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Types of cerebellar deficits

  • all lead ==> motor function impairment
    • deficit of coordination of motor output
  • 3 main types of deficits:
  • equilibrium
  • tone
  • synergy


Cerebellar connections to brainstem

  • connected via 3 paired fiber bundles = "peduncles"
  • inferior + middle peduncles = major input 
  • superior peduncle = major output


Gross anatomy of cerebellum

  • primary fissure = separates anterior and posterior lobes
  • posterolateral fissure = defines border of the flocculo-nodular lobe
  • vermis = central longitudinal constriction
  • hemispheres = large lateral hemispheres on either side of the vermis


archicerebellum = 

paleocerebellum = 


  • archi = floccluo-nodular lobe
    • phylogenetically oldest portion of the cerebellum
  • paleo = midportion of the anterior lobe and posterior lobe = "vermis" and "paravermal cortex"
  • neo = posterior lobe
    • evolutionarily most recent


Fxnl role of flocculo-nodular lobe

  • AKA "vestibulocerebellum"
  • receives inputs from vestibular organs
  • outputs to vestibular nucleus @ brainstem


Fxn of vermis/paravermal cortex

  • AKA "paleocerebellum" AKA "spinocerebellum"
  • receives extensive input from spinal afferents 
  • outputs onto motor control nuclei


Fxnl role of hemispheres of neocerebellum

  • AKA "corticocerebellum"
  • regions interconnected w/the cerebral cortices


Deep nuclei of the cerebellum

  • 4 nuclei on each side:
  • dentate
  • interposed = globose + emboliform
  • fastigial
  • each nucleus corresponds to a corticonuclear zone


Fxn of vermal (corticonuclear) zone

  • output connections through fastigial nucleus
  • control of axial musculature, posture and balance, and integration of head and eye movements


Fxn of paravermal (corticonuclear) zone

  • connections through the interposed nuclei
  • fine-tunes movement of the limbs


Fxn of lateral zone of the hemispheres

  • connections through dentate nucleus
  • involved in higher level coordination of movements
    • including planning and initiation of movements


Efferent connections of vermal zone

  • ==> fastigial nucleus ==> vestibular nucleus and pontine reticular formation
  • some axons from flocculo-nodular lobe synapse directly @ vestibular nucleus


Defecits arising from cerebellar damage

  • Synergy, Equilibrium, and Tone.
  • Damage causes inability ipsilaterally.
  • No loss of sensation or muscle strength
  • Medial lesions impair coordination of stance and gate, axial truncal posture and  locomotion and gaze.
  • Lateral Lesions: Initiation, planning, timing, distal motor control
  • Afferent/Efferent pathways cause signs similar to cerebellar lesions

Lesions of SCP/DCN cause most severe disturbances


Pneumonic for cerebellar lesions

  • HANDS Tremor:
  • Hypotonia
  • Ataxia/Asynergia
  • Nystagmus
  • Dysarthria
  • Stance and Gait
  • Tremor (intention)


Characteristics of cellular constituents of cerebellar cortex

  • cerebellar cortex = three-layered
  • uppermost layer = "molecular layer" 
    • parallel fibers = dendrites of Purkinje cells
    • stellate cells and basket cells = scattered inhibitory interneurons
  • middle layer =  Purkinje cell layer
    • cell bodies of the Purkinje cells
  • lowest layer = granular layer
    • granule cells = small cells whose processes extend superficially to become the parallel fibers of the molecular layer.  



Cells of the cerebellar cortex w/inhibitory actions

  • stellate cells and basket cells
  • excitation of basket/stellate cells by parallel fibers ==> inhibition of neighboring Purkinje cells = "lateral inhibition"
  • inhibition of Purkinje ==> disinhibiton of deep cerebellar neurons


Inputs to cerebellum carried by climbing fibers

  • climbing fibers bring information from the contralateral inferior olive
  • CF contact as few as one dozen Purkinje cells, and each Purkinje cell is contacted (extensively) by only one climbing fiber 
    • CF-Purkinje = very powerful synaptic contact
    • single action potential in a climbing fiber gives rise to a burst of spikes in the Purkinje cell (called the 'complex spike').



Role of climbing fiber input in motor learning

  • Climbing fiber → complex spike in purkinje fibers
  • granule/parallel cells → simple spike.
  • If both inputs fire at same time, opportunity for learning / plasticity presents itself.
  • In cerebellum, coincidental firinig ==> synaptic modification = depression ==> subsequent weaker response