Cerebellum Anatomy and Overview

Study Notes

The cerebellum is located below the tentorium cerebelli within the posterior cranial fossa
It is formed of two hemispheres which are connected by the vermis
The gray matter is external, and white matter is internal, containing several deep nuclei, with the largest being the dentate nucleus

Divided into three prominent anatomical lobes — anterior lobe, posterior lobe, and flocculonodular lobe
Further divisions include: vermal zone, intermediate (paravermal) zone, and lateral zone
The cerebellum is attached to the brain stem by three pairs of tracts called cerebellar peduncles
- Inferior cerebellar peduncle – afferents (input) from spinocerebellars (posterior), cuneocerebellars, vestibulocerebellars, and olivocerebellars
- Middle cerebellar peduncle – afferent, primarily pontocerebellars
- Superior cerebellar peduncle –primarily efferent (output) to cerebellorubrals (to red nucleus) and cerebellothalamics (to VL nucleus of thalamus)
The cerebellar nuclei comprise four paired deep gray matter nuclei:
- Dentate nuclei (largest and most lateral)
- Emboliform nuclei
- Globose nuclei
- Fastigial nuclei (most medial)

Contains three layers: molecular, Purkinje cell, and granular layers.
- Molecular layer: inhibitory interneurons (GABA-ergic) - Stellate cells and basket cells
- Purkinje cell layer: neuron cell bodies
- Granular layer: granule cell axons form parallel fibers

Input is primarily via climbing fibers (from olivocerebellar tracts) and mossy fibers (from other cerebellar afferent tracts).
Both are excitatory to Purkinje cells. A single Purkinje neuron makes synaptic contact with only one climbing fiber.
A single mossy fiber may stimulate thousands of Purkinje cells through granule cells
Granule cells receive input from mossy fibers and project to the Purkinje cells

Vestibulocerebellum: flocculonodular lobe, balance, eye movements and vestibular reflexes
- Inputs: vestibular nerve and nuclei
- Outputs: vestibular nuclei
Spinocerebellum (paleocerebellum): vermis and intermediate hemisphere of the cerebellar cortex, fastigial and interposed nuclei
- Has somatotropic organization
- Receives input from spinocerebellar tracts.
- Outputs: rubrospinal, vestibulospinal, and reticulospinal tracts, controlling posture and movement
Cerebrocerebellum (neocerebellum): lateral hemispheres, dentate nuclei
- Extensive connections with cerebral cortex via pontine nuclei, VL thalamus
- Involved in planning, timing, and coordination of movements; entire contralateral cerebral cortex is afferent input
- Output:thalamus

From brain and brainstem centers (cerebral cortex, red nucleus, vestibular nuclei, reticular formation, and inferior olivary nucleus) to form a “plan” for movement
From peripheral receptors:
- Dorsal spinocerebellar tract: muscle spindles, Golgi tendon organs, joint and pressure receptors; primarily ipsilateral, and vermis + paravermal intermediate zone
  - Fine movements
- Ventral spinocerebellar tract: quickly returns to the spinocerebellum copies of the motor commands in the same direction; primarily ipsilateral, and vermis + paravermal intermediate zone
  - Gross movements

From Vermis: fastigial nucleus → vestibular nuclei and RF of the brain stem (axial muscles)
From intermediate zone: interposed nucleus → contralateral thalamus, red nucleus, and RF of the brain stem (distal extremities)

Regulation of Equilibrium: vestibular receptors, sensory signals to the vestibulocerebellum, adjustment of axial and proximal limb muscles, superior colliculus→ coordination with head movements, maintaining clear vision
Regulation of Posture: vermis→ sensory info from muscle spindles and joint proprioceptors to adjust the tone and contraction of axial and proximal limb muscles
Coordination of Voluntary Movement: proper sequence to smoothly execute movements
- Comparator and Error-Correction mechanisms involve the intermediate zone of the spinocerebellum