Cerebellum is a part of the brain that coordinates movement, posture and balance. It lies in the posterior cranial fossa, the compartment at the back of the skull base, behind the brain stem and below the back of the cerebrum, the large upper part of the brain.
Where is the cerebellum located?
The cerebellum occupies much of the posterior cranial fossa. In front of it are the pons and medulla, parts of the brain stem that connect higher brain regions with the spinal cord. Behind and below it is the occipital bone, which forms the back and part of the base of the skull.
The tentorium cerebelli separates the cerebellum from the occipital lobes, the posterior regions of the cerebrum. This tentorium is a fold of dura mater, the tough outer membrane covering the brain. The fourth ventricle, a cavity containing cerebrospinal fluid, lies between the cerebellum and the pons and upper medulla; cerebrospinal fluid surrounds and cushions the brain and spinal cord.
On the lower surface, the tonsil of cerebellum is a rounded lobule, or small anatomical subdivision. The paired tonsils lie near the foramen magnum, the large opening through which the brain stem continues into the spinal cord.
What are the main parts and surfaces of the cerebellum?
The left hemisphere of cerebellum and right hemisphere of cerebellum are its lateral portions. They are joined centrally by the vermis, a narrow midline region. The upper surface is broadly convex, while the lower surface has a central depression between the hemispheres.
Narrow, leaf-like folds called folia cover the surface. Grooves between these folds are called fissures; the deeper fissures separate larger subdivisions. The primary fissure separates the anterior and posterior lobes, while the posterolateral fissure separates the posterior and flocculonodular lobes.
| Lobe | Anatomical position | Main functional association |
|---|---|---|
| Anterior lobe | Above and in front of the primary fissure | Posture and coordination of trunk and limb movement |
| Posterior lobe | Between the primary and posterolateral fissures | Planning and coordination of skilled movement |
| Flocculonodular lobe | On the lower surface, comprising the flocculi and nodule | Balance and control of eye movements |
The flocculus is a small lateral component of the flocculonodular lobe; its central component is the nodule of vermis. On the upper vermis, the culmen lies in the anterior lobe and the declive lies in the posterior lobe. Anatomical lobes and functional regions overlap, but their boundaries are not identical.
What is inside the cerebellum?
The cerebellar cortex is the outer layer of grey matter, tissue containing nerve-cell bodies and their local connections. Beneath it lies white matter, formed mainly by nerve fibres carrying signals between regions. In a midline section, the branching white matter has a tree-like appearance called the arbor vitae.
The cortex has molecular, Purkinje cell and granular layers. The molecular layer contains many nerve-cell branches; the Purkinje cell layer contains the large cells that provide the cortex's output. The granular layer contains numerous small nerve cells called granule cells.
Deep within the white matter are the dentate, emboliform, globose and fastigial nuclei. A nucleus is a group of nerve-cell bodies within the central nervous system, meaning the brain and spinal cord. These deep nuclei provide most cerebellar output, although some cortical output passes directly to brain-stem centres involved in balance.
How does the cerebellum connect to the rest of the nervous system?
Cerebellar peduncles are bundles of nerve fibres connecting the cerebellum to the brain stem. They carry incoming information and outgoing signals, rather than acting as peripheral nerves supplying an organ.
- The superior cerebellar peduncle connects with the midbrain, the upper part of the brain stem, and carries mainly outgoing signals.
- The middle cerebellar peduncle connects with the pons and carries incoming information relayed from the cerebral cortex, the outer grey matter of the cerebrum.
- The inferior cerebellar peduncle connects with the medulla and carries information from the spinal cord and brain stem, as well as some outgoing signals.
Incoming information includes proprioception, the sense of body position and movement, and vestibular information about head position and motion from the inner ear. These connections allow the cerebellum to compare intended movements with ongoing movement.
What supplies blood to the cerebellum?
The superior cerebellar artery usually arises from the basilar artery and supplies much of the upper surface. The anterior inferior cerebellar artery also usually arises from the basilar artery and supplies the front and lower lateral region.
The posterior inferior cerebellar artery usually arises from the vertebral artery and supplies much of the lower posterior surface. These territories overlap and vary between individuals. The vertebral arteries unite to form the basilar artery in front of the brain stem.
The superior cerebellar veins and inferior cerebellar veins drain blood towards the dural venous sinuses, blood-filled channels within the dura mater.
What does the cerebellum do?
The cerebellum adjusts the timing, force and sequence of muscle activity. It helps movements remain coordinated rather than initiating voluntary movement itself. It also contributes to motor learning, the refinement of movements through practice.
Its central regions contribute particularly to posture and movements of the trunk and nearby limb segments. More lateral regions contribute to planning and coordinating skilled limb movements. Connections with the inner-ear balance system help maintain equilibrium and coordinate eye movements with head movement.
How can you locate the cerebellum in the 3D model?
In the 3D model next to this article, rotate towards the back of the head and hide or fade overlying structures to locate the cerebellum below the cerebrum. Select and isolate it to examine its outline, then rotate between upper and lower views. A sagittal section, a cut dividing left and right portions, provides an orientation for considering its midline relationship to the brain stem.