Problem 3

Question 1

How does the Cerebellum influence movement ?

Answer 1

By modifying the activity patterns of the upper motor neurons

–> efferent cells don’t project directly to local circuits of brainstem + spinal cord

Question 2

Organization of the cerebellum ?

Name the major division of the cerebellar hemispheres.

Answer 2

1. Cerebrocerebellum
2. Spinocerebellum
3. Vestibulocerebellum

Question 3

What is the primary function of the cerebellum?

Answer 3

To detect the difference or “motor error” between an intended movement and the actual movement

–> then reducing the error thrust its influence on upper motor neurons

Question 4

Cerebrocerebellum

Answer 4

Regulates highly skilled movements, especially planning + execution of complex movement

–> occupies the lateral cerebellar hemispheres + receives input indirectly from many areas of the cortex

Question 5

Spinocerebellum

Answer 5

Concerned with movements of distal (paramedian) and proximal (median (vermis)) muscles + eye movements

–> occupies the median zone of the CH + receives input directly from the Spinal cord

Question 6

Vestibulocerebellum

Answer 6

Regulates the movements underlying posture and equilibrium + vestibule-ocular reflex

–> occupies the caudal-inferior lobes + receives input from vestibular nuclei in brainstem

Question 7

The connections between the cerebellum + other parts of the NS occur by way of 3 large pathways.

Name them

Answer 7

1. Superior cerebellar peduncle
2. Middle cerebellar peduncle
3. Inferior cerebellar peduncle

–> white matter tracts

Question 8

Superior cerebellar peduncle

Answer 8

1. Neurons are in the deep cerebellar nuclei
2. Project to upper motor neurons of superior colliculus
3. After relay in thalamus, they also project to primary motor + pre-motor areas of cortex

–> descending/efferent pathway

Question 9

Middle cerebellar peduncle

Answer 9

1. Neurons are in the base of the contralateral pons (pontine nuclei)
2. Receive input from almost all areas of the cortex + superior colliculus
3. Transverse pontine fibers cross its midline to enter cerebellum

–> ascending/afferent pathway

Question 10

Inferior cerebellar peduncle

Answer 10

Smallest but most complex of them, containing multiple afferent + efferent pathways

Question 11

What is the largest source of input that reaches the cerebellum ?

In addition, name the specific destination.

Answer 11

1. Cerebral cortex

2. Cerebrocerebellum

Question 12

How does the cerebellum make sure that our movements are balanced + smooth ?

Answer 12

1. Receives info about what the actual motor plan is via afferent nerves from the respective areas in the cortex
2. It receives info from muscle spindles as to where the body parts are (to compare that to the plan)
3. Then it sends feedback to the motor areas which then can use this info to be better at doing their job

Question 13

Cerebellar pathway

Ascending

Answer 13

Are destined for pre-motor + associational cortices of the FL, thus motor planning

1. Closed loop
   - -> project to non-motor areas, from which signals originate
2. Open loop
   - -> get input from multiple areas; output to motor cortices

AND: both run in parallel

Question 14

Spinocerebellar pathway

Ascending

Answer 14

Are directed to upper motor neurons, which are responsible for executing movement

• -> 1. lateral interposed nuclei
  2. Superior peduncle
  3. Thalamus + FL

Question 15

Spinocerebellar pathway

Descending

Answer 15

Are directed to upper motor neurons responsible for executing movements

• -> 1. Fastigial nuclei (vermis)
  2. Inferior peduncle
  3. Reticular formation + vestibular complex

Question 16

Vestibulocerebellar pathway

Descending

Answer 16

Goes from

1. Inferior peduncle
2. Vestibular complex

–> which governs the moment of eyes, head + neck to compensate for linear vs rotational accelerations of the head

Question 17

Purkinje cells

Answer 17

Are the destination of afferent pathways

–> refer to huge inhibitory dendrites that receive input from parallel fibers

when we move they stop firing because they are tonically active

Question 18

The cerebellum receives direct input from … ?

Answer 18

1. Inferior Olive
2. Climbing fibers
3. Purkinje cells + deep nuclei

Question 19

How do local circuit neurons modulate the inhibitory output of purkinje cells ?

Answer 19

By inhibiting them after they received the excitatory input from parallel fibers

–> involves

1. Basket cells
   - -> lateral inhibition that may focus the spatial distribution of purkinje cell activity
2. Stellate cells

Question 20

How is ongoing movement coordinated by the cerebellum ?

Answer 20

1. Neurons fire selectively for contraction vs. relaxation of specific muscles, positions of joints + direction
2. Purkinje and deep nuclei cells recognise potential errors by comparing incoming patterns of activity concurrently available to both cells
3. Deep nuclei send the correcting signals to upper motor neurons

Question 21

Timing hypothesis

Answer 21

Suggests that the cerebellum is critical for sensorimotor learning because it generates predictions that are temporally precise

1. cortical areas select effectors while cerebellum supplies the precise timing needed for activating these effectors
2. Lesions are most disruptive to highly practiced movements, which present the greatest need for precise timing
   e. g.: classical conditioning example with airpuff

Question 22

State estimate

Answer 22

Is calculated by the brain and is a prediction of the change in motor state

–> occurs by combining sensory info about the last known position with predictions of it’s responses to recent movement commands

Question 23

Forward model

Answer 23

Rapidly predicts whether a motor program will achieve its goal before it is carried out (thus, cerebellum)

–> accurately planning + controlling movement, where sensory consequences will signal how the movement turned out

BUT: activation of cerebellum decreases with practice showing reduction in error as skills improve

Question 24

Inverse model

Answer 24

Inverts the information flow of the forward model by putting the desired goal of the movement into action

–> calculates motor commands that are required

Question 25

Why can’t we tickle ourselves ?

Answer 25

Due to the sensory predictions made by the forward model

–> right anterior cerebellar cortex is selectively deactivated

e.g.: mediated by somatosensory + ACC

Question 26

Cerebellar ataxia

Answer 26

Results in jerky + imprecise movements

Question 27

Nystagmus

Answer 27

Difficulty of the eyes to maintain fixation

–> drifts from target then jumps back

Question 28

Golgi cells

Answer 28

1. Receives excitatory inout from parallel fibers
2. Gives inhibitory output to granule cells

–> modulation

Question 29

Is TMS a good method to treat cerebellar damages ?

Answer 29

Good method because non-invasive

–> stimulating m1 + cerebellar cortex