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Chapter 15
CEREBELLUM
Dr. Mohammed Alanazy
Outline
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Localization of cerebellar lesions
Cerebellar lobes, peduncles, and deep nuclei
Microscopic circuitry of the cerebellum
Cerebellar output pathways
Cerebellar input pathways
Vascular supply to the cerebellum
Cases
• The cerebellum integrates massive sensory
and other inputs from many regions of the
brain and spinal cord, and uses these inputs to
smoothly coordinate ongoing movements and
to participate in motor planning.
Localization of cerebellar lesions:
– Ataxia is ipsilateral to the side of a cerebellar
lesion.
– Midline lesions of the cerebellar vermis or
flocculonodular lobes mainly cause unsteady gait (
truncal ataxia) and eye movements abnormalities,
which are often accompanied by intense vertigo,
nausea, and vomiting.
– Lesions lateral to the cerebellar vermis mainly
cause ataxia of the limbs ( appendicular ataxia).
Cerebellar lobes, peduncles, and deep nuclei
• The cerebellum consists of a midline vermis, and two large
cerebellar hemispheres.
• Fissures:
– The primary fissure ( separates ant. and post lobes)
– The posterolateral fissure ( separates posterior lobe from
flocculonodular lobe)
• The two flocculi are connected to the midline structure called
the nodulus.
• The nodulus is the most inferior portion of the cerebellar
vermis.
• Cerebellar tonsils: on the inferior portion of the cerebellum (
crucial to know about tonsillar herniation)
• Cerebellar peduncles form the walls of the
forth ventricle.
• Superior cerebellar peduncle = brachium
conjunctivum
• Middle cerebellar peduncle = brachium pontis
• Inferior cerebellar peduncle = resiform body
(ropelike body).
• The superior cerebellar peduncle carries
mainly outputs from the cerebellum.
• The superior cerebellar peduncles decussate
in the midbrain at the level of the inferior
colliculi.
• The middle and inferior carry mainly inputs.
The cerebellum can be divided into three
functional regions, from medial to lateral, based
on their input and output connections:
The deep cerebellar nuclei and vestibular nuclei also fit with this
medial to lateral functional organization.
• All outputs from the cerebellum
are relayed by these nuclei.
• In addition, these nuclei receive
collateral fibers of cerebellar
inputs on their way to the
cerebellar cortex.
The deep cerebellar nuclei are (from lateral to
medial):
• Dentate
• Emboliform
• Globose
• Fastigial
( Don’t Eat Greasy Food)
• The dentate receives projections from the lateral cerebellar hemispheres
• The emboliform and globose (interposed nuclei): inputs from the
intermediate part of the cerebellar hemispheres.
• The fastigial: inputs from the vermis, and a small inputs from the
flocculonodular lobe.
• Most fibers leaving the inferior vermis and flocculi project to the
vestibular nuclei, which function in some ways like additional deep
cerebellar nuclei.
Microscopic circuitry of the cerebellum
• Layers of Cerebellar cortex
• Synaptic inputs
– Mossy fibers
– Climbing fibers
• Inhibitory interneurons in the cerebellar cortex
– Basket cells
– Stellate cells
– Golgi cells
Cerebellar cortex has three layers:
– The molecular
cell layer
– The Purkinje cell
layer
– The granule cell
layer
There are two kinds of synaptic inputs:
• Mossy fibers:
– Arise from numerous regions
– Ascend through cerebellar WM to form excitatory synapses onto
dendrites of granule cells
– Granule cells send axons into the molecular layer, which bifurcate,
forming parallel fibers that run parallel to the folia.
– The parallel fibers run perpendicular to the dendrites of the Purkinje
cells.
– Each parallel fiber forms excitatory synaptic contacts with numerous
Purkinje cells.
– All output from the cerebellar cortex is carried by the axons of
Purkinje cells into the cerebellar wm.
– The Purkinje cells form inhibitory synapses onto the deep cerebellar
nuclei and vestibular nuclei, which then convey outputs from the
cerebellum to other regions through excitatory synapses.
• Climbing fibers:
– Arise exclusively from neurons in the contralateral inferior
olivary nucleus.
– They wrap around the cell body and proximal dendritic
tree of Purkinje cells, forming powerful excitatory
synapses.
– Climbing-fiber inputs have a strong modulatory effect on
the response of the Purkinje cells, causing a sustained
decrease in their response to synaptic inputs from parallel
fibers.
Inhibitory interneurons in the cerebellar cortex
• Basket cells
• Stellate cells
• Golgi cells
Microscopic circuitry of the cerebellum
All axons projecting upward are excitatory. All axons projecting downward are inhibitory.
Cerebellar output pathways
• Lesions of the lateral cerebellum  distal limb
coordination
• Medial lesions  affect mainly trunk control,
posture, balance, and gait.
• Deficits occur ipsilateral to the lesion (why?)
• Output pathways from the cerebellum are double
crossed !
– In superior cerebellar peduncle
– In corticospinal and rubrospinal tracts.
• Each cerebellar hemisphere receives information
about the ipsilateral limbs.
Output from the cerebellum are carried by
Purkinje cells to the deep cerebellar nuclei or
vestibular nuclei.
