12. Cerebellum Flashcards
Functions of the cerebellum
- MOVEMENT REGULATION (corrects disparities between intended and ongoing actions, smooths execution) - does NOT initiate movement
- involved in all phases of GAIT
- Equilibrium
- Eye movements
- Regulation of muscle tone and posture
Anatomy
Location of the cerebellum
- Internal to occipital bone
- Separated from cerebrum via tentorium cerebelli
- Rostral to medulla oblongata
- Dorsal to pons
Anatomy
- Describe the gross topographical vs developmental divisions of the cerebellum
- Vermis centrally
- Hemispheres laterally
- Large body dorsally
- Small flocculonodular lobe ventrally
- Body divided in rostral and dorsal lobe
Anatomy
- The body is separated from flocculonodular lobe via the ____ fissure
- The body is divided into a rostra and caudal lobe via the ____ fissure
- B/F = uvulonodular fissure
- R/C lobes = primary fissure
Anatomy
Anatomy of flocculonodular lobe
- 1 NODULUS: on caudal vermis, centrally
- 2 FLOCCULUS: on each hemisphere, laterally
- Joined via flocculonodular peduncle
Anatomy
Vestibulocerebellum - Phylogenetic name, topographical components, afferents (general), role
Table slide 11
- Archicerebellum
- Flocculonodular lobe
- A: vestibula system
- Equilibrium + reflexive eye movements in response to head position
Spinocerebellum - Phylogenetic name, topographical components, afferents (general), role
- Paleocerebellum
- Rostral + caudal vermis (except nodulus) + paraflocculus
- Spinal cord (spinocerebellar tracts)
- Posture, locomotion, gaze
Anatomy
Pontocerebellum or cerebrocerebellum - Phylogenetic name, topographical components, afferents (general), role
- Neocerebellum
- Middle vermis + rest of hemispheres
- Cerebrum (via pons/middle cp)
- Skilled mvts of the limbs
Difference between folia and lobule
- FOLIUM: ridge of cerebellar cortex extending from one hemisphere to the other across midline
- LOBULE: group of folium (vermal + horizontal)
Name and location of cerebellar white matter
- Cerebellar medulla
- In the cerebellum core
- Form arbor vitae = extensions overlying each folia
Anatomy
3 CEREBELLAR PEDUNCLES: name, locate, brainstem connection, afferents vs efferents
Slide 15
From medial to lateral:
* Rostral: midbrain, mainly efferents
* Caudal: medulla + SC, mainly afferents
* Medial: pons, only afferents (transverse fibers)
Anatomy
3 CEREBELLAR NUCLEI: name, locate
From medial to lateral:
* Fastigial
* Interposed
* Dentate (lateral)
Anatomy
Cerebellar nuclei sends inhibitory or excitatory outputs?
Excitatory
Anatomy
FASTIGIAL NUCLEUS: Afferents and efferents
Works with VERMIS + FLOCCULONODULAR lobe
Afferents:
* Vermis (spinocerebellar inputs from axial muscles)
* Flocculonodular lobe (vestibular inputs)
Efferents (via cpp):
* Vestibular nuclei
* Reticular formation
Anatomy
INTERPOSED NUCLEUS: Afferents and efferents
Afferents:
* Paraflocculus (spinocerebellar inputs from limbs)
Efferents (via rcp)
* Red & olivary nuclei (midbrain)
* Reticular formation
Anatomy
DENTATE (lateral) nucleus: Afferents and efferents
Works with the lateral zone
Afferents:
* Contralateral motor cortex, via pontocerebellar fibers (mcp)
Efferents (via rcp):
* VLN (thalamus) - back to motor cortex
* Red nucleus (midbrain)
* Olivary nucleus (medulla)
* Pontine nucleus (pons)
* Reticular formation
* Pallidum
De lahunta; VLN, red nucleus, reticular formation, pallidum
Development
Describe briefly the steps of cerebellar development
Slide 21
- Arises from growth of ALAR PLATE into a RHOMBIC LIP that contains GERMINAL CELLS
- 1st group of germinal cells mature into PURKINJE cells, forming the purkinje layer (middle)
- 2nd group continues to divide and form that EXTERNAL GERMINAL layer.
