The cerebellum is a part of the brain located at the back of the head, below the temporal and occipital lobes, and above the brain stem. Similar to the cerebrum, the cerebellum has two hemispheres, connected by the vermis. It is fern-shaped and, like the brain, it has many gyri and sulci.
💡 Did you know? Cerebellum means "little brain" in Latin.
📔 Vermis: rounded and elongated central part of the cerebellum, between the two hemispheres.
Parts of the Cerebellum
💡 Did you know? The human cerebellum is only about 10% of our brain in terms of volume. However, it holds about half of all the neurons in our entire body.
Grey matter: constitutes the cerebellar cortex, which is made up of many neurons and their fibers laid out in three layers: the outer molecular layer, the middle layer of Purkinje cells, and the inner granular layer:
Layer 1: Outer molecular layer. The most superficial layer and relatively thick.
Layer 2: Middle layer of Purkinje. Bodies of Purkinje cells laid out in a single row with glial cells in between. Their dendrites are in the molecular layer, while their axons go towards the granular layer and to the white matter.
Layer 3: Inner granular layer: very small cells.
White matter: contains some nuclei.
Cerebellar peduncle: union between the cerebellum and the brain stem (superior: fibers to/from mesencephalon; medial: fibers to/from metencephalon/pons; inferior: fibers to/from brain stem).
Deep cerebellar nuclei: Dentate, emboliform, fastigial, and globose. The nuclei receive GABAergic (inhibitory) input from the Purkinje cells, as well as excitatory input from the mossy and climbing fibers.
Cerebellar lobes: anterior lobe, posterior lobe, and flocculonodular lobe.
Functions of the Cerebellum
The cerebellum coordinates voluntary muscle movements and maintains posture, balance, and equilibrium.
Archicerebellum (the oldest part of the cerebellum; flocculonodular lobe + fastigial nuclei): concerned with equilibrium, and ocular movement, and is connected with the inner ear.
Paleocerebellum (vermis + globose/emboliform nuclei): muscle tone, posture, and crude movements of the limbs.
Neocerebellum (cerebellar hemispheres + dentate nuclei): coordinates skilled movements initiated at cortical levels. Strength, trajectory, speed, and mental movement planning.