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Chapter 9
The Cerebellum: Ataxia
Cerebellum:
Functions:
Influences the
timing and force
of contractions of
voluntary muscles
Makes movements
coordinated and
smooth
“3” is the key number with the cerebellum:
3 parts (divided sagittally)
3 lobes (divided horizontally)
3 peduncles
3 layers of cortex
3 output nuclei
3 clinical syndromes
Fig.
5-1
Subdivisions of the cerebellum:
(2nd oldest)
(newest)
(oldest)
(superior surface of cerebellum)
(paravermal)
superior surface of cerebellum:
(inferior surface of cerebellum)
inferior surface of cerebellum:
cerebellar tonsils
folia
tonsil
the folia sharing
a common stem
of white matter
form a lobule
tonsillar herniation:
cerebellar tumor
hematoma
Chiari malformation
superior:
mostly output
transverse
middle:
all input
motor
cortex
inferior:
mostly input
dorsal
,etc.
Arbor vitae
(tree of life)
Gray matter
(cerebellar cortex)
white matter
Gray matter layers:
external
molecular
Purkinje
granular
internal
Gray matter
White matter
Fig. 9-5
(all other afferents)
(from inf. olivary nucleus)
Climbing fibers excite Purkinje neurons and cerebellar nuclei
Mossy fibers excite granule neurons and cerebellar nuclei
Granule cells (the only excitatory neuron of the cerebellar cortex)
excite: Purkinje neurons
stellate neurons  inhibit Purkinje neurons
basket neurons  inhibit Purkinje neurons
Golgi neurons  inhibit granule cells
Purkinje neurons (the only output neuron of the cerebellar cortex)
inhibit: all the cerebellar nuclei (to regulate the output
fibers of the cerebellum)
•excited by climbing and mossy fibers
•inhibited by Purkinje cells
Fig. 9-4
(transverse section at pontomedullary junction)
vermis & fastigial nuclei:
control head, trunk, proximal
limb movements bilaterally
hemispheres & the interposed
and dentate nuclei:
control progressively more distal
limb movements ipsilaterally
Fig. 9-7
Posterior lobe (lateral cerebellar hemispheres):
are concerned with learning and storage of all the
sequential components of skilled movements
input: (corticopontocerebellar)
from association areas of
cerebral cortex where desire
to perform volitional movements
occurs
output:
to motor cortex where skilled
movements are represented
Posterior
lobe
circuitry:
Left cerebral
cortex (assoc.areas)
internal capsule
cerebral crus
ipsilateral pontine
nuclei
pontine nuclei
mossy
fibers
transverse pontine
fibers
Input
Fig. 9-8
transverse pontine
fibers (decussate)
middle cerebellar
peduncle
Right posterior
lobe
L motor cortex
VL thalamus
thru contralat. red
nucleus
(decussation)
superior
cerebellar
peduncle
superior cerebellar
peduncle
dentate nucleus
Output
Fig. 9-8
R posterior lobe
Purkinje neurons
Posterior lobe is commonly affected by CVA’s, tumors,
trauma, and degenerative diseases
Fig.
5-1
Posterior lobe syndrome:
intention tremors (volitional)
ataxia
decreased muscle tone
dysmetria
dysdiadochokinesia
dysarthria
rebound phenomenon
*unilateral lesion
 ipsilateral
symptoms
Fig. 9-10
Anterior lobe (vermal and paravermal parts):
input: sensory information from muscular, joint, and
cutaneous mechanoreceptors
output: to limbs (to maintain coordination of limb
movements while skilled movements are being executed)
- lower limbs are represented anteriorly
- upper limbs and head are represented
posteriorly
Anterior lobe circuitry:
Fig. 9-12
anterior part of
ipsilateral anterior lobe
inferior cerebellar
peduncle
dorsal spinocerebellar tract
dorsal nucleus
of Clarke (C8-L2)
gracile tract
muscle spindles,
GTO’s, cutaneous
receptors of the
lower limbs
dorsal nucleus
lower
limb
input
Fig. 2-4
Anterior lobe circuitry:
posterior part of
ipsilat. anterior lobe
Fig. 9-12
cuneocerebellar
tract
inferior cerebellar
peduncle
cuneocerebellar
tract
accessory
cuneate nucleus
cuneate tract
muscle spindles,
GTO’s, cutaneous
receptors of upper
limbs
upper
limb
input
Ventral spinocerebellar
tract:
originates from neurons
in intermediate zone
and anterior horn
(at lumbar levels)
carries information about
ongoing influences of
descending motor
pathways on the spinal
gray matter
decussates twice
(in cord and in superior
cerebellar peduncle)
arrives in anterior lobe
Anterior lobe circuitry:
fastigial
globose
emboliform
Output
vermis  fastigial and
vestibular nuclei and RF
 bilateral influence on head,
neck, and proximal limb
muscles
paravermis  interposed
nuclei  contralateral red
nucleus and RF
 distal limb muscles
Fig. 9-12
Anterior lobe is commonly affected by chronic alcoholism
(malnutrion  degeneration of Purkinje neurons)
Fig.
5-1
Anterior lobe syndrome:
gait instability
walk as if drunk
stagger stiff-legged
difficulty with heel-shin test
gait ataxia
Fig. 9-14
Flocculonodular lobe:
responsible for the coordination of the muscles associated
with equilibrium and eye movements
Flocculonodular lobe
circuitry:
Input and
Output
vestibulo-ocular projections
 external ocular muscles
med. vestibulospinal tract
 bilateral axial muscles
vestibular nuclei and reticular
formation
fastigial nucei
flocculonodular lobe
vestibular nuclei
inferior cerebellar peduncle
direct and indirect vestibulocerebellar fibers
vestibular apparatus (inner ear)
41
Fig. 9-15
Flocculonodular lobe is commonly affected by tumors
(ie. medulloblastomas) in the roof of the 4th ventricle
Fig.
5-1
Flocculonodular
lobe syndrome:
truncal ataxia
Fig. 9-16
lack of coordination
of paraxial muscles
reel and sway from
side to side
Chapter 9 Review
know the three parts of the cerebellum (when divided sagitally)
know the three cerebellar lobes and the fissures that separate them
know the major sources of input into the three lobes of the cerebellum
know the portions of the brainstem each cerebellar peduncle connects to
know the primary type of fiber in the cerebellar peduncles
know the layers of the cerebellar cortex and the cells found in them
know the two ways the cerebellar cortex and cerebral cortex differ
know the circuitry (excitatory and inhibitory connections) of the cerebellar cortex
know the effects of the connections of the climbing and mossy on the cerebellar
nuclei and the cells of the cerebellar cortex
know the cerebellar nuclei and their relationships to each other
know the portions of the cerebellar cortex that project to the cerebellar nuclei
and the movements they control
know the main functions of the three lobes of the cerebellum
know the connections of the three lobes of the cerebellum
know the signs and symptoms associated with the three cerebellar syndromes