Cerebellum Flashcards
What is spinocerebellar ataxia?
Hereditary disease leading to cerebellar deterioration
Body movements become clumsy
Give four elements of cerebellar ataxia
- Hypotonia (weakness)
- Dysmetria (inappropriate displacement, eg. over-reaching)
- Dysdiadochokinesis (inability to make rapid alternating movement)
- Decomposition of movement (lack of coordination of different joint movements)
What is the output of the cerebellar cortex?
Purkinje cells
What is the structure of Purkinje cells
Planar dendrites
Tree-like in sagittal plane
Narrow in coronal plane
What do Purkinje cells do?
Project to and inhibit cells in cerebellar nuclei
GABAergic inhibition
What is the largest cerebellar nucleus?
The dentate nucleus
Where does the dentate nucleus project to?
Parts of thalamus that project to motor areas of cortex
How many types of cell are in the cerebellar cortex?
5
What are the granule cells?
The only excitatory neurons
Give rise to parallel fibres that excite Purkinje cells
Purkinje fibres can listen to approx 200,000 granule cells
Give three features of the cerebellar cortex
- Highly ordered
- Uniform over whole cortex
- Conserved between species
What is the input to the cerebellum?
Mostly mossy fibres
Also climbing fibres
Where do mossy fibres come from?
- Some sensory fibres
2. Pons (cerebro-cerebellar relay)
What do mossy fibres do?
Excite granule cells
Where do climbing fibres come from?
Arise only from inferior olive in medulla
What do climbing fibres do?
Causes Purkinje cell to discharge at least one action potential
Each Purkinje cell receives only one climbing fibre
What controls brainstem descending motor pathways?
Vestibular and spinal cord inputs to cerebellum with output to brainstem motor pathways
What controls motor cortex pathways?
Region of cerebellum that receives inputs from limb sensory pathways, the spinal cord and motor cortex with output to motor cortex
What controls motor association cortex?
Extended region of lateral cerebellum that receives input from cerebral cortex (posterior parietal visual ‘where’) and particularly outputs to lateral premotor cortex
How does the cerebellum learn?
Long term depression of parallel fibre pathways
Guided by climbing fibre signals
Subsequently learned pattern of activity in mossy fibres generates appropriate movement automatically
What is the flocculus?
A region of the cerebellum
Involved in calibrating vestibulo-ocular reflex
How does the flocculus mediate learning in vestibulo-ocular reflex?
- Wrong amount of head movement
- Retinal slip
- Climbing fibre signals generated in flocculus
- Mediates cerebellar plasticity in flocculus
- Modifies output
What is skeletomotor conditioning?
Sensorimotor associations learned by cerebellum
Climbing fibres are important instructive signals for cerebellar learning
How do cerebellar lesions affect movement?
Coordination is severely impaired
Loss of motor learning - as if each movement is being done for the first time
