CEREBELLUM This course outline is designed to provide you with a study guide. Use the lecture, book, and other resources to expand on its contents.

Lesson Objectives

1. Explain the basic function of the cerebellum and describe how it accomplishes this function.

2. Explain how cerebellar functions interconnect with the motor system.

3. Describe the effects of cerebellar damage.

General Information

• Size has increased with phylogeny--with need for control in skilled responses
• Functions as a correlation center with sensory and motor outflow
• Stimulation--no conscious sensation nor overt movements
• Correlates the muscle-tendon--vestibular message, as well as tactile, visual and auditory; computes most effective muscle effort required, then relays to:
  • Motor cortex (via ventral thalamic nucleus)
  • Motor-neuron pool

Functions

Damage produces dysmetria and asynergia

• Dysmetria--results from loss of proprioceptive input

• Asynergia--motor deficit--loss of involuntary motor responses
  • Injury to internal nuclei--more severe effects
  • Injury to efferent tracts--most severe effects

• Diagnosis of cerebellar injury is good but treatment is not employed

Cerebellar Peduncles

Superior cerebellar peduncle

• Afferent: Ventral cerebellar path
• Efferents:
  • Fastigo-bulbar--to inferior cerebellar peduncle
  • Brachium conjunctivium--to red nucleus from dentate; motor cortex via thalamus

Middle cerebellar peduncle

• Afferent only: Crossed fibers from pontine nucleus relay cortical and extrapyramidal information to brachium pontis.

Inferior cerebellar peduncle

• Afferents
  • Vestibulo-cerebellar path (juxarestiform)
  • Dorsal spinocerebellar path (restiform)
  • Olivary nucleus: ventral internal arcuate fibers to restiform body

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Cerebellar Cortex

Nuclei

• Dentate
• Fastigial
• Globose
• Emboliform

• Afferent fibers (mossy fibers) synapse in granular layer on dendrites of granule cells
• Granule cells project to outermost (molecular layer) and branch in parallel with felia
• Granule cell axons synapse with many Purkinje cells whose dendritic fields are at right angles with the granule cells
  • Cell bodies of Purkinje cells form a second layer of cerebellum
  • Collaterals from Purkinje cells (climbing fibers) return to molecular layer and synapse with other Purkinje cell dendrites
  • Basket cells
• All Purkinje axons synapse with cell bodies in cerebellar nuclei

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Formal divisions

1. Archicerebellum--prefish & fish (smallest)
   • Flocculi -- vestibular correlation center
   • Nodule
   • Connections:
     • Vestibular to juxtarestiform body;
     • Fastigial nuclei to fastibulobulbar tract to vestibular nucleus and Reticular formation.
   • Lesions lead to vestibular symptoms

2. Paleocerebellum (intermediate in size)
   • Anterior lobe: connects spinocerebellar tract
   • Dominant system in quadrupeds
   • Receives olivary and cerebropontine connect

3. Neocerebellum--develops w/ skilled movements
   • Middle lobes--largest
   • Olivary and cerebral control only
   • Olivary nucleus: relays extrapyramidal system

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Afferents and Efferents

Afferents

1. Vestibulo-cerebellar path
   • 8th--juxtarestiform body--posterior lobe

2. Spinocerebellar paths (few cross)
   • Ventral spinocerebellar tract (older path)
   • Dorsal spinocerebellar tract
     • Synapse at Nucleus Dorsalis of Clarke; enters restiform body

3. Olivocerebellar tract--relays both spinal and extrapyramidal contributions
   • Olivary nucleus - cross as ventral internal arcuate fibers and enter restiform body; mainly to middle lobe

4. Cortico-pontocerebellar tract
   • Arises from motor areas (not projection)
   • Corona radiata

Efferents

• Fastiobular--from fastigial nucleus
• Brachium conjunctivium--from dentate nucleus to red nucleus, thalamus, globus pallidus
• Motor neuron pool via rubrospinal and reticulospinal tracts
• Others influence motor systems at cortical level via thalamus and in basal ganglia

Terms to Know