BB Lecture 18: Motor system III: Cerebellum

Question 1

What is a key characteristic of the cerebellum?

Answer 1

10% of brain volume volume and 50% of the neurons of the brain

Question 2

What is the function of cerebellum?

Answer 2

• 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

Question 3

What will a lesion in cerebellum result in?

Answer 3

• 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

Question 4

What are the three deep nuclei in the cerebellum?

Answer 4

(from lateral to medial) dentate, interposed and fastigial nuclei

Question 5

How is cerebellum connected to brainstem?

Answer 5

Via the three peduncles

Question 6

Primary fissure

Answer 6

separates anterior and posterior lobe

Question 7

Posterio-lateral fissure

Answer 7

separates the flocculonodular lobe from posterior lobe

Question 8

What is the functional organization of the cerebellum?

Answer 8

a. flocculonodular lobe
b. vermis
c. two hemispheres

Question 9

folia

Answer 9

leaf in Latin

• this is the name given to the folds in cerebellum
• run in medial lateral plane

Question 10

The 3 anatomical lobes

Answer 10

A. Anterior lobe (vermis)
B. Posterior lobe (hemispheres)
C. Flocculonodular lobe (inferior): most highly conserved

Question 11

What is the organization of each individual lobe?

Answer 11

i. central vermis
ii. the lateral zone in hemisphere
iii. the intermediate zone in hemisphere

Question 12

What are the two types of cells within cerebellum?

Answer 12

i. Purkinje cell

ii. Granular cell

Question 13

Purkinje cell:

Answer 13

-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!

Question 14

Granular cells

Answer 14

• 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

Question 15

What are the two inputs into the cerebellum? What do they have in common?

Answer 15

i. climbing fibers
ii. mossy-parallel fibers
Both are excitatory and glutamatergic

Question 16

Climbing fibers:

Answer 16

• 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

Question 17

Mossy fibers:

Answer 17

• 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

Question 18

Where does dentate nucleus send axons to? Function?

Answer 18

M1 and premotor cortices

Function: motor planning

Question 19

M1 and premotor cortices
Function: motor planning
Where does interposed nucleus send axons to? Function?

Answer 19

Lateral descending systems

Function: motor execution

Question 20

Where does fastigial nucleus send axons to? Function?

Answer 20

Medial descending systems

Function: motor execution

Question 21

Where do axons from vestibulocerebellum (flocculonodular) terminate? Function?

Answer 21

Vestibular nuclei in pons/medulla of brainstem

Function: balance and eye movement

Question 22

What are the three main function regions of the cerebellum?

Answer 22

i. Vestibulocerebellum
ii. Spinocerebellum
iii. Cerebrocerebellum

Question 23

What is the function of the Spinocerebellum?

Answer 23

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

Question 24

What is the function Cerebrocerebellum?

Answer 24

Motor planning
Active BEFORE each movement during
Dentate  VL (ventrolateral…thalamus)  association, premotor and M1 (contralateral projection via SCP)
-inputs from the cerebral cortex

Question 25

What is the function of the Vestibulocerebellum?

Answer 25

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)

Question 26

Pontine nuclei:

Answer 26

where mossy fibers come from and innervates the cerebellar granular cells

Question 27

Viscoelasticity

Answer 27

property of materials that exhibit both viscous and elastic characteristics when undergoing deformation

Question 28

What does processing of proprioceptive information in cerebellum responsible for?

Answer 28

Regulates anticipatory and viscoelastic forces associated to multi-joint movements and generation of predictive muscle contraction

Question 29

Does the cerebellum have a role in LEARNING motor tasks? And if so what’s the MOA?

Answer 29

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

Question 30

What are the three categories of cerebellar symptoms after lesion

Answer 30

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