Cerebellum

Question 1

Components of the basal ganglia, thalamus and brainstem

Answer 1

• 0.7 billion neurons
• 7.8% of brain mass
• 0.8% of total brain neurons

Question 2

Components of the cerebral cortex

Answer 2

• 16 billion neurons
• 81.2% of brain mass
• 19% of total brain neurons

Question 3

Components of the cerebellum

Answer 3

• 69 billion neurons
• 10.3% of brain mass
• 80.2% of total brain neurons

Question 4

Cerebellum rule of 3

Answer 4

• 3 lobes (anterior, posterior, Flocculonodular)
• 3 functional subdivisions
• 3 pairs of peduncles
• 3 pairs of nuceli
• 3 corticol layers

Question 5

What is the function of the cerebellum

Answer 5

• movement and coordination
• maintenance of posture
• maintenance of muscle tone/balance
• motor learning

Question 6

Where is the cerebellum

Answer 6

• situated posterior of the brainstem
• cerebellum integrates sensory inputs and motor outputs making it an ideal location for motor learning
• cerebellum constitutes only 10% of total brain volume but contains >80% of its neurons

Question 7

consequences of cerebellar damage

Answer 7

• cerebellar does not result in complete movement abolition, but does cause severe movement disruption
• ataxia is the abnormal execution of multi jointed voluntary movements, characterised by lack of coordination
• cerebellar ataxia is caused by stroke, multiple sclerosis, tumour etc

Question 8

gross anatomy of the cerebellum

Answer 8

• cerebellar peduncles
  
  • superior
  • middle
  • inferior
• cerebellar cortex
  
  • cerebrocerebellum
  • spinocerebellum
  • vestibulocerebellum
• deep cerebullar nuclei
  
  • dentate nucleus
  • interposed nucleus
  • fastigial nucleus

Question 9

cerebellar peduncles

Answer 9

• superior peduncle
  
  • no inputs
  • outputs to motor cortex (via thalamus) and red nucleus
• middle peduncle
  
  • inputs from motor cortex (via pons)
  • no outputs
• inferior peduncle
  
  • inputs from inferior olivary nucleus, spinal cord and vestibular nuceli
  • outputs to reticular formation (brainstem), spinal cord and vestibular nuclei

Question 10

cerebellar cortex

Answer 10

• split into 3 functional subdivisions
  
  • cerebrocerebellum
  • spinocerebellum
  • vestibulocerebellum
• the cerebellar cortex contains highly sophisticated neural circuitry that integrates inputs from the cortex, brainstem and spinal cord and modulates motor outputs

Question 11

cerebrocerebellum

Answer 11

• largest region of the cerebellar cortex
  
  • projects to and from cerebral (motor) cortex
  • involved in motor planning
• input(s)
  
  • pons, from motor cortex (via thalamus)
  • inferior olive, from motor cortex (via red nucleus) and spinal cord
• output(s)
  
  • denate nucleus, to motor cortex (via thalamus)

Question 12

spinocerebellum

Answer 12

• comprises the vermis and intermediate cortex
• regulates body and limb movements
• somatic sensory inputs exhibit somatotopy
  
  • vermis = trunk and head
  • intermediate cortex = limbs
• input(s)
  
  • vermis
    
    • spinal cord, carrying sensory information from the trunk and head
  • intermediate cortex
    
    • spinal cord carrying sensory information from the limbs
• output(s)
  
  • vermis
    
    • fastigial nucleus to medial descending reticulospinal and vestibulospinal tracts
    • motor execution
  • immediate cortex
    
    • interposed nucleus to lateral descending corticospinal and rubrospinal tracts
    • motor planning

Question 13

vestibulocerebellum

Answer 13

• also known as the flocculonodular lobe
  
  • oldest evolutionary part of the cerebellum
  • only region of the cerebellar cortex to bypass the deep cerebellar nuclei
  • regulates balance and eye movements
• input(s)
  
  • vestibular nucleus, from semicircular canals and otolith organs
• output(s)
  
  • vestibular nucleus, to axial and proximal muscles, limb extensors, and head/eye muscles

Question 14

Deep cerebellar nuclei

Answer 14

• denate
  
  • most lateral nucleus
  • located in the 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
• fastigial
  
  • most medial nucleus
  • located in vermis (spinocerebellum)
  • output is reticular formation and vestibular nucleus via inferior peduncle

Question 15

cerebellar cortex: inputs

Answer 15

receives inputs from pontine nuclei, inferior olive (climbing fibres only), spinal cord and vestibular nuclei

Question 16

cerebellar cortex: outputs

Answer 16

• cerebrocerebellum
  
  • denate nucleus -> motor cortex
  • motor planning
• spinocerebellum
  
  • fastigial 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 17

cerebellar circuitry

Answer 17

• the cerebellar neural circuitry is highly sophisticated
• the principle elements are:
  
  • mossy fibres (granule layer)
  • granule cells (granule layer)
  • climbing fibres (granule layer)
  • purkinje cells (purkinje cell layer)
  • parallel fibres (molecular layer)

Question 18

Purkinje cells

Answer 18

• consists of a cell body and a vast dendritic tree
  
  • each purkinje cell has about 200,000 synapses with parallel fibres crossing its dendritic tree
  • the dendrites receive afferent input from parallel fibres and the climbing tree
  • surface area covers 2 front doors
  • out output to the deep cerebellar nuclei
  • exclusive cerebellar output is via purkinje cells
  • 40:1 ratio of input to output
• function is inhibitory

Question 19

cerebellar circuitry

Answer 19

• mossy fibres are the primary neurons 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 outputs
• unlike mossy fibres, there is only one climbing fibre
  
  • the climbing fibres excites purkinje cells directly (but can also inhibit via interneurons)
  • originates in the inferior olive
  • believed to sense error signals to elicit learning

Question 20

conditioned eye blink response

Answer 20

• the conditioned eye blink response is an example of cerebellar sensorimotor learning
• a neutral 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 (pavlovs dog)

Question 21

Marr-Albus-Ito hypothesis

Answer 21

• the mechanism underpinning conditioned the eye blink blink response is thought to reflect the Marr-Albus-Ito hypothesis of leaning
• 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 (LTD)
• because purkinje cells are inhibitory, LTD increases the output of deep cerebellar nuclei