•The Cerebellum

•Anatomy of the Cerebellum

• 2 hemispheres with vermis in between

• Very folded cerebellar cortex

• Underlying white matter & deep nuclei

• Deep nuclei are the output pathway

• Massive cerebellar peduncles (axon bundles to and from cerebellum) connecting to brainstem

Primitive Cerebellum in Blue

•Evolution of Cerebellum

• Oldest part is the flocculonodular lobe - it gets input from the vestibular system (Vestibulocerebellar path)

• Next: the region around the vermis gets proprioceptive & cutaneous input via spinal cord (spinocerebellar tr.)

• Most recent region – the hemispheres- get input from cortex via the pons (corticopontocerebellar path)

• All input goes to cerebellar cortex; all output is from the deep cerebellar nuclei

• Loop-like feedback to each of those sources of input

Mode of Functioning

• Totally unconscious

• Computer-like feedback loops

• Moment-to-moment adjustments

• Ipsilateral in its control (right side of cerebellum related to movements of right side of body)

•Cerebellum Is Needed For:

• Fluid coordination of movements

• Synergy/cooperation between muscles

• Precise timing & targeting of movements

• Appropriate force & muscle tone

• Cerebellum is storing these details during motor learning

• Automatic adjustments to changing conditions & to maintain balance

•Symptoms of Cerebellar Damage

• Asynergia - loss of fluid coordination & cooperation between muscles; movements jerky & disjointed

• Dysmetria - poor targeting of movement; over- or under-reach

• Can’t do finger to nose test

• Intention tremor while targeting movements (see clip)

• Dysarthria/Dysphonia - slurred, uncoordinated speech & speech volume

• Lateral lesion- affects ipsilateral limbs

Symptoms of Cerebellar Damage

• Disturbed balance (can’t balance on 1 foot; walk heel-to-toe)

• Gait ataxia – wide-based, staggering walk, may shuffle,veer to side, may fall

• Poor muscle tone (hypotonia)

• Adiadochokinesia/Dysdiadochokinesia - can’t rapidly alternate movements http://www.neuroexam.com/36.html

• Nystagmus-jerky, oscillating eye movements (see dbnystag. clip)

• Midline lesion most likely to cause gait, posture, balance problems - Romberg test http://www.neuroexam.com/37.html

•Test for Dysdiadochokinesia

•Medulloblastoma

• A cerebellar tumor usually originating in the vermis, which then presses down on the brainstem

• Accounts for ~1 in 20 brain tumors (1 in 5 in kids). 2/3 cases occur before age of 15 (median age = 5-6)

• Symptoms: Falling, nausea & vomiting, double vision, headache, eventually trouble moving. If its located on midline child will tend to fall forward or backward

•Other Causes of Cerebellar Damage

• Strokes or tumors affecting cerebellum

• Demyelination due to MS

• Genetically based degenerative disorders (e.g. Friedrich’s ataxia caused by degeneration of spinocerebellar tracts)

• Alcoholic cerebellar atrophy. Cerebellum can also be damaged by some anticonvulsants or chemotherapy.