The Cerebellum Flashcards
Describe what the cerebellum does
It functions as a rapid corrective feedback loop smoothing and coordinating movements
Where does the cerebellum get its information?
Somatosensory areas
Visual
Auditory
Vestibular
Proprioceptive
Give a more detailed description of what the cerebellum does
Programmes ballistic movements - precise timing and appropriate patterns of skeletal muscle contraction
Compares intended and actual movements
Corrects ongoing movements
Activity occurs subconsciously
Motor learning pattern shift from conscious to unconscious
Where is the cerebellum found?
Situated in the posterior cranial fossa and covered superiorly by the tentorium cerebelli
Located dorsal to the pons and medulla
Accounts for 11% of the brains mass
Describe the structure of the cerebellum
Two hemispheres joined medially by the vermis
Internal white matter - arbor vitae
External grey matter (foila) - transversely arranged gyri
How in the cerebellum divided
By the primary and posterolateral fissures
Ant lobe
Post lobe
Flocculonodular lobe
What areas are the Ant and Post lobes further divided to?
Vermal zone - occupies the vermis
Intermediate (paravermal) zone - lies on each side of the vermis, medial regions of the cerebellar hemispheres
Lateral zone - lies lateral to the intermediate zone
What are cerebellar peduncles?
Paired fibre tracts that connect the cerebellum to the brainstem
Name the 3 cerebellar peduncles
Superior - cerebellum to midbrain
Middle - cerebellum to pons and the axis of the brainstem
Inferior - cerebellum to medulla
Describe the superior peduncles
Fibres originate from the neurons in the deep cerebellar nuclei and communicates with the motor cortex via the midbrain and the Diencephalon (thalamus)
Describe the middle peduncles
Cerebellum receives info advising it of voluntary motor activities initiated by the motor cortex
Describe the inferior or peduncles
Afferents conveying sensory info from muscle proprioceptors throughout the body and from the vestibular nuclei of the brainstem (medulla oblongata)
What are the functions divisions of the cerebellum?
Vestibulocerebellum- composed of the flocculonodular lobe
Spinocerebellum- composed of the vermis and paravermal zones
Cerebrocerebllum- composed of lateral zones
What does the vestibulocerebellum do?
Maintenance of balance and control of eye movement
What does the spinocerebllum do?
Regulation of muscle tone, coordination of skilled voluntary movement
What does the cerebrocerebellum do
Planning and initiation of voluntary activity
What are the spinocerebllar?
Post spinocerbellar tract
Ant spinocerebellar tract
Cuneocerebellar tract
Where does the Post spinocerebellar tract enter?
Enters the cerebellum via the inferior cerebellar peduncle
Where does the Ant spinocerebellar tract enter?
Enters the cerebellum via the superior cerebellar peduncle
Where does the cuneocerebellar tract enter?
Enters the cerebellum via the inferior cerebellar peduncle
Where does the inferior olivary nucleus receive info from?
Cutaneous afferents
Joint afferents
Muscle spindles
Then axons pass contrallaterally through the inferior peduncle
Also axons from the sensorimotor cortex directly and indirectly via the red nucleus
What is the deep pontine nuclei important for?
The primary route by which the cerebral cortex communicates with the cerebellum
(The basilar pons)
What does the reticular formation do?
Regulates spinal reflexes
Important for which reticular neurons regulate extensor motor tone at any given time
Where does the reticular formation receive info from?
From the sensorimotor cortex which serves as a relay for cerebral cortical inputs to the cerebellum
How does the tectum communicate with the cerebellum?
Through its superior and inferior colliculi
They provide visual and auditory info respectively
By projecting to the pontine nuclei which then go through the middle cerebellar peduncle to the cerebellar cortex
What does the red nucleus do?
Serves as a relay from the sensorimotor cortex to the spinal cord via the rubrospinal tract
Sensorimotor cortex may also send signals through the red nucleus
Describe the trigeminal system during cerebellar input
Secondary proprioceptive fibres associated with muscle spindle activity of the face and jaw reaching the cerebellum through the mesencephalic trigeminal nucleus
How does the vestibular system influence cerebellar input?
Via the ICP to the flocculonodular lobe
What are the deep cerebellar nuclei?
