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The Huilan Nervous Systen: An Andlomical Viewoint,
Sinh Ediliol,Mlnay L. Bd and John A. Kiemm. J.B.
Lippincott Compant Philadelphia, @ 1993.
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The hemispheres, vermis, flocculus, nodule, and tonsil are major landmarks of the cerebellar corte:<.
Afferent fibers end in the three-layered cerebellar cortex. The Purkinje cells
have axons that end in the cerebellar nuclei.
The fastigial, interposed, and dentate nuclei receive branches of all cerebellar afferent fibers and the output of the cor'tex. These nuclei contain the
cerebellar efferent neurons.
The superior cerebellar peduncle contains cerebellar efferent fibers and the
ventral spinocerebellar tract. The middle cerebellar peduncle consists of
fibers from the contralateral pontine nuclei, and the inferior cerebellar
peduncle contains olivocerebellar and dorsal spinocerebellar fibers and the
vestibulocerebellar and fastigiobulbar connections'
The vestibular system is connected ipsilaterally with the vestibulocerebellum, which comprises the flocculonodular lobe and the fastigial
nucleus. This nucleus projects to the ipsilateral vestibular nuclei and to the
reticular formation.
hoprioceptive signals are carried ipsilaterally to the spinocerebellum,
which consists of vermis, paravermal zones, and interposed nuclei' These
nuclei project to the contralateral ventrolateral (VL) thalamic nucleus. The
VL projects to the primary motor corto(.
The cerebral cortex influences the contralateral cerebellar hemisphere and
dentate nucleus (pontocerebellum) by way of a relay in the pontine nuclei,
The dentate nucleus projects to the contralateral VL thalamic nucleus.
These connections determine that each side of the body is represented
ipsilaterally in the cerebellum and that postural functions are localized in
and near the midline,
The cerebellum learns and executes instructions for movements, ensuring
coordination of the force, extent, and duration of the contractions of muscles.
A lesion in or near the midline cause disorders of posture and gait, whereas
a lesion in a hemisphere causes defective control of movements of the
ipsilateral limbs.
163
164
Reglonal Aflotorny of the Central Neruous system
Although the cerebellum has an abundant input from sensory receptors, it is essentially a
motor part of the brain, functioning in the
maintenance of equilibrium and in the coordination of muscle contractions. The cerebellum makes a special contribution to synergy of muscle action (ie, to the synchronized
contractions and relaxations of different muscles that make up a useful movement). The
cerebellum ensures that there is contraction of
the proper muscles at the appropriate time,
each with the correct force. There is reason to
believe that the cerebellum participates in the
of
patterns of neuronal activity
needed for carrying out movements and also
leaming
in the execution of these encoded instructions.
The cerebellum increased in size in the course
of vertebrate evolution, The large size in the
human brain coincides with the need for synergy of muscles, especially for maintenance of
the erect posture and in leamed activities that
require precisely orchestrated hand move_
ments.
Despite their complexity, the activities of
the cerebellum have long been thought to occur without any conscious awareness. This
traditional viewpoint may not be entirely correct: imagined movements are accompanied
by an increase in cerebellar blood flow that is
larger than the increase detected in the motor
areas of the cerebral cortex. Damage to the
cerebellum causes disturbances of motor func-
tion without voluntary paralysis.
The cerebellum consists of a cortex, or
surface layer, of gray matter contained in
transverse folds or folia, a medullary center of
white matter, and four pairs of central nuclei
embedded in the medullary center. Three pairs
of cerebellar peduncles, composed of nerve
fibers, connect the cerebellum with the brain
stem.
oss
Anatomy
The superior cerebellar surface is elevated in
the midline, conforming to the dural reflection
or tentorium that forms a roof for the posterior
cranial fossa. The inferior surface is deeply
grooved in the midline; the remainder of this
surface is convex on each side and rests on the
floor ofthe posterior cranial fossa (Fig. I0-I1.
