Cerebellum & Motor Activity (Lecture Apr 26, 2010)

Front 1

General fiber types that carry afferent info to the cerebellum

Back 1

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.

Front 2

Cell type that sends efferents out from the cerebellar cortex

Back 2

Purkinje cells

- inhibitory output
- Project mostly to deep cerebellar nuclei

**Those from flocculonodular lobe bypass the deep nuclei & directly connect in the vestibular nuclei.

Front 3

Projections leaving the cerebellum

Back 3

1) Inhibitory Purkinje cell axons from the flocculonodular lobe (few)

2) Excitatory axons from the deep cerebellar nuclei (numerous)

Front 4

Functional divisions of the cerebellum

Back 4

1) Vestibulocerebellum
2) Spinocerebellum
3) Cerebrocerebellum

Front 5

Vestibulocerebellum

Back 5

- 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

Front 6

Spinocerebellum: vermal portion

Back 6

- 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.

Front 7

Cerebrocerebellum

Back 7

- 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)

Front 8

Spinocerebellum: paravermal portion

Back 8

- 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

Front 9

Why do cerebellar lesions produce clinical deficits that are ipsilateral to the lesion?

Back 9

- 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.

Front 10

Role of climbing fibers in motor learning

Back 10

"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

Front 11

Effect of a lesion of the oculomotor vermis

Back 11

The capability for motor learning is abolished.

In experiment, the surgically weakened eye continues to make undershoot errors w/ no improvement.

Front 12

Intention tremors

Back 12

Presence of these can localize the lesion to the cerebellum.