TASK 3 - CEREBELLUM Flashcards Preview

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Flashcards in TASK 3 - CEREBELLUM Deck (31):
1

cerebellum

- located in hindbrain
- metencephalon (cerebellum + pons)
- played critical role in development of cortical/ cognitive functions
- allows info input into and out of cerebellum
--> input via brainstem into cerebellum
--> output via pons out of cerebellum --> into cortex

2

structural divisions

- laminated cerebellar cortex on surface
- cerebellar deep nuclei deep in white matter

3

structural divisions
- lobes

- anterior lobe: somatosensory info
- posterior lobe: output to cortex
- flocculonodular lobe: oldest cerebellar structure

4

structural divisions
- vermis + hemispheres

- vermis: runs along midline of cerebellum, separates 2 hemispheres

5

functional divisions
1. cerebrocerebellum

= lateral hemispheres
- receives input from the CEREBRUM
- planning, initiation of movement + sensory feedback of motor movements
- coordination of voluntary movements
- cognitive, emotional control

6

functional divisions
2. spinocerebellum

= vermis
- input from SPINAL cord
- visual + auditory signals (relayed in brainstem nuclei)
- regulates body + limb movements and muscle tone
- compares info from where body stand and where it should be --> if discrepancy: corrects error signal

7

functional divisions
3. vestibulocerebellum

= floculonodular/flocular lobe
- input from VESTIBULAR complex
- regulates balance, posture, eye movements

8

pathways

1. via cerebellar peduncles
2. via deep cerebellar nuclei

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pathways
1. cerebellar peduncles

= white matter connections
- connections between the cerebellum and other parts of the nervous system
- contain fine branching nerve fibres

10

1. cerebellar peduncles
a) superior

= largest output structure/ almost entirely efferent pathway
- origin: deep cerebellar nuclei neurones --> to upper motor neurones in deep layers of superior colliculus --> delay in dorsal thalamus --> primary motor, premotor areas of cortex
- limbic movements

11

1. cerebellar peduncles
b) middle

= biggest peduncle; afferent pathway to cerebellum; descending
- origin: pontine nuclei (neurones in the base of the contralateral pons) --> receives input from many sources (almost all cortical areas and superior colliculus) --> axons (transverse pontine fibres) cross midline and enter cerebellum via middle cerebellar peduncle
- regulates info from proprioception (orient body in space) + regulates other sensory functioning

12

1. cerebellar peduncles
c) inferior

= smallest but most complex peduncle
- contains afferent + efferent pathways
1) afferent ascending = axons from vestibular nuclei, spinal cord and brainstem tegmentum (inferior olive)
2) efferent = axons project to vestibular nuclei and reticular formation
- proprioceptive info (how different body parts relate to one another

13

pathways
2. deep cerebellar nuclei

= in each cerebellar hemisphere there are 4 major deep nuclei
- each receiving input from different parts of cerebellum
a) fastigal nuclei
b) interposed nuclei (x2)
c) dentate nuclei

14

input

- major destination of input: cerebrocerebellum
1. top-down/descending: cerebral cortex via pons
2. bottom-up/ascending: from vestibular inputs, inferior olive, spinal cord

15

input
1. descending

= cerebral cortex via pons
1. axons synapse on ipsilateral neurones in pontine nuclei
2. pontine nuclei give rise to transverse projections that cross midline (form middle cerebellar peduncle) --> relays cortical signals to contralateral cerebellar hemisphere
- signals derived from one cerebral hemisphere are processed by the neural circuits in the opposite cerebellar hemisphere
- majority arises from primary and pre-motor cortices (frontal), primary and secondary somatic sensory cortices (anterior parietal) and higher order visual regions (posterior parietal)

16

input
2. ascending

= from vestibular inputs, inferior olive, spinal cord
- vestibular and spinal inputs: remain ipsilateral from point of entry in brainstem (travelling inferior cerebellar peduncle)
--> right half of cerebellum is concerned with right part of the body

17

output
1. ascending

a) cerebrocerebellar pathway = to pre-motor + associational cortices of frontal lobe --> motor planning
- feedback loop: collaterals to parvocellular red nucleus in midbrain --> inferior olives
- closed loops: to non-motor areas of the cortex from which signals originated (--> coordination of non-motor programs)
- open loops: input from multiple areas, output to motor cortices
--> run in parallel
b) spinocerebellar pathways = to upper motor neurones --> execution of movement
- laterally positioned interposed nuclei --> via superior peduncle --> thalamus and frontal lobes

18

output
2. descending

a) spinocerebellar pathways = directed to upper motor neurones responsible for execution of movement
- fastigial nuclei (vermis) --> inferior peduncle --> reticular formation + vestibular complex --> give rise to tracts governing axial + proximal limb muscles
b) vestibulocerebellar pathway - inferior peduncle --> vestibular complex that governs movement of eyes, head, neck, compensating for linear + rotational accelerations of the head

19

cellular organisation
- layers

1. molecular layer
- apical dendrites of Golgi cells
2. Purkinje cell layer
- contains Purkinje cell bodies
3. granule cell layer
- contains granule cell bodies

20

cellular organisation
- Purkinje cells

= ultimate destination of afferent pathways
- input from cerebral cortex to Purkinje cells is indirect
- huge dendrites that branch out --> receive input from heaps of parallel fibres
- inhibitory (GABAergic)
- projections to deep cerebellar nuclei that serve to shape discharge patterns

21

cellular organisation
- mossy fibres

= indirect input
- come from all sorts of sources (cortex, brainstem, spinal cord)
- synapse on deep cerebellar nuclei + granule cells
--> granule cells give rise to parallel fibres --> synapse on Purkinje cells

22

cellular organisation
- climbing fibres

= direct input
- inferior olive --> climbing fibres --> Purkinje cell + deep nuclei

23

cellular organisation
- local circuit neurones

= modulate inhibitory output of Purkinje cells by inhibiting them after excitatory input from parallel fibres
1. basket cells: lateral inhibition that may focus spatial distribution of Purkinje cell activity
2. stellate cells

24

cellular organisation
- Golgi cells

= receive input from parallel fibres and then inhibit those exact cells

25

long-term depression

= sensorimotor synapses become less effective due to activation of climbing fibres and parallel fibres at same spot on Purkinje cells

26

mechanisms of LTD

1. climbing fibre activates Purkinje cell
2. Ca2+ influx --> strong depolarisation of Purkinje cell
3. depolarisation mediates/ makes Na+ influx from parallel fibres possible
4. due to strong depolarisation metabotropic glutamate receptors allow influx of PKC

27

functions

- coordination
- fine tuning (timing)
- unconscious planning of motor behaviour
- learning of motor behaviour
- non-motor behaviour

28

functions
- learning

- feedback and error mechanisms
a) implicit learning/ procedural memory:
- learn event sequences
- once learned motor plan, have template of movement in cerebellum
b) associative learning
- random coupling of two stimuli to form association

29

functions
- cognition

- speech production/perception
- emotion processing

30

cerebellar dysfunction

- ataxia: caused by lesions anywhere in fronto-pontine-cerebello-thalamo-cortical loop
- nystagmus = eye fluctuations
- truncal ataxia = inability to stand/sit upright
- gait ataxia = drunken sailor walk
- dysmetria = related to hand movements
- dysdiadochokinesia = difficulty performing rapid alternating movements
- tremor
- slurred, imprecise speech

31

forward model

- cerebellum compares motor signals + sensory input
- is important for prediction + sensorimotor learning
- error signalling