Certain terms are useful to identify regions
of the cerebellar surface. The region in and
near the midline is known as the vermis and
the remainder, as the hemispheres. The superior vermis is not demarcated from the
hemispheres, but the inferior vermis lies in a
deep depression (the vallecula) and is well
delineated. The term paravermal zone is
used for the medial parts of the hemispheres
for
I
to 2 cm on either side of the vermis.
Three major regions, the flocculonodular,
anterior, and posterior lobes, are recognized
in the horizontal plane (see Fig. I0-l). The
flocculonodular lobe (or lobule) is a small
component, the oldest phylogenetically, that
lies at the rostral edge of the inferior surface.
The nodule is the rostral portion of the inferior vermis, and the flocculi are irregularly
shaped masses on each side. The cerebellum
is deeply indented by several transverse fissures. The dorsolateral fissure (also called
the posterolateral fissure) along the caudal
border of the flocculonodular lobe is the firsr
of these to appear during erhbryonic development. The main mass of the cerebellum (all
but the flocculonodular lobe) consists of dnterior and posterior lobes. The anterior lobe is
that part of the superior surface rosfial to the
primary fissure,I The remainder of the cerebellum onbdth surfaces constitutes the poste-
rior lobe.
The roof of the rostral part of the fourth
ventricle is formed by the superior cerebellar
peduncles and by the superior medullary velum that bridges the interval between thern
(Fig. I0-2; see also Fig. 7-10). The remainder
of the roof consists of the thin inferior medullary velum, formed by pia mater and ependyma. This membrane, in which a deficiency
constitutes the median apefture of the fourth
ventricle or foramen of Magendie (see Fig.
I This,
despite its name, is the second fissure to appear
during embryonic development.
Chapter 10: Cerebellum
f65
tthis
r the
)-t).
fons
and
and
'su-
Hemisphere
the
ina
vell
:is
lres
tar,
red
he
Nodule
all
lat
Flocculus
I
I
Flo..ulo
nodular lobe
:e.
le-
Dorsolateral fissure
1y
m
Posterior lobe
S.
:d
al
Hemisphere
st
)-
il
:B
is
e
Figure lo'1. The cerebellum. (A) superior surface. (B) Inferior
( x 0.66)
surface.
h
I
6-4), commonly adheres to the inferiorvermis.
The three pairs of peduncles are attached to the
1
cerebellum
r
in the interval between the floc-
culonodular and anterior lobes.
Other fissures outline further subdivisions
or lobules, especially in the posterior lobe. The
names given to these lobules by ear\ anatomists have no functional significance; neither
is there uniform acceptance of a single system
of nomenclature, Figure I0-3 is provided for
reference, if smaller subdivisions of the cerebellum need to be identified. The position of
the tonsils is clinically significant
because
these parts of the cerebellar hemispheres are
close to the medulla and can compress this
vital paft of the brain stem if the contents of the
posterior fossa of the skull are displaced downward into the foramen magnum. The tonsil is
also an angiographic landmark, imparting a
characteristic curve to the course of the posterior inferior cerebellar artery.
Three functional divisions of the cerebellum are recognized, based on the destinations of different categories of afferent fibers.
Cortical histology is uniform throughout the
cerebellum, unlike the cerebral cortex, in
...'n
+
Anterior lobe
Lingula of vermis
showing through
the superior
medullary velum
w
Superior peduncle
TI
th
rh
Middle peduncle
Nodule
Flocculus
I
J
Flocculo-
nodular
th
c(
lobe
Inferior peduncle
c
Dorsolateral fissure
B
la
8:
Posterior lobe
is
Figure lo-2. The cerebeilum as viewed from in front
and below, showing the cut
surfaces of the cerebellar pedunct"r, n
i O"O'OI
VERMIS
H EMISPHERE
Central lobule
Anterior part of
quadrangular lobule
Posterior part of
quadrangular lobule
(simple lobule)
Culmen
Superior semilunar
lobule (crus I of
ansiform lobule)
Declive
Folium
Inferior semilunar lobule
(crus ll of ansiform lobule)
Biventral lobule
Superior semilunar
lobule (crus I of
ansiform lobule)
Inferior semilunar
lobule (crus ll of
ansiform lobule)
6.9.i5
Floccu lonodular
Nl
li.iiir:.i'.ljl lobe
[-_l
Anterior lobe
Posterior lobe
l-names of parts of the cerebellum. (The
drawings, is a small, flattened portion oi the
e central lobule and adherent to the superior
166
10_2).
