9/14 Cerebellum - Rasin Flashcards Preview

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Flashcards in 9/14 Cerebellum - Rasin Deck (32):
1

cerebellum: volume and % neurons

10% of brain volume

50% of all neurons

 

largest part of hindbrain (aka "little brain"), located in posterior fossa

  • tentorium cerebelli on top

2

cerebellar tonsillar herniation

through foramen magnum → leads to compression of medulla (resp, cardiovasc, vagus dorsal motor nucleus of X, nucleus solitarius, etc)

can be due to...

  • high ICP
  • Chiari I malformation

3

major components of cerebellum

cerebellar cortex

  • cerebrocerebellum
  • spinocerebellum
  • vestibulocerebellum

deep cerebellar nuclei

  • dentate nucleus
  • interposed nuclei (comprised of 2 nuclei)
  • fastigial nucleus

cerebellar peduncles

  • superior peduncle
  • middle peduncle
  • inferior peduncle

4

organization of cerebellum

2 cerebellar hemispheres joined by narrow median vermis

​divided into 3 lobes:

  • anterior
  • posterior
  • flocculonodular

in addition,

  • vermis+intermediate hemispheres = spinocerebellum
  • lateral hemispheres = cerebrocerebellum

5

functional subdivisions of cerebellum

spinocerebellum

  • intermedial hemi: gross limb movements
  • vermis: eye movements, prox muscles
    • note somatotopic org! lateral is distal, medial is more prox

cerebrocerebellum

  • planning, execution of skilled and complex spatio-temporal sequences (incl speech)

vestibulocerebellum (flocculonodular lobe)

  • posture, equilibrium

6

functional organization of output from cerebellum

 

how does cerebellum stay ipsilateral???

info must end up on appropriate side!

 

cerebellar cortex → deep cerebellar nuclei → decussates, sends info to...

  • red nucleus (midbrain) [→ VL_thalamus]
  • VL complex (thalamus)

→→→ primary motor and premotor cortex!

 

cerebellum innervates ipsilateral movements because it decussates to sends info to the CONTRALATERAL primary motor/premotor cortex!!!

  • cortex → CST, which will re-decussate on way down to LMNs!

7

deep cerebellar nuclei

 

which cerebellar outputs go to which nuclei?

from lateral to medial: don't eat greasy food

  • dentate nucleus
  • emboliform nucleus [one of interposed nuclei]
  • globosus nucleus [one of interposed nuclei]
  • fastigial nucleus

 

output → nucleus:

  1. output of lateral hemi → dentate nucleus
  2. output of intermediate hemi → interposed nuclei
  3. output of vermis → fastigial nucleus
  4. output of flocculonodular lobe → vestibular nuclei

8

cerebellar peduncles

associated with 3 parts of brainstem:

  • superior cerebellar peduncles → midbrain
  • middle cerebellar peduncles → pons
  • inferior cerebellar peduncles → medulla

*can see through tractography

9

output from dentate nuclues

 

 

where is info going? through what tracts

info from dentate nucleus (lateral hemis) carried in superior cerebellar peduncles → decussates at decussation of superior cerebellar peduncles on way to:

1. red nucleus (parvocellular red nucleus)

  • parvocellular red nucleus sends projection back down through central tegmental tract to ipsi inferior olivary nucleus → projection decussates and forms olivocerebellar fibers
  • completely diff from rubrospinal tract!

2. VL nucleus of thalamus

  • → projection to motor cortex, association cortex
  • communication to region where movement is initiated

 

 

10

inferior olivary nucleus

receives inputs from spinal cord, red nucleus, cortex

  • projects to entire cerebellum through contralateral ICP (inf cerebellar peduncle)

source of climbing fibers

 

imp for motor learning

11

GuillanMollaret triangle

dentate nucleus (contralat) → red nucleus (parvocellular red nucleus) → inf olivary nucleus → dentate nucleus (contralat)

12

intermediate output

 

where is info going/ through what tracts

info from interposed nuclei (emboliform & globosus nuclei) carried in superior cerebellar peduncles → decussates at decussation of superior cerebellar peduncles on way to:

1. red nucleus (magnocellular red nucleus)

  • magnocellular red nucleus sends projection back down through ventral tegmental decussation in the rubrospinal tract
  • rubrospinal tract: movement of contralat extremities

2. VL nucleus of thalamus

→ projection to motor cortex, association cortex

  • communication to region where movement is initiated

 

13

what are the inputs to the cerebellum?

