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• Cerebellum


  • Located below tentorium cerebelli within posterior cranial fossa
  • Formed of 2 hemispheres connected by the vermis in midline
  • Gray matter is external
  • White matter is internal, contain several deep nuclei with the largest is the dentate nucleus

  
• Cerebellum


  • Maintenance of posture and balance
  • Maintains muscle tone
  • Coordinates voluntary motor action
• Two main fissures of the cerebellum


  • The primary fissure separates the posterior lobe from the anterior lobe
  • The posterolateral fissure (uvulonodular fissures) separates the flocculonodular lobe from the posterior lobe

  
• Three lobes of the cerebellum

  • Anterior lobe
  • Posterior lobe
  • Flocculonodular lobe

  
• Anatomical divisions of the cerebellum


  • Vermis
  • Intermediate zone
  • Lateral hemispheres

  
• Vermis


  Influences the movements of the long axis of the body (neck, shoulders, thorax, abdomen and hips)
• Intermediate zone


  Controls muscles of the distal parts of the limbs (hand and feet)
• Lateral zone


  Concerned with planning of sequential movements of the entire body
• Structure of cerebellar cortex


  • Molecular layer
  • Purkinje cell layer
  • Granular layer

  
• Molecular layer


  Consists of axons of granule cells (parallel fibers) and dendrites of Purkinje cells
• Purkinje cell layer


  Contains large neuronal cell bodies (Purkinje cells) which are flask shaped
• Granular layer


  Contains small neurons called granular cells and Golgi cells (inhibitory)
• Cerebellar cortical mechanisms


  • Climbing fibers: terminal fibers of the olivocerebellar tracts
  • Mossy fibers: terminal fibers of all other cerebellar afferent tracts

  
• Climbing fibers and mossy fibers are excitatory to Purkinje cells
• Purkinje Cells


  The only output neuron from the cortex, utilizes GABA to inhibit neurons in deep cerebellar nuclei
• Granule Cells


  Intrinsic cells of cerebellar cortex, use glutamate as an excitatory transmitter, excite Purkinje cells via axonal branches called "parallel fibers"
• Basket Cells and Stellate Cells


  Inhibitory interneurons, utilize GABA to inhibit Purkinje cells
• Functional anatomy of the cerebellum

  • Spinocerebellum
  • Cerebrocerebellum
  • Vestibulocerebellum
• Spinocerebellum

  Most of the vermis of the posterior and anterior cerebellum plus the adjacent intermediate zones on both sides of the vermis, projects through fastigial and interposed nuclei, has a somatotropic organization, receives major inputs from the spinocerebellar tracts, involved in the integration of sensory input with motor commands to produce adaptive motor coordination, controls posture and movement of trunk and limbs

  
• Cerebrocerebellum


  Located in the lateral hemisphere, participates in the planning of movement, projects to the dentate nucleus, receives afferent input from the entire contralateral cerebral cortex and projects via the thalamus to the primary motor cortex and premotor cortex plus prefrontal cortex

  
• Vestibulocerebellum


  Located in the flocculonodular lobe, functions in maintaining balance and controlling head and eye movements, projects to vestibular nuclei, involved in vestibular reflexes and postural maintenance

  
• Cerebellar afferent fibers


  • From cerebral cortex: Corticopontocerebellar pathway, Cerebro-olivocerebellar pathway, Cerebroreticulocerebellar pathway
  • From spinal cord: Anterior spinocerebellar tract, Posterior spinocerebellar tract, Cuneocerebellar tract
  • From vestibular nerve
  • Other afferents: Red nucleus, Tectum

  
• Cuneocerebellar tract


  Originates in nucleus cuneatus of medulla oblongata, enters the inferior cerebellar peduncle ipsilaterally, receives proprioception (muscle-joint sensations) from the upper limb and upper part of thorax

  
• Cerebellar efferent fibers


  • Dentothalamic pathway
  • Globose-emboliform-rubral pathway
  • Fastigial vestibular pathway
  • Fastigial reticular pathway

  
• Inferior cerebellar peduncle


  Primarily contains afferent fibers from the medulla, as well as efferents to the vestibular nuclei

  
• Middle cerebellar peduncle


  Primarily contains afferents from the pontine nuclei

  
• Superior cerebellar peduncle


  Primarily contains efferent fibers from the cerebellar nuclei, as well as some afferents from the spinocerebellar tract

  
• Signs and symptoms of cerebellar disease


  • Hypotonia: decrease in muscle tone
  • Dysmetria (past pointing): movements ordinarily overshoot their intended mark
  • Ataxia (inaccuracy and disturbances of voluntary movement)
  • Tremors: involuntary oscillations of limbs ("intention tremor")
  • Postural changes and alteration of gait (wide-based gait) to compensate for loss of muscle tone
  • Failure of Progression
  • Dysdiadochokinesia (difficulty performing rapid alternating movements)
  • Dysarthria: Disorders of speech
  • Nystagmus: rhythmic oscillations of the eyes