The Cerebellum

Question 1

Where is the cerebellum located?

Answer 1

Located at the back of the brain under the occipital lobe, level with the brain stem.

Question 2

Cerebellar stats

Answer 2

Comprises only 10-20% of the brains volume but contains more than 50% of its neurons.

Question 3

Outline the structural organisation of the cerebellum.

Answer 3

Highly ordered structure with densely packed neurons and a repeating modular arrangement.

Question 4

Name the 3 layers of the cerebellar cortex from outermost to innermost.

Answer 4

Molecular layer
Purkinje layer
Granule cell layer

Question 5

Describe the structure of the folia.

Answer 5

Consist of outer grey matter (cerebellar cortex) as well as inner white matter that contains the deep nuclei.

Question 6

Name the output nuclei of the cerebellum.

Answer 6

The deep nuclei

Question 7

Contents of the molecular layer of the cerebellar cortex.

Answer 7

Granule cell axons (parallel fibres)
Stellate and basket cells
Purkinje dendritic tree

Question 8

Contents of the Purkinje layer of the cerebellar cortex.

Answer 8

Purkinje cell bodies

Question 9

Contents of the granule cell layer of the cerebellar cortex.

Answer 9

Granule cell bodies
Golgi cells
Cerebellar glomeruli where granule cells connect to mossy fibres

Question 10

Name the 5 types of cell found in the cerebellar cortex.

Answer 10

Stellate cells
Basket cells
Golgi cells
Purkinje cells
Granule cells

Question 11

What are the 2 inputs to the cerebellar cortex?

Answer 11

Climbing fibres and mossy fibres.

Question 12

Does the cerebellum influence movement of the contralateral or ipsilateral side of the body, and does this involve any crossing over?

Answer 12

Ipsilateral body meaning there is no crossing over.

Question 13

Name the three lobes of the cerebellum divided by the transverse fissures.

Answer 13

Anterior, posterior and flocculonodular lobe.

Question 14

Name the three lobes of the cerebellum divided by the longitudinal fissures.

Answer 14

Vermis, intermediate and lateral zones / lobes.

Question 15

Which circuit (direct or indirect) increases cerebellar output?

Answer 15

The DIRECT circuit.

Question 16

Which circuit (direct or indirect) decreases cerebellar output?

Answer 16

The INDIRECT circuit.

Question 17

Describe disinhibition (with example from cerebellar circuitry)

Answer 17

The inhibition of an inhibitory neuron eg. excitation of stellate and basket cells via excitatory input from parallel fibres. Leads to an increase in stellate / basket cells’ inhibition of the purkinje cells, decreasing PKJ cell activity.

Question 18

Briefly define feedback inhibition

Answer 18

Inhibition of the input - when an inhibitory cell inhibits the excitatory cell from which it normally receives input.
When (excitatory) cell A activates (inhibitory) cell B, resulting in cell B inhibiting cell A (ie. when a cell inhibits the cell it normally receives input from).

Question 19

Briefly define feedforward inhibition.

Answer 19

Inhibition of the final output.

Question 20

Describe an example of feedback inhibition found in the cerebellum.

Answer 20

When activated, the parallel fibres (granule cell axons) excite PKJ cells. They also excite golgi cells which in turn feedback to inhibit the granule cells (ie. cells from which they had initially received input).

Question 21

Describe an example of feedforward inhibition found in the cerebellum.

Answer 21

When activated, the parallel fibres (granule cell axons) excite PKJ cells. They also excite stellate and basket cells which in turn inhibit the activity of the recently activated PKJ cells.

Question 22

Describe the effects of the general network mechanism known as feedback inhibition.

Answer 22

Elicits complex activity patterns (in PKJ cells) including rhythmic oscillatory activity.

Question 23

Describe the effects of the general network mechanism known as feedforward inhibition.

Answer 23

Sets up a brief window of activity (in the PKJ cell) that is quickly shut down.

Question 24

Where do climbing fibres originate from?

Answer 24

The inferior olive.

Question 25

What cells do climbing fibres connect to in the cerebellar cortex?

Answer 25

Purkinje cells.

Question 26

Describe the type of connection make btw climbing fibres and PKJ cells.

Answer 26

1 climbing fibre synapses onto 1 PKJ through wrapping around it’s cell body and dendrites.
Each single climbing fibre makes multiple connections with the single PKJ (no convergence or divergence).
Extremely powerful input called a ‘complex spike’

Question 27

Describe the complex spike that occurs btw PKJ and climbing fibres.

Answer 27

A single AP in a climbing fibre elicits a large excitatory synaptic potential in the PKJ, resulting in a burst of APs.

Question 28

What cells do the mossy fibres connect to in the cerebellar cortex?

Answer 28

Granule cells.

Question 28

Describe the type of connection that occurs btw mossy fibres and granule cells.

Answer 28

The summed activity in mossy fibres triggers a single AP, a ‘simple spike’

Question 29

Describe the connections btw parallel fibres and PKJ cells.

Answer 29

A single PKJ cell receives input from roughly 250,000 granule cells - convergence of parallel fibres.

Question 30

Describe the structure of the purkinje cells.

Answer 30

Have a large fan-like dendritic tree that extends into the molecular layer, but only in one plane.