 

middle cerebellar peduncle

main inputs are from cortex

  • frontal cortex
  • parietal cortex

cortex → corticopontine fibers travelling through internal capsule and cerebral peduncles, ending on pontine nuclei

  • pontine nuclei → pontocerebellar fibers decussate via middle cerebellar peduncle on way to lateral cerebellar cortex/deep nuclei

*** middle cerebellar peduncle is comprised entirely of INPUTS TO CEREBELLUM from contralat pontine nuclei ***

 

 

another large input: inferior cerebellar peduncles 

14

what are the inputs to the cerebellum?

 

inferior cerebellar peduncle

ICP aka "restiform body" contains inputs and outputs from medulla and spinal cord

contains:

1. dorsal spinocerebellar tract: leg proprioceptors in nucleus dorsalis of Clark → ICP to cerebellum

  • travels ipsilaterally
  • ventral spinocerebellar tract decussates to contralat side within spinal cord, travels/ascends contralaterally → uses superior cerebellar peduncles to cross BACK to ipsilat side

2. cuneocerebellar tract: arm proprioceptors in external cuneate nucleus → ICP to cerebellum

  • travels ipsilaterally

lets you know where your limbs are! so you know if your plan was executed correctly and/or plan for next movement

3. climbing fibers from inferior olivary nucleus 

 

15

cerebellum has no direct connections to any LMNs!

how does it influence LMN action?

either hits:

  • red nucleus → rubrospinal tract
  • VP_thalamus → cortex → lateral and medial motor pathways
  • vestibular nuclei → LMN in spinal cord and brainstem (balance, vestibulo-ocular reg)

16

output from vermis/flocculonodular node

cerebellar cortex → fastigial nucleus → travels through inf cerebellar peduncle to...

  • superior colliculus → gives rise to tract that decussates immediately, descends as tectospinal tract
  • reticular formation

 

17

relationship of cerebellum and motor systems

pathways descending from cortex to influence motor control:

 

1. corticopontine tract (plan for action) → internal capsule → cerebral peduncles → midbrain → pontine nuclei

  • communicates plan via MCP on contralateral side (bc pontocerebellar fibers are crossing)

2. corticospinal tract → internal capsule → through midbrain, pons, to medullary pyramids → decussate and descend to synapse on LMNs that will lead to the action

 

info that you moved is going to be picked up via DRG sensory neurons → dorsal Clarke's nucleus → dorsal spinocerebellar tract travelling ipsilat → through ICP to get to ipsilat cerebellum

cerebellum sends feedback through SCP (and decussation of SCP to contralat side) to:

  • red nucleus → rubrospinal tract which decussates and descends to provide corrective instructions to the LMNs!
  • VL_thalamus → provides feedback info to cortex re: success/failure of intended action and what actually happened

18

how do you get better with practice?

part of the information delivered to red nucleus is going to parvocellular red nucleus → ipsilat inferior olivary nucleus → lateral cerebellar cortex which stores information

  • first part of CNS that will be activated before you make your next movement
  • lateral portions of cerebellar cortex communicate via SCP to VL_thalamus to cortex: activate THIS set of neurons, not the others in order to perform THIS desired action

implication:

  • triangle involving lateral cerebellum is critical for learning movements
  • rubrospinal tract involving spinocerebellum (medial portions) is critical for correction of ongoing movement

19

microscopic circuitry of cerebellum

 

basic structure

3 layers

nt

cortex of cerebellum is folded into folia

  • each has a core of white matter, covered superficially by gray matter

cortex divided into 3 layers:

  1. outer: molecular - stellate cells, basket cells
  2. middle: Purkinje cell
  3. inner: granular - granule cells, Golgi cells

 

