Cerebellum

The cerebellum (maskaxda-yar in Somali) is part of the central nervous system. It is located at the lower back of the head, beneath the cerebrum and connected to the brainstem.

The primary function of the cerebellum is motor coordination. It refines the precision, timing, and smoothness of movements initiated by commands from the brain. It is therefore often described as the 'quality control' centre, comparing motor commands sent from the brain with feedback received from the body.

Structure

The cerebellum has two lateral hemispheres and a central region called the vermis. Its outer surface is covered by a highly folded cortex, which creates a large surface area in a small space. The interior contains white matter fibres and deep nuclei, which relay output to other brain regions.

The cerebellar cortex has a uniform structure throughout. The largest neurons are Purkinje cells, which have extensive branching and are the only output pathway from the cortex. Two types of fibres project into it: mossy fibres and climbing fibres.

Function and learning

The cerebellum plays a role in motor learning. When a person learns a skill such as cycling or writing, changes in neural connections make the movement smooth and requiring less conscious attention. Modern research has also shown involvement in cognitive and language functions, though the extent of this role remains debated.

Damage

Cerebellar damage can cause ataxia—uncoordinated movement, unsteady gait, tremor when reaching for an object, and irregular speech. Causes include stroke, head injury, alcohol intoxication, genetic disorders, and tumours. Damage typically appears on the same side of the body as the lesion.