Cerebellum Flashcards
Cerebellum
▪ “little brain”
▪ 10% of the brain’s volume but contains 50% of the neurons in the brain
Major role in motor function
Integrates sensory perception with muscle output, but does not initiate motor command
Cerebellum major role in Motor function
▪ maintenance of muscle tone (lesion = hypotonia)
▪ maintenance of posture & balance (lesion = ataxia)
▪ coordination of voluntary motor activity (eye movement, speech, limbs, etc…)
➢ initiation, planning & timing (lesion = dyssynergia)
➢ when to activate, duration, & deactivate
Cerebellum major role in Motor learning
▪ feedforward correction (lesion = dysmetria, intention tremor)
▪ feedback correction in its comparator role
Cerebellum major role in Cognition function
▪ role in processing sensory input (language, music) emotion
Lesions of the cerebellum
▪ exact localization of lesions through signs/symptoms and clinical exam is not
precise and proves challenging
▪ signs/symptoms (functional loss) associated with cerebellar lesions are usually
ipsilateral or bilateral
Cerebellar lesions DOs and DON’Ts
DO impair motor activity - equilibrium, balance, coordination and tone
DO NOT result in motor paralysis
DO NOT impair ability to consciously detect sensory input (visual, auditory, vestibular, somatosensory, etc…)
3 major input/output pathways
1 Superior cerebellar peduncle
2 Middle cerebellar peduncle
3 Inferior cerebellar peduncle
Anatomical division of the Cerebellar cortex
-Vermis
-Medial hemispheres
-Lateral hemispheres
Functional regions/divisions of the Cerebellar cortex
-Vestibulocerebellum
-Spinocerebellum
-Cerebrocerebellum
Deep cerebellar nuclei
Primary output from cerebellum
-Fastigial nucleus
-Interposed nucleus
-Dentate nucleus
Afferents reach cerebellar cortex via what?
All 3 peduncles
Climbing fibers
from inferior olivary nucleus
Mossy fibers
▪ most common input
▪ reach Purkinje cells indirectly (via granule cells)
➢ from most other sources (e.g., vestibular nuclei, spinal cord, reticular
formation, even feedback from deep cerebellar nuclei)
➢ most are from the cerebral cortex
▪ 2nd order neurons via pontocerebellar pathway
Granule cells
parallel fibers are the axons of granule cells
➢ some estimates put their number at 50 billion
▪ about 75% of all neurons in the brain!
Purkinje cells
▪ only fiber type to exit cerebellar cortex
▪ most go to deep cerebellar nuclei
➢ have enormous dendritic trees
▪ as many as 200,000 synapses per Purkinje cell!
Cerebellar efferents
From deep cerebellar nuclei via the superior or inferior cerebellar penduncle
▪ most fibers decussate as they leave the cerebellum
Headed for cortical (via motor thalamus) or brainstem (e.g, red nucleus, inferior olive, vestibular nuclei) targets
Overview of connectivity within cerebellum
▪ climbing fibers → Purkinje cells → deep cerebellar nuclei→outputs
▪ mossy fibers → granule cells → Purkinje cells
Spinocerebellum Function
Motor coordination of posture & ipsilateral limbs
“feedback system”
Vermis (spino-_
➢ role in regulating posture via axial muscle tone & antigravity muscles
➢ role in coordinating trunk movement
Medial hemispheres (spino-)
➢ role in coordinating distal limb movement
▪ compares intended movement with actual movement
* integrates proprioceptive input with motor activity
▪ can ‘fine tune’ movement
* feedback system
Afferents (spino-)
Proprioceptive information from:
-Spinocerebellar tract (LE)
-Cuneocerebellar tract (UE)
-Spinal trigeminal nucleus (head) [Ant. spino- via SCP]
Enter via inferior cerebellar peduncle
Afferents to vermis
▪ trunk/axial components to fastigial nucleus
Efferents (from fastigial) exit via SCP
Decussate CL to motor thalamus (VA/VL)
Afferents to medial hemispheres
▪ limb components to interposed nucleus
➢ neurons here fire during movement, not before
Efferents (from interposed nuclei) exit via SCP
Decussate CL to motor thalamus (VA/VL)
Decomposition of movement
Inability to coordinate balance, gait, extremity and/or eye movements
Truncal ataxia
▪ ‘drunken sailor’ gait
➢ wide-based, uncertain starts & stops, lateral deviations, unequal steps
Rebound phenomena
▪ loss of check reflex
➢ e.g., when flexing arm isometrically against resistance, if resistance is suddenly removed, patient’s arm will flex – perhaps even hitting themselves
Speech scanning (form of dysarthria)
Random volume emphasis of words or syllables
Cerebrocerebellum Function
For motor (procedural) learning; also cognition
▪ most skilled movements: throw a ball, play an instrument, etc.
