Cerebellum

• The cerebellar cortex is divided into three layers, with the molecular layer being the outermost.
• Purkinje cells are found only in the cerebellum and have large dendritic trees that extend throughout the granular layer.
• Climbing fibers synapse on Purkinje cell dendrites, while parallel fibers from granule cells run perpendicular to them.
• Cerebellum

  An organ of balance, located in the posterior fossa of the skull, separated from the occipital lobe by a dural fold, the tentorium cerebelli. It overlies the dorsal portion of the pons and medulla and contributes in the formation of the roof of the fourth ventricle. The cerebellum is responsible for smoothing out and refining the voluntary movements.

  
• Cerebellum

  • It is a relatively small portion of the brain -- about ten percent of the total weight, but it contains roughly half of the brain's neurons, specialized cells that transmit information via electrical signals.
• Lobes of the cerebellum

  • Anterior lobe
  • Posterior lobe
  • Flocculonodular lobe
• Layers of the cerebellar cortex

  • Molecular cell layer
  • Purkinje cell layer
  • Granule cell layer
• Deep nuclei of the cerebellum

  • Fastigial
  • Interposed (globose and emboliform)
  • Dentate nuclei
• Vermis

  Midline zone that separates the two cerebellar hemispheres

  
• Intermediate zone

  Part of each cerebellar hemisphere
• Lateral zone

  Part of each cerebellar hemisphere
• Functional subdivisions of the cerebellum

  • Vermis (paleocerebellum)
  • Lateral hemispheres (neocerebellum)
  • Flocculonodular lobe (archicerebellum)

  
• Cerebellar peduncles


  The cerebellum is connected to the brain stem by three pairs of cerebellar peduncles: superior, middle, and inferior

  
• Cerebellar peduncles


  • The superior peduncle contains primarily cerebellar efferent fibers, the middle peduncle contains primarily cerebellar afferent fibers, and the inferior peduncle contains many fibers from the medulla and spinal cord (cerebellar afferents)

  
• Functions of the cerebellum

  • Regulation and control of muscular tone
  • Control of gait
  • Coordination of movement by synergistic action, especially voluntary movement
  • Maintains equilibrium
  • Procedural (skill) learning
• Ataxia


  Defective muscular control resulting in irregular and clumsiness of movement that is not the result of muscular weakness
• Types of ataxia


  • Cerebellar ataxia
  • Vestibular ataxia
  • Sensory ataxia
• Types of cerebellar ataxia

  • Truncal ataxia due to disequilibrium
  • Limb ataxia due to incoordination
• Specific cerebellar signs


  • Intention tremor
  • Dyssynergia
  • Dysdiadochokinesia
  • Dysmetria (past pointing)
  • Impairment of the check reflex (impaired rebound)
• Non-specific cerebellar signs


  • Hypotonia
  • Scanning and staccato dysarthria
  • Ocular movement impairments (nystagmus, gaze impairment)
  • Ataxic gait
  • Pendular reflexes
• Differences between midline and cerebellar hemispheres lesions

  • Midline lesion (truncal ataxia): Broad base gait, vertical nystagmus, head and trunk titubation

  Hemispheres lesion (limb ataxia): Hypotonia, nystagmus, dysarthria, dysmetria, dyssynergia, dysdiadochokinesia, intention tremor, impaired rebound
• Causes of cerebellar ataxia

  • Sudden, acute, subacute: Metabolic, vascular, infection, inflammatory and autoimmune

  Chronic: Acquired deficit (drugs, alcoholic degeneration, MS, tumors, paraneoplastic, hypothyroidism, gluten ataxia), hereditary (posterior fossa malformations, Wilson's, ataxia-telangiectasia, spinocerebellar ataxias)