1. Output from the lateral cerebellar hemisphere
–
Via Dentate nucleus ( motor planning)
2. Output from the intermediate cerebellar hemisphere
–
Via interposed nuclei (influencing laterl motor systems)
3. Output from the cerebellar vermis and flocculonodular lobe
hemisphere
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Via fastigial nucleus ( influencing medial motor system)
The flocculonodular lobe and inferior vermis also have direct
projections to the vestibular nuclei influencing balance and
vestibulo-ocular control.
Output from the lateral cerebellar hemisphere
There is some evidence that output
from the lateral cerebellum relay in the
thalamus to reach the prefrontal
association cortex, possibly playing a
role in cognitive function
Motor, premotor,
supplementary
motor area
Parietal lobe influence
motor planning in the
corticospinal system.
Output from the intermediate cerebellar hemisphere
III CN
Vestibulo-ocular reflexes
and
Smooth pursuit
VI
CN
Influence
anterior
corticospinal
tract
ML
F
Tectospinal
Equilibrium and balance
The Vestibulo-Ocular Reflexes
•
Because of inertia, rotation of
the head in a counterclockwise
direction causes endolymph to
move clockwise with respect
to the canals. This reflects the
stereocilia in the left canal in
the excitatory direction,
thereby exciting the afferent
fibers on this side. In the right
canal the hair cells are
hyperpolarized and afferent
firing there decreases.
Horizontal Vestibulo-Ocular reflex
Cerebellar input pathways
• Inputs to the cerebellum have a rough somatotopic organization, with the
ipsilateral body represented in both the anterior and posterior lobes.
Cerebellar input pathways
1. Corticopontine fibers
Frontal, temporal, parietal, occipital cortices
Internal
capsule
Cerebra
l
peduncl
es
cerebellum
Pontine
nuclei
2. Spinocerebellar fibers
Dorsal spinocerebellar ( LE) and
Cuneocerebellar tracts(UE):
Unconscious information reach the
ipsilateral cerebellum provide rapid
feedback to the cerebellum about
ongoing limb movements, allowing
fine adjustments to be made.
Arms
Legs
Ventral spinocerebellar ( LE) and rostral
spinocerebellar ( UE) tracts:
Information about activity of spinal
cord interneurons
3. Inferior olivary nucleus
Climbing fibers
Inferior cerebellar peduncle
4. Vestibular inputs
• Fibers from vestibular ganglia and vestibular
nuclei project to the ipsilateral inferior
cerebellar vermis and flocculonodular lobe via
the juxtarestiform body.
Inferior cerebellar peduncle: consists of two divisions:
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Restiform body is an afferent fiber system containing:
(1) Dorsal spinocerebellar tract
(2) Cuneocerebellar tract
(3) Olivocerebellar tract
Juxtarestiform body contains afferent and efferent fibers:
(1) Vestibulocerebellar fibers (afferent)
(2) Cerebellovestibular fibers (efferent)
Middle cerebellar peduncle connects the cerebellum to the pons
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pontocerebellar fibers to the neocerebellum.
Superior cerebellar peduncle connects the cerebellum to the pons and midbrain.
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represents the major output from the cerebellum.
Efferent pathways
(1) Dentatorubrothalamic tract
(2) Interpositorubrothalamic tract
(3) Fastigiothalamic tract
(4) Fastigiovestibular tract
Afferent pathways
(1) Ventral spinocerebellar tract
(2) Trigeminocerebellar fibers
(3) Ceruleocerebellar fibers
Vascular supply to the cerebellum
•Lateral medulla,
•most of the inferior half
of the cerebellum,
• the inferior vermis
•Inferior lateral pons,
• MCP, and
• a strip of anterior cerebellum
•Flocculus
•Upper lateral pons,
•SCP,
•most of the superior half of the
cerebellum,
•deep cerebellar nuclei and
•superior vermis
Clinical pearls
• Infarcts are more common in PICA and SCA
• Often, lateral medulla and pons are involved:
– Look for brainstem signs and symptoms
• Infarct that spare lateral brainstem and involve
mainly cerebellum are more common with SCA.
• Large infarct can cause swelling of the cerebellum
hydrocephalus or brainstem compression and
tonsilar herniation.( monitor pt closely for at least 72
hours)
• Same with cerebellr hemorrhage
• If you see a patient with
– Wide-based, unsteady “drunklike gait”
• Truncal ataxia
• Lesion in cerebellar vermis
– Ataxia on movement of the limbs only
• Appendicular ataxia
• Lesion in ipsilateral cerebellar hemisphere sparing the
vermis
– Both of the above
• Lesion in the cerebellar hemisphere extending to the
vermis
False localization of ataxia
• Lesion of the cerebellar peduncles or pons can
produce severe ataxia without involvement of
cerebellar hemispheres
• Can produce gait abnormalities resemble cerebellar
truncal ataxia:
– Hydrpcephalus ( may damage frontopontine pathways
– Lesions of the prefrontal cortex
– Spinal cord lesions
• Ataxic hemiparesis
– Lesion in corona radiate, internal capsule, or pons,
disrupting corticospinal and corticopontine fibers
• Sensory ataxia