Cerebellum

Question 1

What is spinocerebellar ataxia?

Answer 1

Hereditary disease leading to cerebellar deterioration

Body movements become clumsy

Question 2

Give four elements of cerebellar ataxia

Answer 2

1. Hypotonia (weakness)
2. Dysmetria (inappropriate displacement, eg. over-reaching)
3. Dysdiadochokinesis (inability to make rapid alternating movement)
4. Decomposition of movement (lack of coordination of different joint movements)

Question 3

What is the output of the cerebellar cortex?

Answer 3

Purkinje cells

Question 4

What is the structure of Purkinje cells

Answer 4

Planar dendrites

Tree-like in sagittal plane

Narrow in coronal plane

Question 5

What do Purkinje cells do?

Answer 5

Project to and inhibit cells in cerebellar nuclei

GABAergic inhibition

Question 6

What is the largest cerebellar nucleus?

Answer 6

The dentate nucleus

Question 7

Where does the dentate nucleus project to?

Answer 7

Parts of thalamus that project to motor areas of cortex

Question 8

How many types of cell are in the cerebellar cortex?

Answer 8

5

Question 9

What are the granule cells?

Answer 9

The only excitatory neurons

Give rise to parallel fibres that excite Purkinje cells

Purkinje fibres can listen to approx 200,000 granule cells

Question 10

Give three features of the cerebellar cortex

Answer 10

1. Highly ordered
2. Uniform over whole cortex
3. Conserved between species

Question 11

What is the input to the cerebellum?

Answer 11

Mostly mossy fibres

Also climbing fibres

Question 12

Where do mossy fibres come from?

Answer 12

1. Some sensory fibres

2. Pons (cerebro-cerebellar relay)

Question 13

What do mossy fibres do?

Answer 13

Excite granule cells

Question 14

Where do climbing fibres come from?

Answer 14

Arise only from inferior olive in medulla

Question 15

What do climbing fibres do?

Answer 15

Causes Purkinje cell to discharge at least one action potential

Each Purkinje cell receives only one climbing fibre

Question 16

What controls brainstem descending motor pathways?

Answer 16

Vestibular and spinal cord inputs to cerebellum with output to brainstem motor pathways

Question 17

What controls motor cortex pathways?

Answer 17

Region of cerebellum that receives inputs from limb sensory pathways, the spinal cord and motor cortex with output to motor cortex

Question 18

What controls motor association cortex?

Answer 18

Extended region of lateral cerebellum that receives input from cerebral cortex (posterior parietal visual ‘where’) and particularly outputs to lateral premotor cortex

Question 19

How does the cerebellum learn?

Answer 19

Long term depression of parallel fibre pathways

Guided by climbing fibre signals

Subsequently learned pattern of activity in mossy fibres generates appropriate movement automatically

Question 20

What is the flocculus?

Answer 20

A region of the cerebellum

Involved in calibrating vestibulo-ocular reflex

Question 21

How does the flocculus mediate learning in vestibulo-ocular reflex?

Answer 21

1. Wrong amount of head movement
2. Retinal slip
3. Climbing fibre signals generated in flocculus
4. Mediates cerebellar plasticity in flocculus
5. Modifies output

Question 22

What is skeletomotor conditioning?

Answer 22

Sensorimotor associations learned by cerebellum

Climbing fibres are important instructive signals for cerebellar learning

Question 23

How do cerebellar lesions affect movement?

Answer 23

Coordination is severely impaired

Loss of motor learning - as if each movement is being done for the first time