Cerebellum

Abstract

The cerebellum is a 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) that lie in the inner white matter. The cerebellar nuclei send efferent impulses via three cerebellar peduncles to the thalamus, red nucleus, and reticular formation to execute cerebellar functions.

Overview

  • Structure
    • The cerebellum is composed of 2 hemispheres separated by a midline vermis.
      • The most caudal section of the cerebellar hemispheres is referred to as cerebellar tonsils.
    • Three peduncles connect the cerebellum to the brain stem
    • The cerebellum is comprised of: :
      • Grey matter in the outer cortex: receives afferent inputs from the cerebrum and the spinal cord and transmits them to the cerebellar nuclei
      • White matter in the inner cortex
        • Arranged in a branching tree-like pattern
        • Contains the four deep cerebellar nuclei
  • Location
  • Function
    • Coordination of motor movements
    • Motor planning and balance
    • Muscle tone control

Cerebellar tonsil herniation through the foramen magnum due to a local mass or increase in intracranial pressure can cause life-threatening compression of the brainstem and may result in cardiopulmonary arrest.

Gross anatomy

Anatomical subdivisions

Functional subdivisions

Three functional zones Input Function

Effect of lesions

(see also “Clinical features” in cerebellar syndromes)

Cerebrocerebellum

(Lateral hemispheres)

  • Compares cerebral motor output with proprioception at the site where the motor movement is about to occur
  • Plans movements that are about to occur
  • Coordinates 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
  • Coordinates ongoing motor execution
    • Vermis: coordinates movements of the central body (i.e., trunk, head, and proximal limbs)
    • Intermediate zones: coordinate movements of distal limbs (hands, fingers, feet, toes)
  • Helps maintain 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


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

Cerebellar peduncles

The cerebellum has three pairs of peduncles through which afferent and efferent fibers travel to and from the ipsilateral cerebellum.

Characteristics Mainly carries
Superior cerebellar peduncles (SCP)
  • Connects the cerebellum to the midbrain
  • Major output 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
  • Afferent tracts from the contralateral cortex
Inferior cerebellar peduncles (ICP)
  • Connects the cerebellum to the medulla and spinal cord
  • Major input pathway
  • Afferent tracts from spinal cord with ipsilateral proprioceptive information


Cerebellar tracts

Afferent tracts (input)

Afferent tracts arise from three main sources and travel mainly through the inferior (ICP) and middle (MCP) cerebellar peduncles

Source Afferent tracts Course Function
Cerebral cortex Corticopontocerebellar tract Cerebral cortexcorona radiatainternal capsulepontine nucleimossy fibers → cerebellar hemisphere via MCP Carries information for motor planning, motor learning, and cognition
Cortico-olivocerebellar tract Cerebral cortexcorona radiatainternal capsuleinferior olivary nucleiclimbing fibers → cerebellar hemisphere via ICP
Corticoreticulocerebellar tract Cerebral cortexcorona radiatareticular formation in pons and medulla → mossy fibers → cerebellar hemisphere via the ICP and MCP
Spinal cord Spinocerebellar tract Posterior horn of the spinal cord → mossy fibers → cerebellar hemisphere via the ICP and SCP Carries ipsilateral proprioceptive information
Vestibular nerve Vestibulocerebellar tract Vestibular nerve → vestibular nucleimossy fibersipsilateral flocculonodular lobe via the ICP Carries information of the vestibular organ

The spinocerebellar tract carries proprioceptive info from Golgi tendon organs and muscle spindles to the ipsilateral cerebellum through the inferior cerebellar peduncle. The information about joint and body position is used to keep balance and to coordinate and modulate movements.

Cerebellar nuclei and efferent tracts (output)

Originate from the four deep cerebellar nuclei and travel mainly via the SCP, except for tracts from the fastigial nucleus, which travel via the ICP

Tract Cerebellar nuclei Main characteristics Origin Efferent tract Peduncle Function
Rubrospinal tract Dentate nucleus
  • Lateral hemispheres
  • SCP
  • Control ipsilateral motor coordination

Emboliform nucleus and globose nucleus

  • Function together, and are known as the interposed nucleus
  • Intermediate cerebellar zones
  • SCP
  • Tone of ipsilateral muscles
Cerebellovestibular tract Fastigial nucleus
  • Most medial nucleus
  • Vestibular complex
  • Reticular formation
  • Fastigial nucleus → ICP → bilateral vestibular nuclei → vestibulospinal tract
  • Fastigial nucleus → ICP → bilateral reticular formation → reticulospinal tract → motor neurons from spinal cord
  • ICP
  • Coordination of balance and saccadic ocular movements
  • Influences stretch reflex and motor movements

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

Vasculature

Microscopic anatomy

  • The cerebellar cortex is composed of 5 types of neuronal cells, densely packed and arranged in 3 layers.
  • All cerebellar neurons, except for the granule cells, are GABAergic inhibitory neurons.
Layer Cell types Connectivity

Molecular layer

(Outermost layer)

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

Purkinje 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
  • Purkinje fibers are the only efferent pathway to the deep cerebellar nuclei.

Granular layer of the cerebellum

(Inner layer)

  • Golgi cells: located in the upper portion of the granular layer
  • Granule cells
    • Most abundant cell type in the brain
    • Composed of small, densely packed neurons

The input pathway to the cerebellar cortex includes mossy fibers and climbing fibers. The deep nuclei are the only output from the cerebellum.

Inhibitory GABA is the neurotransmitter of all cerebellar cells except granule cells, whose neurotransmitter is the excitatory glutamate!

Embryology

The cerebellum derives from the hindbrain and the metencephalon.

For more information on the embryology of the nervous system see rhombencephalon, neurulation, and spinal cord tracts and reflexes.

Clinical significance

last updated 08/21/2018
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