The cerebellum and motor learning

Question 1

ROLE & ORGANISATION

i) give five roles of the cerebellum
ii) what is fed into the cerebellum?
iii) what signal can it produce? what does this allow?

Answer 1

i) maintainence of balance and posture
co-ord of voluntary movement
motor learning
cognitive function - interaction between different lobes
ensure instructions happen in the right order at the right time

ii) what you intend to happen as well as what is actually happening is fed in
iii) can produce a correction signal so next time you do the move better

Question 2

GROSS ANATOMY

i) name the three lobes
ii) what nuclei sits in the middle>
iii) what are the three cerebellar peduncles called? what do they allow?
iv) which structure seperates the two cerebellar hemispheres?

Answer 2

i) anterior, posterior anf flocculonodular lobe
ii) deep cerebellar nucleus sits in the middle
iii) sup, middle and inferior cerebellar peduncles allow communiation with the rest of the NS
iv) the vermis

Question 3

what is highligted in purple?

Answer 3

the deep cerebellar nucleus

Question 4

name the structures labelled A-F

name the structures labelled 1-3

Answer 4

A = anterior lobe
B = deep cerebellar nucleus 
C = cerebellar cortex
D = posterior lobe 
E = choroid plex of fourth ventricle
F = flocnodular lobe

1 = superior cerebellar peduncle
2 = middle cerebellar peduncle
3 = inferior cerebellar peduncle

Question 5

what areas are highlighted in

i) purple
ii) green
iii) orange

Answer 5

i) anterior lobe
ii) posterior lobe
iii) floculonodular lobe

Question 6

FUNCTIONAL SUBDIVISIONS

i) name the three key functional areas
ii) where do each of these areas bring information from and to?
iii) which areas do A - D correspond to?
iv) on a somatotopic map - which area corresponds to the trunk and which to the limbs?

Answer 6

i) vestibulocerebellum, spinocerebellum and cerebrocerebellum

ii) vestibulo from the vestibular organ to the flocnodular lobe, spino from the spinal cord to the vermis
cerebro from the cortex to either side of the vermis (hemispheres)

iii) A = spinocerebellum, B = cerebrocerebellum, C = vestibulocerebellum, D = vermis
iv) the trunk corresponds to the vermis and limbs correspond to the hemispheres

Question 7

LOBAR ANATOMY & NUCLEI

i) what are the three key loops of communication?
ii) what are the four key nuclei and where do they come from?

Answer 7

i) spino, vestibulo and cerebro
ii) four key nuclei are the fastigial (from vermis), interposed (from para-vermal area), vestibular and dentate (from hemis)

Question 8

which nuclei correspond to the

i) green
ii) blue
iii) red
iv) orange

areas of the cerebellum?

Answer 8

i) dentate
ii) interposted
iii) fastigial
iv) vestibular

Question 9

which nuclei output to descending spinal pathways?

which outputs to lateral desc pathway?

which outputs to the medial desc pathway?

Answer 9

fastigial and interposed output to the desc spinal pathways

interposed to lateral

fastigial to medial (FM)

Question 10

SPINOCEREBELLUM

i) what two things does it control?
ii) where is it anatomically located on the cerebellum?
iii) which two nuclei does this pathway input to?

Answer 10

i) controls muscle tone and posture
ii) anatomically it is located along each side of the vermis (where it recieves inputs from the spinal cord)
iii) inputs to the vermis then to the fastigial and interposed nuclei (which exit through the descending tracts)

Question 11

what loop is this?

explain the sequence of information from the cortex and back to the cortex?

Answer 11

cerebrocerebllar

cortex > pons > pontine nucleus > cerebellar hemis >dentate nucleus > feedback to the cortex via the thalamus

Question 12

i) what loop is this?
ii) explain the sequence from the vermis out
iii) give two effects of lesions in this pathway
iv) which drug may affect this pathway?

Answer 12

i) the spinocerebellar loop
ii) vermis > fastigial and interposed nuc > descending tracts
iii) lesions = gait ataxia (unsteady walking) and hypotonia (limb tone and posture disturbance)
iv) alcohol can disturb the vermis and cause unsteady gait

Question 13

CEREBELLAR PEDUNCLE PATHWAY

i) what are the three cerebellar peduncles?
ii) which two does the inflow come through?
iii) which one does the outflow go through
iv) which peduncle do pontine mossy fibres go through?
v) which peduncle do climbing fibres from the inferior olive and proprioceptive info from the spinocerebellar tract go through?

Answer 13

i) superior, middle and inferior
ii) inflow through middle and inferior
iii) outflow through superior
iv) pontine mossy fibres go through the middle
v) climbing fibres/proprioceptive info go through the inferior

Question 14

LESIONS IN THE CEREBROCEREBELLAR PATHWAY

name five consequences of lesions in this pathway and what happens when they occur
(movement, tremor, resp muscles)

Answer 14

1) dysmetria - movement is not stopped in time so there is overshoot (finger to nose test)
2) dysnergia - decomposition of complex movements - the body cant co-ordinate so movements arent smooth
3) dysdiadochokinesea - reduced ability to form rapidly alternating movements
4) intentional tremor - tremor arising when you go to perform a goal directed movement
5) dyarthria - poor co-ord of resp muscles, muscles of larynx causing uneven speech and velocity (corticocerebellar disruption)

Question 15

when does intentional tremor arise?

what makes it worse?

a lesion in which pathway causes it?

