Cerebellum

Summary

The cerebellum is the part of the hindbrain that lies within the posterior cranial fossa, inferior to the occipital lobes and dorsal to the brainstem. It consists of three lobes (the anterior, posterior, and flocculonodular lobe). Functionally, it is divided into three zones. These are the cerebrocerebellum (the lateral zones), which receives sensory information from the cerebral cortex and is responsible for the planning of movements that are just about to occur (motor planning); the spinocerebellum (the vermis and intermediate zones), which receives proprioceptive information from the dorsal columns of the spinal cord and is responsible for the coordination of movements (motor execution); and the vestibulocerebellum (the flocculonodular lobe), which receives information from the vestibular nuclei and visual cortex and is responsible for balance and ocular movements. The cerebellar cortex transmits the information received from the three afferents (i.e., the cerebrum, spinal cord, and vestibular nuclei) to the four cerebellar nuclei (dentate, emboliform, globose, and fastigial) within the inner white matter. The cerebellar nuclei send efferent impulses to the thalamus, red nucleus, and reticular formation to execute cerebellar functions. The cerebellar tracts travel through the cerebellar peduncles.

Gross anatomy

Overview

  • Location
  • Function
    • Control of balance and ocular movements
    • Planning of movements that are about to occur
    • Coordination of complex and sequential movements
    • Maintenance of muscle tone

Structure [1]

  • The cerebellum has 2 hemispheres separated in the midline by the cerebellar vermis.
  • The cerebellar tonsil is an ovoid lobule located on the inferomedial aspect of each cerebral hemisphere, above the foramen magnum
  • Sulci and fissures further divide the cerebellum into lobes (see “Lobes and fissures” below)

Cerebellar tonsil herniation through the foramen magnum can occur due to a Chiari malformation or an increase in intracranial pressure, resulting in brainstem compression and cardiopulmonary arrest.

Lobes and fissures

Cerebellar peduncles

  • Three pairs of cerebellar peduncles connect the cerebellum to the brain stem.
  • Afferent and efferent cerebellar tracts travel through the peduncles to and from the ipsilateral cerebellar cortex.
Peduncle Characteristics Tracts
Superior cerebellar peduncles (SCP)
  • Connects the cerebellum to the midbrain
  • Major efferent pathway
  • Efferent tracts from the deep nuclei of the cerebellum to the contralateral cortex
Middle cerebellar peduncles (MCP)
  • Connects the cerebellum to the pons
  • Largest peduncle
  • Major afferent pathway
  • Afferent tracts from the contralateral cortex (pontocerebellar mossy fiber pathway)
Inferior cerebellar peduncles (ICP)
  • Connects the cerebellum to the medulla and spinal cord
  • Afferent and efferent pathways
  • Afferent tracts carrying ipsilateral proprioceptive information from the spinal cord
  • Efferent tract composed primarily of Purkinje cell axons


Cerebellar lesions cause neurological deficits on the ipsilateral side!

Vasculature [1]


References:[2][3][4][5]

Functional zones of the cerebellum

Input Function

Effect of lesions

Cerebrocerebellum

(lateral hemispheres)

  • Planning and execution of movements
  • Coordination of complex and sequential motor movements
  • Nonmotor functions: cognition, language, learning, and emotions
  • Abnormal coordination of ipsilateral voluntary movements ,
    • Fall towards the side of the lesion (ipsilateral)
    • Dysdiadochokinesis
    • Dysmetria
    • Intention tremor
  • Scanning speech (ataxic dysarthria)

Spinocerebellum

(vermis and intermediate zones)

  • Spinal cord
    • Vermis: input from the trunk and proximal portions of the limbs
    • Intermediate zones: distal portion of the limbs
  • Coordination of body and limb movement
    • Vermis: central body (trunk, head, and proximal limbs)
    • Intermediate zones: distal limbs (hands, fingers, feet, toes)
  • Maintenance of muscular tone
  • Vermis: trunk and proximal limb muscles affected
  • Intermediate zones: ipsilateral distal limb muscles affected

Vestibulocerebellum

(flocculonodular lobe)

  • Balance
  • Ocular movements and gaze stability
  • Vertigo
  • Nystagmus

For further information on the effects of cerebellar lesions, see “Clinical features” in cerebellar syndromes.

Lesions of the lateral hemispheres result in ipsilateral ataxia. Lesions of the vermis result in truncal ataxia. Lesions of the flocculonodular lobe result in nystagmus.

References:[6][7]

Microscopic anatomy

The cerebellum is composed of the outer gray matter (cerebellar cortex) and inner white matter (cerebellar medulla).

Cerebellar cortex [7]

  • Receives afferent inputs from the cerebrum, spinal cord, and vestibular nuclei
  • Sends neural impulses to the cerebellar nuclei
  • Composed of 5 types of neuronal cells, densely packed and arranged in 3 layers
  • The cortex is primarily an inhibitory structure; all cerebellar cells except granule cells are inhibitory.
Layer Cell types Function

Molecular layer

(outermost layer)

  • Receives excitatory input from parallel fibers
  • Sends inhibitory impulses to Purkinje cells

Purkinje cell layer

(middle layer or ganglionic layer)

  • Receive excitatory input from climbing fibers and granule cells
  • Send inhibitory impulses to the deep cerebellar nuclei and thereby control the output of all motor coordination of the cerebellum

Granular layer of the cerebellum

(inner layer)

Cerebellar medulla

Glutamate is the neurotransmitter of granule cells, which are the only excitatory cerebellar cells. GABA is the inhibitory neurotransmitter of all other cerebellar cells.

Purkinje cells provide the only efferent effect from the cerebellar cortex to the cerebellar nuclei, and, thus, play an essential role in the regulation of cerebellar output!

References:[6][8][9][7][10][11]

Cerebellar tracts

Afferent cerebellar tracts (input) [6][2]

Afferent cerebellar tracts
Source Tracts Course Function
Cerebral cortex
  • Motor planning, motor learning, and cognition

Spinal cord

  • Ipsilateral proprioceptive information

Vestibular nerve



Excitatory input to the cerebellar cortex travels through mossy fibers and climbing fibers!

Mossy fibers terminate on granule cells. Climbing fibers terminate on Purkinje cells.

Efferent tracts (output) [2]

Tract Nucleus Course Function
Rubrospinal tract
  • Ipsilateral motor coordination
  • Tone of ipsilateral skeletal muscles
Cerebellovestibular tract
  • Coordination of balance and saccadic ocular movements
  • Stretch reflex and motor movements

Deep cerebellar nuclei (from lateral to medial): "Don't Eat Greasy Food" (Dentate, Emboliform, Globose, Fastigial).

The deep nuclei are the only output from the cerebellum.

References:[12][3][5][13][14][15][16][17][18][19]

Embryology

The cerebellum derives from the hindbrain (rhombencephalon) and metencephalon.

For more information on the embryology of the nervous system, see “Embryology” in the cerebral cortex, basal ganglia, and meninges.

Clinical significance