Don’t Eat Greasy Food
Dentate nucleus
Emboliform nucleus
Globose nucleus
Fastigal nucleus
Describe the Dentate nuclei
Project contralaterally through the superior cerebellar peduncle to neurones in the contralateral thalamus and thalamus to motor cortex
What is the function of the Dentate nucleus?
To influence planning and initiation of voluntary movement
Describe the emboliform nucleus
Project mainly to the contralteral red nuclei and small group is projected to the motor cortex
What is the function of the emboliform nucleus?
Red nuclei to rubrospinal tract control of proximal muscles
Describe the fastigial nuclei
Project to the vestibular nuclei and to the pontine and meduallary reticular formation
What is the function of the fastigial nuclei?
The vestibulospinal tracts
Recticulospinal tracts
What is another name for the posterior lobe of the cerebellar hemispheres?
The neocerebellum
What are the three layers to the cortex of the cerebellum?
Molecular layer - Parallel fibres from granule cells
Purkinje cell layer - Single cell thick
Granule cell layer - granule cell bodies
What cells are found in the granular cortex level of the cerebellum?
Abundant with granule cells
But also have Golgi cells - their processes radiate to all other cell layers
(Inhibitory GABA-ergic interneurons - cell bodies found close to the purkinje layer
What is the structure / pathway if the granular cell layer?
3-5 dendrites arranged in a claw like appearance
Receive mossy fibre afferents
Axons travel to the molecular level where they branch in a T junction to form parallel fibres
Golgi and granule cells synapse with mossy fibres
What cells are found in the molecular layer of the cortex of the cerebellum?
Dendrites if purkinje cells
Parallel fibres (granule axons)
Basket cells
Stellate cells
What are basket and stellate cells?
Inhibitory GABA-ergic cells that synapse with perkinjes
Receive input from parallel and climbing fibres
Describe the purkinje cell layer of the cerebellum
It is one cell thick and contains the perkinje cell (largest cell of the cerebellar cortex)
Dendrites emerge from its neck and thick dendritic trees are directed into the molecular layer
What input does the purkinje cell layer receive?
Receive excitatory input from granule cells via parallel and climbing fibres
Where do purkinje cell axons terminate?
Terminate in one of the feel cerebellar nuclei
What do purkinje cells do?
Vermal zone - project to the fastigial nucleus
Hemispheres - project to the Dentate nucleus
Paravermal region - project to interposed nuclei
Purkinje cells are inhibitory
What are mossy fibres?
Are cerebellar afferents originating from all sources except the inferior olivary nuclear complex
What do mossy do?
Synapse with Golgi and granule cell dendrites
They are excitatory fibres that utilise glutamate as the neurotransmitter
List some of the places mossy fibre afferents come from
Spinal cord
Post column nuclei
Trigeminal system
Pontine and vestibular nuclei
What are climbing fibres?
They are excitatory fibres that use aspartate as their neurotransmitter
Arise from the inferior olivary nucleus and ascend through the granular and Purkinje layers to reach the molecular layers
What is the synapse ratio of climbing fibres to Purkinje cells?
Each individual climbing fibre forms an excitatory synapse with one purkinje cell
This one to one ration is key in motor learning
What are the only output cells of the cerebellar cortex?
Purkinje fibres
So although mossy and climbing fibres are excitatory, purkinjes are inhibitory so the only output of the cerebellar cortex is inhibitory
The excitement level of the mossy/ climbing fibres will determine the level of inhibition
What is tonic inhibition?
It’s how purkinje cells function
All excitatory inputs will be converted to inhibitory
Removing the excitatory influence of the cerebellar inputs
How can the overall output of the cerebellum be excitatory if the only output from the cerebellar cortex is inhibitory?
Climbing and mossy fibres send collaterals to the deep cerebellar nuclei which results in immediate activation of the cerebellar nuclei
Describe the process of inhibition
Collateral excitation if the deep cerebellar nuclei is followed inhibition mediated by purkinje cells, which are activated by Golgi and parallel fibres
When purkinje inhibition ceases there can be an increase in deep nuclei excitation
What is the basic explanation of cerebellar output?
Initial activation
Inhibition
Disinhibition