Answer 15

arises when you try to perform a goal directed movement

gets worse when you are moving towards a target

lesion in the cerebrocerebellar pathway causes it

Question 16

VESTIBULO-OCULAR PATHWAY

i) what is the role of this pathway
ii) which two nuclei do impulses pass to from the vestibular organ?
iii) what connects CN 6 (abducens) and CN 3 (oculomotor)
iv) what does disruption in this pathway cause? (2)

Answer 16

i) role of pathway is to excite one muscle and inhibit the opposing muscle to allow eye movement in a specific direction
ii) vestib organ > vestibular nucleus > abducens nucleus
iii) the medial longitudinal fasiculus connects CN6 and CN3

iv) disruption/lesion to this pathway causes nystagmus (invol/rhythmical and repeated oscillations in one or both eyes)
- also causes fuzzy vision

Question 17

a lesion in which pathway causes this?

Answer 17

vestibulocerebellar

Question 18

a lesion in which pathway causes this posture?

Answer 18

spinocerebellar

Question 19

CEREBELLAR CIRCUITRY

i) which peduncle do mossy and climbing fibres travel through?
ii) what information do mossy fibres carry and where does this info come from?
iii) where do climbing fibres originate?
iv) after outputting to the deep cerebellar nuclei - which three structures does information pass to?

Answer 19

i) inferior peduncle
ii) mossy fibres carry proprioceptive information and it comes from the spinocerebellar tract
iii) climbing fibres originate from the inferior olive in the medulla
iv) output from cerebellum to deep cerebellar nuclei to the thalamus, red nucleus and vestibular nucleus

Question 20

CEREBELLAR CORTEX STRUCTURE

I) which fibres does the molecular layer contain? which cells do these fibres come from?

ii) where does the purkinje cell layer output to?
iii) which fibres fire out instructions about what you want to do?
iv) which fibres from the inferior olive generate error signals?

Answer 20

i) molec layer contains parallel fibres that come from granule cells
ii) purkinje cell layer outputs to the deep cerebellar nuclei
iii) mossy fibres fire out instructions about what you want to do
iv) climbing fibres generate error signals if you dont do the intended movement

Question 21

which fibres are represented by A and B?

Answer 21

A = mossy fibres

B = climbing fibres

Question 22

What are labels A, B and C?

Answer 22

A = parallel fibre

B = purkinje cell

C = granule cell

Question 23

what mechanism allows the brain to learn and correct previous mistakes?

Answer 23

long term depression

Question 24

LONG TERM DEPRESSION & MOTOR LEARNING

i) what does this give the brain the ability to do?
ii) which two fibre pathways does this involve? what happens when they are activated at the same time? explain this
iii) which ion is this mediated by and what effect does it have on AMPA receptors?

Answer 24

i) gives the brain the ability to learn and correct previous mistakes

ii) involves climbing fibre and mossy fibre pathways
- intention (sensory motor signals) are sent from the mossy fibres > gran cell > parallel > purkinje
- climbing fibres receive input of whats happening and if this is not the intention then an error signal is generated
- the error signal then passes out via the climbing fibres

** when the climbing fibres (error signal) and mossy fibres stimulate the purkinje cell at the same time - the synapse is weakened and this causes LTD** (as movement is paired with an error signal)

iii) mediated by calcium and causes internalisation of AMPA receptors

Question 25

CAUSES OF CEREBELLAR DYSFUNCTION

i) give four examples of genetic causes and define each one
ii) give five examples of acquired causes
iii) which area of the cerebellum can alcohol cause degeneration of? what symptoms would this cause?

Answer 25

i) genetic causes
1) frederichs ataxia - disorder of co-ord, balance and speech
2) spinocerebellar degeneration - ataxia can occur if major connections are disrupted
3) ataxia telengiectasia - see caps on skin and bruise easily
4) Von hippel lindau - tumours such as haemangioblastoma

ii) acquired causes
1) alcohol - cerebellar atrophy
2) metabolic - B12, coeliac, thyroid
3) drugs - anti epileptics such as phenytoin
4) degenerative - multiple system atrophy
5) immune
6) antibodies from a tumour - attack cells in the molecular layer that cause cerebellar ataxia

iii) alcohol can cause degeneration of the anterior (spino) cerebellum (other regions will still be in tact) which causes difficulty with walking but little impairment in arm movement or speech

Question 26

FOCAL CEREBELLAR PATHOLOGY

i) damage to which three areas is most likely to cause ataxia? why is this?
ii) what happens if you get inflammation or a lesion in the peduncle area?
iii) what is most important - lesion location or lesion size?

Answer 26

i) damage to cerebellar nuclei, brainstem nuclei or white matter tracts are most likely to cause ataxia (not cerebellar cortex as this has some degree of plasticity)
ii) inflammation or a lesion in the peduncle area is catastrophic
iii) lesion location is more important than lesion size