In this note, we are going to discuss the anatomy and function of the cerebellum.
It’s a part of the brain, located within the posterior cranial fossa, and it is separated from the cerebrum by a dural septum called the tentorium cerebelli.
Function
The cerebellum helps us coordinate our movements, maintain balance and posture, and regulate muscle tone. It also plays a certain role in motor learning. Eventually, all these functions are realized by regulating the contraction and relaxation of skeletal muscles.
The cerebellum is connected to other major divisions of the brain and to the spinal cord. When we talk about connections, we actually mean nerve tracts. The nerve tracts of the cerebellum form three large structures called cerebellar peduncles. The superior cerebellar peduncle
connects the cerebellum to the midbrain,
the middle cerebellar peduncle
to the pons,
and the inferior cerebellar peduncle
to the medulla oblongata.
External features
The cerebellum consists of two cerebellar hemispheres,
connected by a so-called vermis, which literally means «worm».
On the surface of the cerebellum, we can see a large number of little folds, called cerebellar gyri or cerebellar folia.
divide the cerebellum into three structural lobes:
- Anterior
- Posterior
- Flocculonodular
The latter consists of two flocculi and one nodule, respectively.
And the horizontal fissure divides the cerebellum into two surfaces: superior and inferior.
Numerous smaller fissures divide the lobes into a large number of lobules.
There are lobules of the vermis and lobules of the hemispheres (or horizontal lobules).
Internal features
The cerebellum consists of gray and white matter, just like any other division of the central nervous system.
The white matter is represented by the neuronal processes (predominantly axons) that form the cerebellar peduncles, conduct nerve impulses, and provide connections between the cerebellum and other divisions of the brain.
The gray matter consists of the neuronal cell bodies that produce nerve impulses and form the cerebellar cortex and deep cerebellar nuclei.
There are four such nuclei:
- Dentate
- Emboliform
- Globose
- Fastigial
Collectively, the globose and emboliform nuclei are referred to as the interposed nucleus.
These nuclei can be remembered by the following mnemonic: Don’t Eat Greasy Food.
In the center of the cerebellum, we have a particular pattern of the white matter, called the «tree of life» or the «arbor vitae».
Functional areas
In addition to the anatomical (or structural) lobes and lobules, the cerebellum has three functional areas. They are formed depending on two factors. Firstly, how long ago (in evolutionary terms) a certain structure originated, and secondly, with which elements of the nervous system it has connections.
- So, the first one, the oldest part of the cerebellum, is called the archicerebellum and includes the flocculonodular lobe and fastigial nucleus. These structures are connected to vestibular nuclei of the CN VIII, so the second name of this area is the vestibulocerebellum. It plays a role in the maintenance of posture and balance.
- The newer area in evolutionary terms is called the paleocerebellum. It includes the vermis, the intermediate zone of the cerebellar hemispheres, as well as the emboliform nucleus and the globose nucleus. These structures are connected to the spinal cord, so the second name of this area is the spinocerebellum. It plays a role in the regulation of muscle tone.
Moreover, there is a particular pattern: the vermal area corresponds to the head, trunk, and proximal segments of the limbs, whereas the intermediate zone corresponds to the distal segments of the limbs. - And the last one, the newest portion, is called the neocerebellum. It includes the lateral parts of the cerebellar hemispheres and the dentate nucleus. They are connected to the cerebral cortex. Therefore, the second name of this area is the cerebrocerebellum. It plays a role in the coordination of voluntary motor activity.
Connections
We need to understand that perfectly calculated movement requires coordinated functioning of several parts of the nervous system at once. As we said, all the nerve tracts related to the cerebellum form three large structures known as cerebellar peduncles: superior, middle, and inferior.
Well, the first one, the superior cerebellar peduncle, consists of afferent and efferent connections.
The efferent tracts start off from the deep cerebellar nuclei:
- From the dentate nucleus – the dentatothalamic tract and the dentatorubrothalamic tract.
- From the interposed nucleus – the interpositorubrothalamic tract. Then all the information from the thalamus goes up to the cerebral cortex.
- And from the fastigial nucleus – the fastigiothalamic tract and the fastigiovestibular tract (or just the cerebellovestibular tract)
The afferent connections. These are mostly our mossy fibers:
- The ventral spinocerebellar tract from the lower limbs.
- The rostral spinocerebellar tract from the upper limbs.
- And the tectocerebellar tract from the superior and inferior colliculi.
The next, our middle cerebellar peduncle, consists only of afferent fibers from the pontine nuclei. The corticopontocerebellar fibers, that send down the motor plan from the cerebral cortex.
And the last one, the inferior cerebellar peduncle, consists of afferent and efferent connections.
The afferent tracts, our mossy and climbing fibers:
- The dorsal spinocerebellar tract from the Clarke nucleus.
- The cuneocerebellar tract from the upper limbs.
- The vestibulocerebellar tract from the vestibular nuclei
- The olivocerebellar tract from the inferior olive
- And the reticulocerebellar tract from the reticular formation of the brainstem
The efferent tracts:
- The cerebellovestibular tract to the vestibular nuclei
- And the cerebelloreticular tract to the reticular formation of the brainstem
Cerebellum: Anatomy & Function
- cerebellum
- cerebellum
- superior cerebellar peduncle
- pedunculus cerebellaris superior
- middle cerebellar peduncle
- pedunculus cerebellaris medius
- inferior cerebellar peduncle
- pedunculus cerebellaris inferior
- cerebellar hemispheres
- hemisphaeria cerebelli
- vermis
- vermis
- primary fissure
- fissura prima
- posterolateral fissure
- fissura posterolateralis
- anterior lobe of the cerebellum
- lobus anterior cerebelli
- posterior lobe of the cerebellum
- lobus posterior cerebelli
- flocculonodular lobe
- lobulus flocculonodularis
- horizontal fissure
- fissura horizontalis
- cerebellar cortex
- cortex cerebelli
- dentate nucleus
- nucleus dentatus
- emboliform nucleus
- nucleus emboliformis
- globular nucleus
- nucleus globosus
- fastigial nucleus
- nucleus fastigii
- interposed nucleus
- nucleus interpositus
- cerebellar folium
- folium cerebelli
- tree of life
- arbor vitae
