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12 Cards in this Set
- Front
- Back
General fiber types that carry afferent info to the cerebellum
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1) Climbing fibers- from the contralateral inferior olive
- Directly excite Purkinje cells - Each fiber connects w/ up to 10 P cells 2) Mossy fibers - Indirectly excite Purkinje cells by exciting granule cells. ** Both fiber types also send some collaterals to deep cerebellar nuclei. |
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Cell type that sends efferents out from the cerebellar cortex
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Purkinje cells
- inhibitory output - Project mostly to deep cerebellar nuclei **Those from flocculonodular lobe bypass the deep nuclei & directly connect in the vestibular nuclei. |
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Projections leaving the cerebellum
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1) Inhibitory Purkinje cell axons from the flocculonodular lobe (few)
2) Excitatory axons from the deep cerebellar nuclei (numerous) |
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Functional divisions of the cerebellum
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1) Vestibulocerebellum
2) Spinocerebellum 3) Cerebrocerebellum |
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Vestibulocerebellum
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- Components: Flocculonodular lobe
- Deep nuclei: none - Afferents: 1) Vestibular labyrinth (ipsilateral) 2) Vestibular nuclei (bilateral) - Afferents travel in: Inf. cerebellar ped's - Efferents: Inhibitory, direct from Purkinje's 1) Medial & Superior Vestibular Nuclei (coordinate eye mvmts relative to the head [via vestibular projections to cervical MNs, CN nuclei, & MLF]) 2) Lateral Vestibular Nuclei (influence axial muscles & limb extensors [via lateral vestibulospinal tracts]) - Efferents travel in: Inferior CPs - Major function: Regulation of eye movements, balance, & equilibrium |
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Spinocerebellum: vermal portion
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- Components: Cerebellar Vermis & Fastigial Nuclei= medial division
- Deep nuclei: fastigial - Afferents: 1) Dorsal spinocerebellar tracts, cuneoc., & trigeminoc. (ipsilateral)--> via Inferior CP 2) Ventral spinocerebellar tract (originate ipsi, ascend contra, recross in SCP & finally ipsilateral)--> via SCP 3) Vestibular (bilateral)--> via ICP - Afferents travel in: see above - Efferents: 1) lateral vestibular nuclei (bilaterally) 2) brainstem reticular nuclei - Efferents travel in: ICP - Major function: Influence spinal neurons controlling anti-gravity muscles in proximal limbs & trunk, and head/neck muscles. |
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Cerebrocerebellum
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- Components: Cerebral hemispheres & dentate nucleus
- Deep nuclei: Dentate - Afferents: 1) Cerebral cortex (contralateral) --> via MCP 2) Inferior Olive (contralateral)--> via ICP - Afferents travel in: see above - Efferents: 1) Red nucleus-parvocellular (contra-)--> Inferior olive (ipsi-) **Feedback loop! 2) VA/VL nuclei of thalamus (contra-)--> Motor & non-motor cerebral cortex (ipsi-) - Efferents travel in: SCP - Major function: Fine motor control, and the planning, initiation, & timing of complex movements. (Also likely: "motor memory" role) |
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Spinocerebellum: paravermal portion
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- Components: Paravermal Cortex & Interposed Nuclei= lateral division
- Deep nuclei: interposed (emboliform & globose) - Afferents: 1) Dorsal spinocerebellar tracts, cuneoc., & trigeminoc. (ipsilateral)--> via Inferior CP 2) Ventral spinocerebellar tract (originate ipsi, ascend contra, recross in SCP & finally ipsilateral)--> via SCP - Afferents travel in: see above - Efferents: 1) Magnocellular portion of Red Nucleus (contralateral)--> decussate & descend as Rubrospinal Tract 2) VA/VL nuclei of thalamus (contralateral)--> motor & premotor cerebral cortex - Efferents travel in: SCP - Major function: Influence distal muscles |
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Why do cerebellar lesions produce clinical deficits that are ipsilateral to the lesion?
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- Efferents from the cerebellum to the cortex initially decussate to contralateral thalamus before ascending ipsilaterally to the cerebral cortex.
- Projections from the cerebral cortex decussate in the medulla before descending in their corticospinal tracts. - Projections through thr red nucleus similarly cross. |
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Role of climbing fibers in motor learning
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"error detector"
Only active when a synapse needs to be modified. - Coincident activity of climbing & parallel fibers on the same Purkinje cell= retained lon term= learning. --> Increased climbing fiber activity induces LTD at the parallel/Purkinje cell synapse. --> Decreased CF activity ressults in LTP |
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Effect of a lesion of the oculomotor vermis
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The capability for motor learning is abolished.
In experiment, the surgically weakened eye continues to make undershoot errors w/ no improvement. |
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Intention tremors
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Presence of these can localize the lesion to the cerebellum.
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