BB Lecture 18: Motor system III: Cerebellum Flashcards
What is a key characteristic of the cerebellum?
10% of brain volume volume and 50% of the neurons of the brain
What is the function of cerebellum?
- evaluates disparities between intention and action and generates correction signals to cortex and brainstem
- receives efferent copy of EVERY motor command (execution AND planning)
- afferent input from proprioceptive systems
- output to motor and premotor cortex via thalamus
What will a lesion in cerebellum result in?
- loss of spatial accuracy and temporal coordination of movement
- impairment of balance and loss of muscle tone
- NO loss of sensory thresholds or strength of muscle contraction
What are the three deep nuclei in the cerebellum?
(from lateral to medial) dentate, interposed and fastigial nuclei
How is cerebellum connected to brainstem?
Via the three peduncles
Primary fissure
separates anterior and posterior lobe
Posterio-lateral fissure
separates the flocculonodular lobe from posterior lobe
What is the functional organization of the cerebellum?
a. flocculonodular lobe
b. vermis
c. two hemispheres
folia
leaf in Latin
- this is the name given to the folds in cerebellum
- run in medial lateral plane
The 3 anatomical lobes
A. Anterior lobe (vermis)
B. Posterior lobe (hemispheres)
C. Flocculonodular lobe (inferior): most highly conserved
What is the organization of each individual lobe?
i. central vermis
ii. the lateral zone in hemisphere
iii. the intermediate zone in hemisphere
What are the two types of cells within cerebellum?
i. Purkinje cell
ii. Granular cell
Purkinje cell:
-main cells in cerebellum
-it is similar to pyramidal cells in cortex in the sense that these guys are the output cells
-they are INHIBITORY
-GABAergic
Climbing fibers activate purkinje which inhibits the deep cerebellar nuclei
One purkinje cell can receive up to one million granule cell synapses!
Granular cells
- small round cells that are super tightly packed
- dendrites of granular cells are where the mossy fibers synapse
- send axons to molecular layer forming the parallel fibers
- parallel fibers travel a long distance…PARALLEL TO THE FOLIA
- a single granule cell contacts an average of 500 purkinje cells because of the parallel fiber growth
What are the two inputs into the cerebellum? What do they have in common?
i. climbing fibers
ii. mossy-parallel fibers
Both are excitatory and glutamatergic
Climbing fibers:
- originate in the inferior olive and terminate in the dendrites of Purkinje cells
- climbing fibers wrap around the dendrites of purkinje cells like a vine on a tree making hundreds of synaptic contacts and constituting an extremely safe synapse.
- little divergence…once climbing fiber with send output to 5-10 purkinje cells
- one purkinje cells get one climbing fiber
Mossy fibers:
- fibers from all sensory modalities
- HIGHLY divergent
- originate from nuclei in the spinal cord and brainstem and carry sensory information from the periphery as well as information from the cerebral cortex
- terminate as excitatory glutamatergic fibers on granule cells
Where does dentate nucleus send axons to? Function?
M1 and premotor cortices
Function: motor planning
M1 and premotor cortices
Function: motor planning
Where does interposed nucleus send axons to? Function?
Lateral descending systems
Function: motor execution
Where does fastigial nucleus send axons to? Function?
Medial descending systems
Function: motor execution
Where do axons from vestibulocerebellum (flocculonodular) terminate? Function?
Vestibular nuclei in pons/medulla of brainstem
Function: balance and eye movement
What are the three main function regions of the cerebellum?
i. Vestibulocerebellum
ii. Spinocerebellum
iii. Cerebrocerebellum
What is the function of the Spinocerebellum?
Motor execution
Compares the motor commands with motor execution and issues correcting commands DURING movement
-corresponds to the vermis, lateral and medial descending system
Limbs: interposed VL (ventro lateral) M1
Axial: fastigial medial motor systems of the brainstem
What is the function Cerebrocerebellum?
Motor planning
Active BEFORE each movement during
Dentate VL (ventrolateral…thalamus) association, premotor and M1 (contralateral projection via SCP)
-inputs from the cerebral cortex
What is the function of the Vestibulocerebellum?
combines acceleration of head with visual inputs to coordinate balance
- visual and auditory inputs
- used for balance and eye movement
- most primitive
- they project DIRECTLY out of cerebellum to vestibular nuclei (so only one with a deep nuclei that is outside of cerebellum)
Pontine nuclei:
where mossy fibers come from and innervates the cerebellar granular cells
Viscoelasticity
property of materials that exhibit both viscous and elastic characteristics when undergoing deformation
What does processing of proprioceptive information in cerebellum responsible for?
Regulates anticipatory and viscoelastic forces associated to multi-joint movements and generation of predictive muscle contraction
Does the cerebellum have a role in LEARNING motor tasks? And if so what’s the MOA?
Yes
Activity in the dentate nucleus increases considerably when subjects are asked to identify the object rather than just grab it
Significance: cognitive demands increase cerebellar involvement
What are the three categories of cerebellar symptoms after lesion
I. hypotonia: lack of resistance to passive displacement of limbs, pendular reflexes
II. Ataxia (lack of coordination): eye movmeents, walking, delay to initiate movments, dysmetria, dysdiadochokinesia (lack of regularity), decomposition of movement
III. intentional tremor
