Cerebellum

Question 1

Cerebellum

Answer 1

▪ “little brain”
▪ 10% of the brain’s volume but contains 50% of the neurons in the brain

Question 2

Major role in motor function

Answer 2

Integrates sensory perception with muscle output, but does not initiate motor command

Question 3

Cerebellum major role in Motor function

Answer 3

▪ 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

Question 4

Cerebellum major role in Motor learning

Answer 4

▪ feedforward correction (lesion = dysmetria, intention tremor)
▪ feedback correction in its comparator role

Question 5

Cerebellum major role in Cognition function

Answer 5

▪ role in processing sensory input (language, music) emotion

Question 6

Lesions of the cerebellum

Answer 6

▪ 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

Question 7

Cerebellar lesions DOs and DON’Ts

Answer 7

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…)

Question 8

3 major input/output pathways

Answer 8

1 Superior cerebellar peduncle
2 Middle cerebellar peduncle
3 Inferior cerebellar peduncle

Question 9

Anatomical division of the Cerebellar cortex

Answer 9

-Vermis
-Medial hemispheres
-Lateral hemispheres

Question 10

Functional regions/divisions of the Cerebellar cortex

Answer 10

-Vestibulocerebellum
-Spinocerebellum
-Cerebrocerebellum

Question 11

Deep cerebellar nuclei

Answer 11

Primary output from cerebellum
-Fastigial nucleus
-Interposed nucleus
-Dentate nucleus

Question 12

Afferents reach cerebellar cortex via what?

Answer 12

All 3 peduncles

Question 13

Climbing fibers

Answer 13

from inferior olivary nucleus

Question 14

Mossy fibers

Answer 14

▪ 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

Question 15

Granule cells

Answer 15

parallel fibers are the axons of granule cells
➢ some estimates put their number at 50 billion
▪ about 75% of all neurons in the brain!

Question 16

Purkinje cells

Answer 16

▪ 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!

Question 17

Cerebellar efferents

Answer 17

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

Question 18

Overview of connectivity within cerebellum

Answer 18

▪ climbing fibers → Purkinje cells → deep cerebellar nuclei→outputs
▪ mossy fibers → granule cells → Purkinje cells

Question 19

Spinocerebellum Function

Answer 19

Motor coordination of posture & ipsilateral limbs
“feedback system”

Question 20

Vermis (spino-_

Answer 20

➢ role in regulating posture via axial muscle tone & antigravity muscles
➢ role in coordinating trunk movement

Question 21

Medial hemispheres (spino-)

Answer 21

➢ role in coordinating distal limb movement
▪ compares intended movement with actual movement
* integrates proprioceptive input with motor activity
▪ can ‘fine tune’ movement
* feedback system

Question 22

Afferents (spino-)

Answer 22

Proprioceptive information from:
-Spinocerebellar tract (LE)
-Cuneocerebellar tract (UE)
-Spinal trigeminal nucleus (head) [Ant. spino- via SCP]

Enter via inferior cerebellar peduncle

Question 23

Afferents to vermis

Answer 23

▪ trunk/axial components to fastigial nucleus
Efferents (from fastigial) exit via SCP
Decussate CL to motor thalamus (VA/VL)

Question 24

Afferents to medial hemispheres

Answer 24

▪ 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)

Question 25

Decomposition of movement

Answer 25

Inability to coordinate balance, gait, extremity and/or eye movements

Question 26

Truncal ataxia

Answer 26

▪ ‘drunken sailor’ gait ➢ wide-based, uncertain starts & stops, lateral deviations, unequal steps

Question 27

Rebound phenomena

Answer 27

▪ 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

Question 28

Speech scanning (form of dysarthria)

Answer 28

Random volume emphasis of words or syllables

Question 29

Cerebrocerebellum Function

Answer 29

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

Question 30

Afferents to Cerebrocerebellum

Answer 30

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

Question 31

Afferents to lateral hemispheres (cerebro-)

Answer 31

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

Question 32

Deficit is usually _________ to cerebellar damage.

Answer 32

Impsilateral

Question 33

Dyssnergia

Answer 33

(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

Question 34

Dysmetria

Answer 34

"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

Question 35

Inferior Olivary Nucleus

Answer 35

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

Question 36

3 cerebellar peduncles “attach” cerebellum to ___________ and transmit input and output to and from cerebellum

Answer 36

brainstem

Question 37

Superior Cerebellar Peduncle (SCP)

Answer 37

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)

Question 38

Middle Cerebellar Peduncle (MCP)

Answer 38

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

Question 39

Inferior Cerebellar Peduncle (ICP)

Answer 39

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