*granule cells are only glutamate (excitatory) cells! all others are GABA (inhibitory)

20

Purkinje cells

associated cells

Purkinje cells synapse on deep cerebellar nuclei 

  • each Purkinje cell is associated with one climbing fiber which makes thousands of connections with it
  • granule cells are also associated with Purkinje cells via parallel fibers
    • not 1:1! 
    • granule cells are innervated by mossy fibers

21

2 main lines of input for Purkinje cells

  1. climbing fibers from contralat inferior olivary nucleus - excitatory
  2. mossy fibers from contralat pontine nuclei - excitatory
  • both are excitatory for Purkinje cells, which are inhibitory

22

overall function of cerebellum

coordinate all reflex and voluntary muscular activity (especially if learned)

 

  • motor planning: feed-forward (prior to movement)
    • build movement based on exp, plan for anticipated outcomes/feedback
  • motor execution: feed-back (after movement)
    • compare anticipated outcome to actual: comparator fx
  • motor learning: adjustments to the program

23

vascular supply of cerebellum

PICA: lower cerebellum, lateral medulla

  • nodulus

AICA: lateral caudal pons

  • most of flocculonodular lobe
  • all peduncles (SCP, MCP, ICP)

SCA: lateral rostral pons, superior cerebellum

  • anterior lobe

24

cerebellar lesions → what side sx?

specific lobes: sx

 

signs/sx of cerebellar disease

cerebellar lesions produce IPSILATERAL SX

  • vermis, flocculonodular lobe lesions → trunk axial mm, eye movement

 

  1. hypotonia
  2. postural changes, altered gait
  3. disturbance of voluntary movement (ataxia)
  4. dysdiadochokinesis
  5. disturbances of reflexes
  6. disturbances of ocular movement (nystagmus)
  7. disorders of speech (dysarthria)

25

common diseases involving cerebellar disease

  1. congenital agenesis or hypoplasia
  2. neoplasms
  3. trauma
  4. infection
  5. thrombosis of cerebellar arteries
  6. degen disorders (ex. MS)

26

hallmark cerebellar sign

ataxia (lack of coordination)

 

  • truncal
  • appendicular
  • speech
  • eye movements

27

anterior lobe syndrome

general ataxia (legs > arms)

broad-based, staggering gait ("drunken gait")

 

causes:

1. toxin ingestion (chronic alcoholism)

2. thiamine_B1 deficiency: Wernicke-Korsakoff syndrome

  • memory impairment, confusion, gait ataxia, oculomotor disorders 

28

posterior lobe syndrome

more severe hypotonia (than otherp arts of cerebellum lesioned)

cerebellar ataxia with postural instability

 

  • rebound phenomenon (inability to stop actively flexed hand when released - pt might hit themselves in the face!)
  • decomposition of movements, dysmetria with past pointing, adidochokinesis

*cerebellar nystagmus unlikely to occur with injuries to hemispheric posterior lobe

29

flocculonodular lobe (vestibulocerebellar) syndrome

ex. medulloblastoma (malignant), astrocytoma (benign)

 

  • truncal ataxia (widebase gait)
  • titubation (tremor of trunk)
  • poor balance
  • abnormal eye movements (nystagmus)

30

injuries to cerebellar peduncles

ICP (dorsal spinal cerebellar tract, cuneocerebellar tract)

  • cerebellar ataxia w falling to side of injury
  • hypotonicity
  • maybe cerebellar nystagmus

MCP

  • cerebellar ataxia (not so much falling)
  • hypotonicity
  • maybe hypotonicity of facial muscles

SCP (affects output of cerebellum - cant report that things need to be corrected)

  • cerebellar ataxia and hypotonicity with falling to side of injury
  • marked cerebellar tremor
  • poss asthenia of upward gaze

31

injuries to deep cerebellar nuclei

 

unilat lesion of fastigial, dentate nuclei

unilateral lesion of fastigial nucleus

  • cerebellar nystagmus

unilateral lesion of dentate nucleus

  • unilat cerebellar tremor of lumb (upper > lower)
  • marked ataxia of involved limb

32

slides for review at end of lecture

check them out

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