THE CEREBELLUM
“ The little brain”
.
• Small in total volume compared to the
cerebral cortex, but it contains about ~65-69
billion neurons
• There are about 3.6 times as many neurons in
the cerebellum as in neocortex, a number that
is conserved across many different
mammalian species.
• It takes up only 10% of total brain volume
Fibers of
internal capsule
3rd ventricle
Superior
colliculus
Inferior
colliculus
Vermis
Paravermal zone Vermis
Vestibulocerebellum
Spinocerebellum
Neocerebellum
Hemisphere
Anterior lobe
Primary fissure
Horizontal fissure
L = Lingula
F = Flocculus
N = Nodulus
Tonsil
Flocculonodular
lobe
.
• Axial MRI through medulla of brainstem showing cerebellar
hemispheres and vermis. Abbreviations: M, medulla; V, vermis
B. Cerebellar connections
.
.
A. Cerebellar afferents(input):
1. Cortical input (contralateral) via the middle cerebellar
peduncle after synapsing in the pontine nuclei.
 It receives extensive input from all four lobes of
the cerebral cortex via the pontine nuclei
2. Spinal (somatosensory, ipsilateral) input
Obtains constant feedback from the periphery with
regard to the relative position and state of activity
of our limbs and muscles.
3. Other major input from the level of the brainstem
originates in the vestibular nuclei and ganglion, the
lateral reticular nuclei, and the inferior olivary nucleus.
Connections
Fronto-pontine fibers
Temporo-pontine fibers
Parieto-pontine fibers
Occipito-pontine fibers
Cortico-bulbar (and
Cortico-spinal) fibers
Inferior olivary nucleus
Dorsal spino-cerebellar tract
Dorsal nucleus of clarke
Olivo-cerebellar fibers
.
B. Cerebellar efferents(output):
1. To the cerebral cortex via the thalamus
-to the sensorimotor and executive regions of the
cerebral cortex via the thalamus
2. To the vestibular nuclei in the brainstem
3. To the spinal cord
C. Cerebellar nuclei
.
.
4 Nuclei
1. Fastigial nucleus
2. Globose nucleus
3. Emboliform nucleus
4. Dentate nucleus
• These nuclei are the output nuclei of the
cerebellum to other parts of the central nervous
system
-
Fastigial n.
Cortico-pontine fiber
Globose n.
Emboliform n.
Dentate n.
Pontocerebellar
fiber
Spino-cerebellar fiber
Lateral vestibular n.
-
• The globose and emboliform nuclei are
functionally related and together are often
referred to as the nucleus interpositus
• The largest and most recently developed of
the cerebellar nuclei, the dentate nuclei are
located most laterally
– Input is primarily from the cerebellar
hemisphere
– project primarily to the thalamus
D. Cerebellar Peduncles
.
.
3 Peduncles
1. Inferior Cerebellar Peduncles
2. Middle Cerebellar Peduncles (“brachium
pontis”)
3. Superior Cerebellar Peduncles “brachium
conjunctivum”
-
Cerebellar
peduncles as
seen from
their points of
connection to
the posterior
(dorsal)
surface of the
brainstem
.
1. Inferior Cerebellar Peduncles
• A number of pathways in the spinal cord that
enter the cerebellum via the inferior cerebellar
peduncle (restiform body)
– Convey proprioceptive and other
somatosensory information.
2. Middle Cerebellar Peduncles
• The largest of the three cerebellar peduncles
• The primary pathway by which the cerebral cortex
influences the cerebellum
– Corticofugal
– corticopontocerebellar
Inferior Cerebellar Peduncles
Dorsal spinocerebellar and cuneocerebellar
tracts entering via the inferior cerebellar
peduncle.
.
Cerebropontocerebellar pathways.
.
3. Superior Cerebellar Peduncles
• The major output channel for the cerebellum
• Most efferents from the cerebellum -various
motor pathways
– Allow for the modulation of motor activity by
the cerebellum at different levels and stages of
programming and execution
E. Functions of Cerebellum
.
.
1. Motor Functions of Cerebellum
2. Non-Motor Functions of the
Cerebellum?
.
1. Motor Functions of Cerebellum
a. Balance and Equilibrium
b. Whole Body Coordination - as walking or
running
c. Discrete, Voluntary Limb Movements
d. Eye Movements and Hand-Eye Coordination
.
a. Balance and Equilibrium
• Vestibulocerebellar pathways to
flocculonodular lobe and vermis supplies
information about changes in position/motion.
• Ascending tracts to vermal and paravermal
regions provides feedback concerning position
of head and body in space and state of
contraction of musculature of limbs.
Cerbellar -Fastigiovestibular and
fastigioreticular -pathways give rise to
vestibulospinal and medial reticulospinal tracts
that appear to primarily adjust or facilitate
contraction of antigravity muscles.
b. Whole Body Coordination (e.g. walking or
running)
• Spinocerebellar tracts to vermal and paravermal
regions provides information regarding position
of the body in space and state of contraction of
musculature of limbs.
• Olivocerebellar tracts provide cerebellum
(particularly vermal and paravermal regions) with
integrated information from both cerebral cortex
and spinal cord.
Finally through the ventral and lateral
corticospinal and the rubrospinal tracts that help
control routine, whole body movements such as
walking or running.
-
.
c. Discrete, Voluntary Limb Movements
• Cerebral cortex, via the pontocerebellar
pathways, provides cerebellum with
information about intended action and the
context (internal and external) in which this
action is to take place.
• Spinocerebellar tracts to vermal and
paravermal regions provides information
regarding the position and attitude of the limb,
as well as the body in general, both at the
initiation and during the course of movement.
.
d. Eye Movements and Hand-Eye Coordination
• Information about the position and movement of
the eyes comes into the cerebellum at least
indirectly from the inferior olivary complex via the
olivocerebellar tract and possibly through other,
even more direct pathways (e.g., via pontine nuclei
from the superior colliculus).
• Vestibulocerebellar pathways to flocculonodular
lobe and vermis supplies information about
changes in position/motion, especially of the head.
• Finally through MLF and the cranial nerves III, IV,
and VI - eye movements according to changes in
head movement or position.
2. Non-Motor Functions of the
Cerebellum?
.
.
– Cognitive processes (e.g., executive and
visual-spatial skills, language, memory),
• result from insults to the posterior
hemispheres,
– Behavioral disturbances (e.g., changes in
personality, affect, or autonomic
phenomena).
• with the anterior, vermal regions of the
cerebellum.
F. Lesions of Cerebellum
(motor disturbances)
.
.
1. Loss of Balance
• Whether sitting or standing, we are constantly
making subtle adjustments to our posture in
order to remain vertically stable
– Accomplished largely by the
vestibulocerebellum.
– Disturbances manifested by a wide-based
stance
– Tested clinically by
• having the patient stand with feet
together or
• ask the patient to sit upright or to walk.
.
2. Asynergy
 the “decomposition” of movement "e.g. such
as rapid pronation and supination; Tapping
out rhythms
3. Ataxia
 is the inability to properly regulate the
direction, rate, extent, and intensity of
movements.
– Disturbances of gait - wide-based gait, a
tendency to fall or sway
4. Dysmetria
 A tendency to overshoot or fall short of the
intended goal
5. Tremor
 Most typical is the so-called intention tremor
-
6. Ocular Findings
• Nystagmus - the most common eye finding
with cerebellar disease
– The patient may complain of diplopia
(double vision) or a blurring of vision.
7. Speech Disturbance
 dysarthric -halting, uneven, irregular, poorly
modulated, explosive, or scanning