9/14 Cerebellum - Rasin Flashcards
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
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
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
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
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
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!
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:
- output of lateral hemi → dentate nucleus
- output of intermediate hemi → interposed nuclei
- output of vermis → fastigial nucleus
- output of flocculonodular lobe → vestibular nuclei
cerebellar peduncles
associated with 3 parts of brainstem:
- superior cerebellar peduncles → midbrain
- middle cerebellar peduncles → pons
- inferior cerebellar peduncles → medulla
*can see through tractography
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:
- 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!
- VL nucleus of thalamus
- → projection to motor cortex, association cortex
- communication to region where movement is initiated
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
GuillanMollaret triangle
dentate nucleus (contralat) → red nucleus (parvocellular red nucleus) → inf olivary nucleus → dentate nucleus (contralat)
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
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
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
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)
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
relationship of cerebellum and motor systems
pathways descending from cortex to influence motor control:
-
corticopontine tract (plan for action) → internal capsule → cerebral peduncles → midbrain → pontine nuclei
* communicates plan via MCP on contralateral side (bc pontocerebellar fibers are crossing) - 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
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
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:
- outer: molecular - stellate cells, basket cells
- middle: Purkinje cell
- inner: granular - granule cells, Golgi cells
*granule cells are only glutamate (excitatory) cells! all others are GABA (inhibitory)
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
2 main lines of input for Purkinje cells
- climbing fibers from contralat inferior olivary nucleus - excitatory
- mossy fibers from contralat pontine nuclei - excitatory
- both are excitatory for Purkinje cells, which are inhibitory
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
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
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
- hypotonia
- postural changes, altered gait
- disturbance of voluntary movement (ataxia)
- dysdiadochokinesis
- disturbances of reflexes
- disturbances of ocular movement (nystagmus)
- disorders of speech (dysarthria)
common diseases involving cerebellar disease
- congenital agenesis or hypoplasia
- neoplasms
- trauma
- infection
- thrombosis of cerebellar arteries
- degen disorders (ex. MS)
hallmark cerebellar sign
ataxia (lack of coordination)
- truncal
- appendicular
- speech
- eye movements
anterior lobe syndrome
general ataxia (legs > arms)
broad-based, staggering gait (“drunken gait”)
causes:
- toxin ingestion (chronic alcoholism)
- thiamine_B1 deficiency: Wernicke-Korsakoff syndrome
* memory impairment, confusion, gait ataxia, oculomotor disorders
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
flocculonodular lobe (vestibulocerebellar) syndrome
ex. medulloblastoma (malignant), astrocytoma (benign)
- truncal ataxia (widebase gait)
- titubation (tremor of trunk)
- poor balance
- abnormal eye movements (nystagmus)
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
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
slides for review at end of lecture
check them out
