2.10 Cerebellum

Question 1

Give an introductory description to the cerebellum

Answer 1

The cerebellum is known as the little brain and is located at the back of the brain, behind the brainstem. It makes up 11% of total brain weight. It has sensorimotor, cognitive and affective functions. The cerebellum is very complex and different regions correlate to different functional outputs.

Question 2

Describe the gross structure of the cerebellum.

Answer 2

The primary fissure separates the anterior and posterior lobes of the cerebellum. The superior vermis acts as the ‘spine’ of the cerebellum which separates its two hemispheres. The superior, middle and inferior peduncles connect to the pons to anchor the cerebellum. The flocculus and nodule combine to form the flocculonodular lobe which is at the bottom tucked up underneath the cerebellum.

Question 3

What mechanisms increase the surface area of the cerebellum

Answer 3

The cerebellum has lots of folds called folia to increase the surface area. Additionally, there are deep transverse fissure which divides the cerebellum into 10 lobules, this also increases the surface area.

Question 4

What are the functional areas of the cerebellum

Answer 4

-vestibulocerebllum is the function definition in the area of the flocculonodular lobe which sends outputs directly to the vestibular nueclei, helping with balance, eye movements and vestibulo-ocular reflex

-the spinocerebellum is the functional definition in the area of vermis and paravermis, it receives visual, auditory, vestibular and sensorimotor inputs, helping with tone, posture and movement

-the cerebrocerebellum is the functional definition in the lateral hemisphere areas, it recieves and sends info to the cortex, helping with volitional movement, motor planning and cognitive tasks

However, he areas and functions are not quite clean cut and corresponding, they exist interconnectedly.

Question 5

What is the cerebellar cortex

Answer 5

The outer layer of the cerebrum

Question 6

What are the 3 layers in the cerebellar cortex

Answer 6

molecular cell layer, purkinje cell layer and granular cell layer

Question 7

What is below the cerebellar cortex

Answer 7

White matter

Question 8

Describe the molecular cell layer of the cerebellar cortex

Answer 8

The superficial layer which is a synaptic zone made up of branching dendrites of purkinje cells (which project from the purkinje layer to the molecular layer) and axons of granule layers (also has basket cells)

Question 9

Describe the purkinje cell layer of the cerebellar cortex

Answer 9

A single row of the purkinje cell bodies (with the dendrites projecting into the molecular layer) - purkinje cell axons project to deep cerebellar nuclei, the purkinje cells receive input from climbing fibres and mossy fibres (via granule cell)

Question 10

Describe the granule cell layer of the cerebellar cortex

Answer 10

The deepest layer, closely packed interneurons particularly granule cells along with brush and golgi cells

Question 11

What are purkinje cells

Answer 11

Purkinje cells have lots of extending dendritic branches and are very recognisable, the purkinje cell axons project into deep cerebellar nuclei

Question 12

What receives signals from purkinje cells

Answer 12

Deep cerebellar nuclei which are clusters of neurones deep within white matter of cerebellum that recieve info from purkinje and relay the cerebellar cortical output to the brainstem

Question 13

Describe the 2 inputs into purkinje cells

Answer 13

the 2 inputs to purkinje cells are climbing fibres and mossy fibres

input to the purkinje cells comes from inferior olive cells (which are intergrating info from muscle proprioceptors), the inferior olive projects climbing fibres which form many synapses with the dendritic branches of purkinje cells

input to the purkinje cells also comes from pontine nuclei (in the pons), these inputs are called mossy fibres which project onto granule cells, each axon of a granule cell splits and travels in a parallel direction and synapses with many purkinje cells

Question 14

What is one difference between climbing fibres and mossy fibres

Answer 14

The mossy fibres project onto granule cells which can synapse with many purkinje cells, however climbing fibres can only synapse with one purkinje cell (but multiple dendrites within it)

Question 15

What cells synapse granule cells to purkinje cells

Answer 15

Basket cells, they are scattered in the molecular layer

Question 16

What are 2 cells with modulatory roles in the circuitry of the cerebellum

Answer 16

stellate cells and golgi cells

Question 17

Describe how the cerebellum functions as a comparator

Answer 17

Feed back mechanisms to a movement are too slow, so the the cerebellum gives a feed forward mechanism to predict the sensory consequences of a motor movement (efference copy), the brain then compares the difference between its prediction and the actual sensory response, allows for the brain to refine and learn how to perform actual motor tasks. This he predictive guess of sensory consequences of a motor command is called an efference copy, he cerebrum then acts as a comparator of the two copies.

Question 18

Describe the role of the cerebrum in the vestibulo-occular reflex

Answer 18

If the head is moving, sensory signals from vestibular apparatus are modified by input from cerebellum, this allows image received to remain stable on the retina despite head moving, the reflex produces eye movements in the opposite direction to the head movement which stabilises the vision.