- Inner cells migrate and form the GRANULAR layer;
- Others form the STELLATE cells of the molecular layer (?) they are in the granular layer…
- Remaining cells form EPENDYMAL cells lining 4th ventricle
Development
External germinal layer remains visible when post-natally in dogs and cats?
- 84 days in kittens
- 75 days in puppies
Histology
Name the 3 cerebellar cortical layers
- MOLECULAR: axons and telodendria of granular cells + rare basket cells
- PURKINJE: large, flask-shaped purkinje cells
- GRANULAR: mass of granule cells + scattered golgi (stellate) cells
Name 4 cerebellar neurons (have cell bodies in the cerebellum)
- Basket cells
- Purkinje cells
- Granule cells
- Golgi (stellate) cells
PURKINJE neurons: cell body, dendrites, axons
- Dendrite: molecular layer
- Axons (-, GABA): cerebellar nuclei (most), vestibular nuclei (those from flocculonodular lobe)
GRANULE cells: cell body, dendrites, axons
- Granular layer
- Dendrites: receive + inputs from Mossy fibers
- Axons (+, glutamate): bifurcate as parallel fibers in the molecular layer, intersect with Purkinje dendrites (activate those in exact same plane)
Golgi (Stellate) cells: cell body, dendrites, axons
- Granular layer
- Dendrites: + inputs from mossy and parallel fibers
- Axons (-, GABA /glycine): synapse on granule cells (feedback inhibition)
Basket cells: cell body, dendrites, axons
- Molecular layer
- Dendrites: + inputs from parallel fibers
- Axons (-, GABA): inhibit purkinje cell bodies in immediately adjacent plane
Name the two afferent fibers of the cerebellum
Mossy & climbing fibers
Common features of mossy and climbing fibers
- Both excitatory (mossy = ACh, Climbing = aspartate)
- Become mossy and climbing fibers only once in the cerebellum
- Send + collaterals on cerebellar nuclei as they ascend
Mossy fibers: origin and influence on Purkinje neurons
- Spinal cord + brainstem;
- Synapse on golgi cells + granular cells
- Influence Purkinje neurons indirectly (via granule cells, Golgi cells, basket cells)
Note: activation of GOLGI cells cause inhibition of granule cells = less activation of purkinje cells = disinhibition of cerebellar nuclei
Note: activation of GRANULE cells = more activity of purkinje cells = inhibition of cerebellar nuclei
Climbing fibers: origin and influence on purkinje neurons
- Olivary nucleus (integration from extrapyramidal system - red nucleus, reticular formation, spinal cord proprioception)
- Entwine / activate purkinje neurons directly
Name the afferent pathways
- 4 spinocerebellar tracts (general proprioception)
- Ipsilateral vestibulocerebellar tracts (special proprioception)
- Tectocerebellar tracts (special somatic afferents; visual + auditory)
- Pyramidal & extrapyramidal tracts (UMN)
Spinocerebellar: ipsilateral
Vestibulocerebellar: ipsilateral
Pyramidal: via controlateral pontine nuclei
Extrapyramidal: via controlateral olivary nucleus
Climing fibers: extrapyramidal tracts
Mossy fibers: all others
What are the efferent cerebellar fibers?
Purkinje fibers (gaba) - most to cerebellar nuclei, some (flocculonodular) to VN
Cerebellar nuclei are…
* Initially activated by ?
* Inhibited by ?
* Disinhibited by ?
- Mossy and climing fibers
- Purkinje fibers
- Golgi (stellate) cells
Cerebellar efferents - Neuron 1-3
Neuron 1: Purkinje neurons (cerebellar cortex)
Neuron 2: Cerebellar nuclei
Neuron 3: ipsi VN, contra thalamus, reticular formation, red nucleus, tectum..
Decussations - all tracts decussate in and out of the cerebellum, EXCEPT
Vestibular feedback circuits