▪ planning of motor movements
➢ neurons fire before movement
▪ fire after motor association area, but before primary motor cortex
* i.e., “feedforward system”
▪ cognitive aspects of language, speech, and emotional learning
➢ not well understood
Afferents to Cerebrocerebellum
from the contralateral cerebral cortex (via many nuclei in pons)
▪ cortico-pontine-cerebellar pathway
➢ massive input
➢ 10-12x the size of corticospinal tract!
▪ somatotopic
▪ also inputs from other areas of cerebral cortex, e.g., prefrontal areas
Enter via the middle cerebellar peduncle from pontine nuclei
Afferents to lateral hemispheres (cerebro-)
Represent the vast majority of the volume of the cerebellum
To dentate nucleus
Efferents (from dentate nucleus) exit via superior cerebellar peduncle
▪ decussates to contralateral motor thalamus (VL/VA), then on to motor and premotor cortex
Deficit is usually _________ to cerebellar damage.
Impsilateral
Dyssnergia
(sequential movement or jerking)
Changes in timing regulation
Lack of coordination (learned, skillful movements)
Longer to initiate movements
Problems stopping and changing direction
Hypotonia: reduced muscle tone
Reduced spinal reflexes
Dysmetria
“wrong length”
Misjudges the distance
Type of ataxia
-Overshoot or undershoot
-Problems correcting movements may appear similar to intention tremor
▪ different from Parkinsonian intention tremor: not as rhythmic or regular
Inferior Olivary Nucleus
1 located in rostral medulla
2 gets widespread inputs (afferents)
- spinal cord, cerebral cortex, red nucleus, feedback from cerebellum
3 major input to cerebellum via inferior cerebellar peduncle
➢ contralateral
▪ =climbing fibers in cerebellar cortex
4 purpose of circuit (IO→cerebellar cortex→dentate nucleus→red nucleus→IO) is
unclear, but…
- lesions of inferior olive produce symptoms very similar to those of lateral cerebellum
3 cerebellar peduncles “attach” cerebellum to ___________ and transmit input
and output to and from cerebellum
brainstem
Superior Cerebellar Peduncle (SCP)
Gross anatomy:
▪ connects cerebellum to midbrain (pons/midbrain junction)
▪ form the “roof” of the 4th ventricle
Contains mostly efferent fibers
▪ afferent: basically none: a few anterior spinocerebellar afferents pass through
▪ efferent: contains major efferent output from cerebellum
➢ spinocerebellum (trunk components = fastigial nucleus; limb components
= interposed nuclei) and cerebrocerebellum (dentate nuclei) project to thalamus and three brainstem nuclei (red nuclei, reticular nuclei and vestibular nuclei)
Middle Cerebellar Peduncle (MCP)
Largest connection of the three peduncles – major motor pathway of cerebrocerebellar (neocerebellum) entering cerebellum
Gross anatomy:
▪ connects cerebellum to the pons
- contains afferent fibers
▪ afferent:
➢ major motor input from cerebral cortex terminate in pontine nuclei which project to the pontocerebellum (neocerebellum)
➢ also afferent input from reticular nuclei
▪ efferent:
➢ NO EFFERENT outputs pass through middle peduncle
Inferior Cerebellar Peduncle (ICP)
Gross anatomy:
▪ connects cerebellum to medulla
- contains both afferent and efferent fibers
▪ afferent:
➢ proprioceptive input via spinocerebellar tracts project to spinocerebellum (paleocerebellum)
➢ vestibular input from vestibular nuclei and CN 8 project to vestibulocerebellum (flocculonodular lobe)
▪ efferent:
➢ vestibulocerebellum (flocculonodular lobe/fastigial nucleus) projects to vestibular nuclei in brainstem
