Cerebellum (wk 5)

Question 1

What is contained in the cerebellum?

Answer 1

-The cerebellum contains: 3 lobes (anterior, posterior, flocculonodular), 3 functioal subdivisions, 3 pairs of peduncles, 3 pairs od deep nuclei, 3 cortical layers

Question 2

What are the functions of the cerebellum?

Answer 2

-> Cerebellum constitutes only 10% of total brain volume but contains >80% of its neurons. Situated posterior of the brainstem. Primary functions are: Movement coordination, Maintenance of posture, Maintenance of muscle tone/balance and Motor learning. The cerebellum integrates sensory inputs and motor outputs making it an ideal location for motor learning.

Question 3

What are the consequences of cerebellar damage?

Answer 3

-> Cerebella damage does not result in complete movement abolition, but does cause severe movement disruption. Ataxia is the abnormal execution of multi-joined voluntary movements, characterized by lack of coordination. Cerebellar ataxia is caused by stroke, multiple sclerosis, tumour etc.

Question 4

What are the 3 major components of the cerebellum?

Answer 4

1. Cerebellar peduncles -> superior, middle, inferior
2. Cerebellar cortex -> cerebrocerebellum, spinocerebellum, vestibulocerebellum
3. Deep cerebellar nuclei -> denate nucleus, interposed nucleus, fastigal nucleus

Question 5

What are the 3 functional subdivisions of the cerebellar cortex?

Answer 5

Cerebrocerebellum, Spinocerebellum, Vestibulocerebellum

Question 6

Describe the Cerebrocerebellum

Answer 6

-> Largest region of the cerebellar cortex. Projects to and from cerebral (motor) cortex. Involved in motor planning. Inputs: Pons, from motor cortex (via thalamus) and Inferior olive, from motor cortex (via red nucleus) and spinal cord. Ouputs: Dentate nucleus, to motor cortex (via thalamus)

Question 7

Describe the Spinocerebellum?

Answer 7

-> Comprises the vermis and intermediate cortex. Regulates body and limb movements. Somatic sensory inputs exhibit somatotopy – Vermis= trunk and head and Intermediate cortex= limbs. Inputs: Vermis (spinal cord) and Intermediate cortex (spinal cord). Outputs: Vermis (Fastigal nucleus to medial descending reticulospinal and vestibulospinal tract) for motor execution and Intermediate cortex (Interposed nucleus to lateral descending corticospinal and rubrospinal tract) for motor planning.

Question 8

Describe the Vestibulocerebellum?

Answer 8

-> Known as the flocculondular lobe. Oldest evolutionary part of cerebellum. Only region of the cerebellar cortex to bypass the deep cerebellar nuclei. Regulates balance and eye movements. Input: Vestibular nucleus, from semicircular canals and otolith organs. Output: Vestibular nucleus, to axial and proximal muscles, limb extensors, and head/eye muscles.

Question 9

Describe the cerebellar cortex:

Answer 9

-The cerebellar cortex contains highly sophisticated neural circuitry that integrates input from the cortex, brainstem and spinal cord and modulates motor outputs

Question 10

Describe the 3 cerebellar peduncles:
-Super, middle, inferior

Answer 10

-The cerebellum is connected to the dorsal aspect of the brainstem by 3 symmetrical pair of peduncles:
1. Superior peduncle -> No inputs, outputs to the motor cortex (via thalamus) and red nucleus
2. Middle peduncle -> Input from motor cortex (via pons), no outputs
3. Inferior peduncle -> Inputs from inferior olivary nucleus, spinal cord and vestibular nuclei and Outputs to reticular formation (brainstem), spinal cord and vestibular nuclei.

Question 11

Describe the deep cerebellar nuclei
-Denate, interposed, fastigal

Answer 11

-Denate -> Most lateral nucleus. Located in cerebrocerebellum. Output is to motor cortex via superior peduncle and thalamus.
-Interposed -> Located in intermediate cortex (spinocerebellum). Output is to red nucleus via superior peduncle.
-Fastigal -> Most medial nucleus. Located in vermis (spinocerebellum). Output is to reticular formation and vestibular nucleus via inferior peduncle.

Question 12

What are the inputs of the cerebellum?

Answer 12

-> Pontine nuclei, inferior olive (climbing fibres only), spinal cord, and vestibular nuclei

Question 13

What are the outputs of the cerebellum?

Answer 13

• Cerebrocerebellum -> Denate nucleus, motor cortex motor planning
• Spinocerebellum -> Fastigal nucleus (vermis) – reticular formation and vestibular nucleus. Interposed nucleus (intermediate cortex) – red nucleus. Motor execution.
  Vestibulocerebellum -> Vestibular nucleus – spinal cord. Balance and eye movements

Question 14

What is the cerebellar circuitry and the 5 principle elements:

Answer 14

-Cerebellar circuitry -> The cerebellar neural circuitry is highly sophisticated. The principle elements are:
* Mossy fibres (granule layer)
* Granule cells (granule layer)
* Climbing fibres (granule layer)
* Purkinje fibres (Purkinje cell layer)
* Parallel lines (molecular layer)

Question 15

Describe Purkinje cells:

Answer 15

-Purkinje cells -> Consists of a cell body and a vast dendritic tree:
1. Each cell has about 200,000 synapses with parallel fibres crossing its dendritic tree
2. The dendrites receive afferent input from parallel fibres and the climbing fibre
3. Surface area covers 2 front doors
4. One output to the deep cerebellar nuclei
5. Exclusive cerebellar output is via Purkinje cells
6. 40:1 ratio of input to output
7. Function is inhibitory

Question 16

Describe the 4 steps in the cerebellar circuitry system:

Answer 16

• Mossy fibres are the primary neurones that carry information into the cerebellum -> activate granule cells and cerebellar nuclei
• Granule cells attach to parallel fibres which synapse with dendrites of Purkinje cells
• Once activated, Purkinje cells inhibit cerebellar nuclei, modulating motor output
• Unlike mossy fibres, there is only one climbing fibre. The climbing fibre excites Purkinje cells directly. Originate in the inferior olive. Believed to sense error signals to elicit learning.

Question 17

Describe the conditioned eye-blink response:

Answer 17

• The response is an example of cerebellar sensorimotor learning.
• A neural stimulus, known as the conditioned stimulus (CS), is paired with an aversive stimulus, known as the unconditioned stimulus (US)
• The US elicits a reflex response known as the unconditioned response (UR)
• After a sufficient number of paired associations, the CS now elicits a conditioned response (CR) that attenuates the UR
• This is a form of classical conditioning (Pavolv’s dogs)

Question 18

What is the Marr-Albus-Ito hypothesis?

Answer 18

-> Known as Marr-Albus-Ito hypothesis of associative learning. Simultaneous activation of climbing fibres (the teacher) and mossy fibres (the learner) causes long term changes (i.e. plasticity) in parallel fibre to Purkinje cell synapses, resulting in long term depression. Because Purkinje cells are inhibitory, long term depression increases the output of deep cerebellar nuclei.