibres from the interposed and dentate nuclei of the opposite cerebellar hemisphere. It also receives fibres from the motor and premotor cortex of the same side.

Output follows two routes. Most fibres from the parvocellular part descend in the central tegmental tract to the inferior olive on that side, which in turn projects to the cerebellum, closing a loop that helps adjust and learn movements. The magnocellular part gives rise to the rubrospinal tract, which crosses at once in the ventral tegmental decussation and descends in the lateral funiculus of the spinal cord just in front of the lateral corticospinal tract. In humans this tract is slight, ends mostly in the cervical cord and acts mainly on the flexors of the arm.

Since the corticospinal system dominates in primates, the red nucleus is relatively less important in humans, but it helps with coarse arm movements such as the swing of walking and with crawling in infants. Lesions in the region, as in Benedikt syndrome, combine an oculomotor palsy on the side of the lesion with tremor and poor coordination of the opposite limbs.

Function and supply

Function

Relays signals from the opposite cerebellum and the motor cortex to the inferior olive and, through the rubrospinal tract, to the cervical cord, helping coordinate coarse arm movement.

Blood supply

Paramedian branches from the posterior cerebral artery and the top of the basilar artery.