Functional Anatomy Of The Cerebellum Flashcards
The cerebellum functions as a …
Rapid, corrective feedback loop smoothing and coordinating movements
The motor plan leaves…
The cortex (intended movement) and goes to the basal nuclei and cerebellum (actual movement)
The cerebellum overvie w
Programmes ballistic movements - precise timing and appropriate patterns of skeletal muscle contraction
Compares intended and actual movement
Corrects ongoing movement
Activity occurs subconsciously
Motor learning patterns shift from the conscious to unconscious
Information from:
Somatosensory
Visual, auditory, vestibular, proprioceptive
Describe the anatomy of the cerebellum
Situated in post cranial fossa and covered superiorly by the tentorium cerebellum
Located dorsal to the pons and medulla
Accounts for 11% of the brain mass
Two cerebellar hemispheres L&R joined medially by the vermis
Internal white matter - arbor vitae
External grey matter folia - transversely arranged gyri
Each hemisphere divided in to 3 lobes by primary and posterolateral fissures
What are the 3 lobes of the cerebellum
Anterior
Posterior
Flocculonodular
A tier and posterior lobes are dived further into…
Zones
Vernal Zoe - occupies the vermis
Intermediate (paravermal) zone - lies on each side of the vermis, occupying the medial regions of the cerebellar hemispheres
Lateral zone - lies lateral to the intermediate zone
What are the cerebellar peduncles
Three paired fibre tracts connect the cerebellum to the brainstem
Superior - connect cerebellum -> midbrain
Middle - connect cerebellum -> post and to the axis of the brainstem
Inferior - connect cerebellum -> medulla
Describe the superior peduncles
To the midbrain
Fibres originate from neurons in the deep cerebellar nuclei and communicates with the motor cortex via the midbrain and the Diencephalon (thalamus)
Describe the middle peduncles
To the pons
Cerebellum receives info advising it of voluntary motor activities initiated by motor cortex
Describe the inferior peduncles
To the medulla
Afferent conveying sensory info from muscle proprioceptors thorughout the body and from the vestibular nuclei of the brainstem (medulla oblongata)
What are the 3 major function divisions of the cerebellum
Vestibulocerebellum - composed of the flocculonodular lobe
Spinocerebellum - composed of th vermis and paravermal zone
Cerebrocerebellum - composed of the lateral zones of the cerebellar hemispheres
Anterior lobe is responsible for …
The regulation of muscle tone, coordination of skilled voluntary movement
Posterior lobe is responsible for…
Planning and initiation of voluntary activity
Flocculomodular lobe is responsible for
Maintenance of balance, control of eye movement
What are the spinocerebellar tracts
Posterior (dorsal) - enters cerebellum via inf cerebellar peduncle
Anterior (ventral) - enters cerebellum via the superior cerebellar peduncle
Cuneoerebellar tract - enters cerebellum via inf cerebellar peduncle
Describe the inferior olivary nuclei
Receives info from cutaneous Afferents, joint afferents and muscle spindles and from here axons pass to the contralateral cerebellar Cortex via the inferior cerebellar peduncle
Wil also receive axons from the sensorimotor cortex directly and indirectly via the red nucleus
Describe the deep pontine nuclei
Primary route by which the cerebral cortex communicates with the cerebellum via the basilar pons
Describe the reticular formation
Regulates spinal reflexes - provides a key input to the cerebellum that relates to the manner in which reticular neurons regular extensor motor tone at any given time
Several of the nuclei within this receive input from the sensorimotor cortex serving as a relay for cerebral cortical inputs to the cerebellum
Describe the Tectum
Cerebellum also receives fibres arising from the sup. And inf. colliculi of the Tectum to provide visual and auditory information respectively
Do so by projecting to the pontine nuclei, which in turn go through the ,idle cerebellar peduncle to the cerebellar cortex
Describe the red nucleus
Serves as a relay from the sensorimotor cortex to the spinal cord via the rubrospinal tract
In a similar manner the sensorimotor cortex can provide signals to the cerebellar cortex via the red nucleus
Describe the trigeminal system
Secondary proprioceptive fibres associated itch muscle spindle activity of the face and jaw reach the cerebellum through the mesencephalic trigeminal nucleus
Describe the vestibular system
Via the ICP to the flocculonodular lobe
What fibres does the middle cerebellar peduncle carry
Only afferent fibres
Where do inputs go?
Deep cerebellar nuclei
What are the deep cerebellar nuclei?
