What is Cerebellum?

The cerebellum is a section of the brain that is most in charge of cognitive functions and motor skills.

Formation and Orientation

The cerebellum can be found at the bottom of the brain behind the pons and below that cerebral cortex under a layer of dura mater. It is also considered as a part of the “hindbrain”. The cerebellum is anatomically divided into two separate hemispheres, marked by the ‘vermis’, a small midline zone between the left and right hemispheres. But three lobes can be noted; the flocculonodar lobe, the anterior lobe and the posterior lobe.

The smallest lobe is the flocculonodar lobe (vestibulocerebellum). This lobe helps to establish balance, depth perception and field of view. It is also connected to the vestibular nuclei. In order to perform its functions, the vestibulocerebellum receives sensory information from other parts of the body.

The spinocerebellum (paleocerebellum) is made up of the medial zone of both the anterior and posterior lobes. The primary function of this area is to use information gained from the spinal cord, trigeminal nerve and sensory systems.

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The final zone is the largest, the cerebrocerebellum (neocerebellum). This is connected to the cerebral cortex, through the pontine nuclei, as well as both the ventrolateral thalamus and the red nucleus. It is said that this portion of the cerebellum is in charge of sensory evalustion, movement planning and other cognitive functions.

In the cerebellum, there are two main types of cells; granule cells and purkinje cells. Interacting with these cells are mossy fibers, climbing fibers, and parallel fibers. Both the mossy and climbing fibers enter the cerebellum from the outside, end in the deep cerebellar nuclei, and carry fiber-specific information. The parallel fibers simply create the synapses onto the dendrites of purkinje cells.

Granule cells are practically the smallest neurons and most abundant in the brain. They are found mostly in a thick layer on the bottom of the cerebellar cortex. Granule cells receive their input from mossy fibers and ultimately from pontine nuclei. They then send parallel fibers through a layer of purkinje cells.

While purkinje cells, unlike granule cells, are the largest neurons in the brain. They are found in the middle of the three layers of the cerebellum. They are surrounded by parallel fibers which connect the purkinje and granule cells through a series of synapses.

Function of the cerebellum

The theoretical functions of the cerebellum include “feedforward processing”, “divergence and convergence”, “modularity” and “plasticity”. The full function of the cerebellum is not completely known. So there are many more theories of the actual function of the cerebellum like the “learning theory” and “performing theories”.

Image Caption: Human brain with the cerebellum highlighated in purple. Credit: NIH/Wikipedia