Lecture 8: Supraspinal Motor Control - Cerebellum

Question 1

If someone obtains an injury that damages their cerebellum, would they have sensory loss or motor loss?

Answer 1

Motor loss.

Question 2

If someone has a lesion in their cerebellum, can they re-learn movements? What does this imply about it’s function?

Answer 2

No. This implies that the cerebellum is involved in the preplanning of movement.

Question 3

Does the cerebellum play a role in coordination of movement?

Answer 3

Yes.

Question 4

The cortical layer of the dorsal surface of the cerebellum is repeatedly folded into a series of transverse ridges, what are these called?

Answer 4

Folia.

Question 5

What is the purpose of the folia?

Answer 5

To increase surface area of the cerebellar cortex.

Question 6

The cerebellum contains less than 50% of the total CNS neurons, true or false?

Answer 6

False! Even though the cerebellum constitutes only 10% of total brain volume, it contains more than 50% of the total CNS neurons.

Question 7

What is the “spine-like” structure of the cerebellum called?

Answer 7

Vermis.

Question 8

What separates the anterior lobes from the posterior lobes of the cerebellum?

Answer 8

The primary fissure.

Question 9

Which lobes of the cerebellum does the posterior fissure separate?

Answer 9

The posterior lobe and the flocculonodular lobe.

Question 10

The spinocerebellum contains which structures?

Answer 10

The vermis and the paravermis.

Question 11

What is the function of the spinocerebellum?

Answer 11

Controls body and limb movement.

Question 12

The cerebrocerebellum is made up of which structures?

Answer 12

Both hemispheres of the cerebellum.

Question 13

The vestibulocerebellum is made up of which lobe?

Answer 13

The flocculonodular lobe.

Question 14

Which lobe of the cerebellum is responsible for controlling eye movements?

Answer 14

Flocculonodular lobe

Question 15

Where are the deep cerebellar nuclei located in the cerebellum?

Answer 15

Deep within the white matter of the cerebellum.

Question 16

Where do deep cerebellar nuclei relay cerebellar cortical output to?

Answer 16

The Brainstem.

Question 17

Which cell dendrites extend into the outer molecular layer?

Answer 17

Purkinje cell dendrites.

Question 18

What are deep cerebellar nuclei?

Answer 18

Clusters of neurons deep within the white matter of the cerebellum.

Question 19

What do Purkinje cell axons synapse onto?

Answer 19

Neurons within deep cerebellar nuclei.

Question 20

Are Purkinje cells excitatory or inhibitory? What neurotransmitter do they use?

Answer 20

Inhibitory. GABA.

Question 21

Purkinje cells receive an input from which fibres?

Answer 21

Climbing fibres.

Question 22

Where do climbing fibres arise from?

Answer 22

Inferior olive in the brain stem.

Question 23

What does the inferior olive integrate information from?

Answer 23

Muscle proprioceptors.

Question 24

Each Purkinje cell receives input from how many inferior olive cells?

Answer 24

One. Each Purkinje cell receives input from one inferior olive cell. But a single climbing fibre makes hundreds of excitatory synapses with Purkinje dendrites.

Question 25

Pontine nuclei in the Brainstem relay information to the cerebellum from where?

Answer 25

The cerebral cortex.

Question 26

Where do Mossy fibres arise from?

Answer 26

Pontine nuclei in the Brainstem.

Question 27

Which cells do mossy fibres synapse onto?

Answer 27

Granule cells.

Question 28

Which cells have axons that ascend to the molecular layer and branch at a right angle creating parallel fibres?

Answer 28

Granule cells.

Question 29

Do Purkinje cells receive input from many or few parallel fibres?

Answer 29

Very many!

Question 30

Explain why the cerebellum is thought to act as a comparator.

Answer 30

- feedback mechanisms are too slow to control motor output - it is thought that when a motor command is given, an “efference copy” is also made which is a guess of sensory consequences of a command. - the guesses can therefore be modified by discrepancies between sensory feedback and predicted feedback.

Question 31

What is the vestibulo-occular reflex (VOR)?

Answer 31

A reflex that produces eye movements in the opposite direction to head movement, which stabilises vision relative to space.

Question 32

How does the cerebellum adjust the vestibulo-occular reflex?

Answer 32

Vestibular Mossy fibres signal the granular cells which in turn activate Purkinje cells through their parallel fibres. The Purkinje cells then transmit this information to the vestibular nuclei that informs the oculomotor nuclei which then controls the eye movements. Eye signals inferior olive which then activate Purkinje cells through climbing fibres signalling a “retinal slip”, an error signal.

Question 33

Do parallel fibres influence climbing fibre input to Purkinje cells or do climbing fibres influence parallel fibre input to Purkinje cells? What is the significance of this?

Answer 33

Climbing fibres influence parallel fibre input to Purkinje cells. The climbing fibres teach Purkinje cells which parallel fibres are important so that the cerebellum “learns” which outputs are important in a particular movement context. This enables the cerebellum to automate commands from the cerebral cortex.