Separated from the cerebellar cortex by the white tater are underlying, deep, cerebellar nuclei whic are represented bi laterally. Moving laterally to medially:
Dentate nucleus
Emboliform
Globose
Fastigal
(Don’t Eat Greasy Food)
Dentate nuclei
Project contralaterally though the superior cerebellar peduncle to neurons in the contralateral thalamus and from thalamus to motor cortex
Function: influence planning and initiation of voluntary movement
Emboliform and Globose nuclei
Project mainly to the contralateral red nuclei and a small group is projected to the motor cortex
Function: Red nuclei -> rubrospinal tract control of proximal limb muscles
Fastigial nuclei
Project to the vestibular nuclei and to the pontine and medullary reticular formation
Function: vestibulospinal and reticulospinal tracts
Overview of cerebellar output/efferent
Cerebellar cortex ->deep nuclei _
->thalamus -> cerebral cortex
-> vestibular nuceli
-> inferior olive
-> red nucleus
Cerebellar cytoarchitecture
Each folium - cortex and deep white matter (projections of Purkinje cell fibres to deep cerebellar nuclei)
3 layered cortex
What are the 3 layers of the cortex
Molecular
Purkinje
Granule
Describe the granular cell layer
Granule cells are abundant within this layer
Contains 3-5 dendrites arranged in a claw like appearance
Receive mossy fibre afferents.
Axons travel to the molecular layer where they branch in a T junction to form the parallel fibres.
Golgi cells are also found in the granular layer and their processes radiate to all other cell layers. They are inhibitory GABA-ergic interneurons and their cell body is usually located close to the Purkinje cell layer. Golgi cells synapse with granule cells and mossy fibres.
Describe the Purkinje cell layer
Is one cell thick and contains the Purkinje cell
The Purkinje neuron is the largest cell in the cerebellar cortex.
Dendrites emerge from its neck and thick dendritic trees are directed into the molecular layer
They receive excitatory input from granule cells via parallel fibres and climbing fibres.
The axons of the Purkinje terminate in one of the deep cerebellar nuclei.
Purkinje cells located in the vermal region project to the fastigial nucleus,
Purkinje cells located in the hemispheres project to the dentate nucleus
Purkinje cells located in the paravermal region project to the interposed nuclei.
Purkinje cells are inhibitory
Describe the molecular cell layer
contains the dendrites of Purkinje cells, parallel fibres (axons of granule cells) and two other cell types, basket and stellate cells.
Basket and stellate cells are inhibitory GABA-ergic cells that synapse with Purkinje cells.
Receive input from parallel and climbing fibres.
What are mossy fibres
All cerebral afferents originating from all sources except the inferior olivary nuclear complex
Include afferents from the spinal cord, posterior column nuclei, trigeminal system, pontine ad vestibular nuclei
Synapse with Golgi cells and granule cell dendrites
Are excitatory fibres that utilise glutamate as their NT
Describe climbing fibres
Arise from the inf olivary nucleus and ascend thorugh the granular and Purkinje cell layers to reach the molecular layer
Each individual fibre forms and excitatory synapse with one Purkinje cell
This one to one relationship is key in motor learning
Climbing fibres are excitatory and use aspartate as their NT
Both mossy and climbing fibres…
Excite their target neurons in the cerebellar cortex but also provide excitatory collaterals to the deep cerebellar nuclei
How does micro-cuitry work? Climbing fibres…
Excite the purkinje cells
How does micro-cuitry work? Mossy fibres…
Excite the granule cells
How does micro-cuitry work? Granule cells….
Make excitatory contact with the purkinje cells
How does micro-cuitry work? Purkinje cells
Tonic inhibition on the activity of the neurons of the cerebellar nuclei
-> all excitatory inputs converted to he inhibition
-> removing the excitatory influence of the cerebellar inputs (erasing)
All output from the cerebellar cortex is through the …… which is ……. Yet the output as a whole is….
Purkinje cell which is inhibitory to the deep cerebellar nuclei yet the output from the cerebellum as a whole is excitatory
Climbing fibres and mossy fibres send….. which results in……
Send collaterals to the deep cerebellar nuclei which results in immediate activation of the cerebellar nuceli
Activation of deep cerebellar nuclei is followed by
Inhibiton mediated by the Purkinje cell
Purkinje cell activation is mediated by the action of the …
Golgi cells on the parallel fibres
Excitation of the purkinje cell by the parallel fibres is …
Short
When the excitation of the ……… ceases there is an increase in
deep cerebellar nuclei excitation
Purkinje cell
Release of inhibition known as
Disinhibition
Signals transmitted to the deep cerebellar nuclei to its target neurons in the brain stem/thalamus after mossy or climbing fibres consists of….
Initial activation then inhibition followed by disinhibition
This pattern of discharge becomes the
Coded message transmitted from the cerebellum to its distal targets
