Cerebellum

Question 1

Types of cerebellar deficits

Answer 1

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

Question 2

Cerebellar connections to brainstem

Answer 2

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

Question 3

Gross anatomy of cerebellum

Answer 3

• 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

Question 4

archicerebellum =

paleocerebellum =

neocerebellum

Answer 4

• 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

Question 5

Fxnl role of flocculo-nodular lobe

Answer 5

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

Question 6

Fxn of vermis/paravermal cortex

Answer 6

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

Question 7

Fxnl role of hemispheres of neocerebellum

Answer 7

• AKA “corticocerebellum”
• regions interconnected w/the cerebral cortices

Question 8

Deep nuclei of the cerebellum

Answer 8

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

Question 9

Fxn of vermal (corticonuclear) zone

Answer 9

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

Question 10

Fxn of paravermal (corticonuclear) zone

Answer 10

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

Question 11

Fxn of lateral zone of the hemispheres

Answer 11

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

Question 12

Efferent connections of vermal zone

Answer 12

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

Question 13

Defecits arising from cerebellar damage

Answer 13

• 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

Question 14

Pneumonic for cerebellar lesions

Answer 14

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

Question 15

Characteristics of cellular constituents of cerebellar cortex

Answer 15

• 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.

Question 16

Cells of the cerebellar cortex w/inhibitory actions

Answer 16

• 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

Question 17

Inputs to cerebellum carried by climbing fibers

Answer 17

• 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’).

Question 18

Role of climbing fiber input in motor learning

Answer 18

• 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