rt
br
c
T
R
fc
o;
Chapter 10: Cerebellum
which there are histologically different areas.
The four central nuclei are likewise similar ar
the cellular level. The cortex and nuclei are,
therefore, described at this point, after which
the functional divisions and their individual
connections are discussed.
Cerebellar Cort
(Fig. l0-4). The
nje cell layer consists
of a single row ( sections) of bodies of purkinje cells,
are the principal cells of the
cerebellar cor
The molecular layer contains some
but is largely a synaptic zone, m
up of profusely branching dendrites of
cells and the axons of the
term molecular is derived
Because of the extensive folding of the cerebel-
lar Surface in the form of thin transverse folia,
85olo of the coftical surface is concealed. There
is, therefore, alatge cortical area, It is aboul
three-quarters as extensive as that of the cere-
bral cortex.
neurons, of which the most abundant are the
granule cells. The axons of these small inter_
neurons extend into the molecular laver.
Of the afferent fibers to the cortex, mossy
fibers terminate
Cortical Layers
Three ldyers are seen in histological sections.
hom the surface to the white matter of the
folium, these are the molecular layer, the layer
of Purkirle cells, and the granule cell layer
in synaptic contact with
granule cells of the innermost layer, whereas
ctimbing fibers enter the molecular laver and
wind among the dendrites of purkinje ceils. the
only libers that leave the cortex are axons of
Purkinje cells. These fibers terminate in central
nuclei of the cerebellum, with the exception of
some fibers from the cortex
of the
Molecular layer
Purkinje cell layer
Cranule cell layer
White matter
of folium
Figure l0'4. Transverse section of cerebellar folia showing the three
layers of the cortex and the underlying white matter. (stained-with ciesyl
violet, x 35)
floc-
167
f68
Regional Anatomy
ofthe Centtal Nervous
culonodular lobe that proceed
stem.
System
to the brain
re contacted by mossy
d axon enters the mofurcates and runs paral-
Cytoarchitecture
The five neuren types in the cerebellar cortex
establish a complex but remarkably regular
pattem of intracortical circuits. The precise
three-dimensional orientation of dendrites
and axons, as shown by the Golgi staining
method and by electron microscopy, has en_
at
ois
indicated in Figure lO-5.
Granule Celb and Mossg Fibers
The granule cells are small and closely packed
together in the deepest cortical layer. Each cell
has a spherical nucleuswith a coaise chromatin
pattern, and the scanty cytoplasm lacks clumps
ot Nissl substance. The short dendrites have
the cerebellum are mossy fibers that terminate
in synaptic relation wi
cells. While still in the
fiber dMdes into sever
enter the corto(
the granule celll
sheath and there
Alon
end,
as rosettes, with
whic
pakg
syn.ap_nc
contact.
t* #0fi:"i.;5;?l:
i
tion that includes the rosette of mossy"nUeq
{e1d1ite9 of granute cells, and tne axcin oia
qolgi cell (see Stellate and Golgi
Cells)
is known
Ba-basket
cetl
Go-Golgi
cetl
Purkinje
cell layer
Interneurons
Gr-granule
cell
P-Purkinje
Granule
cell layer
Climbing
fiber
To a central
nucleus of the
cerebellum
+
Excitatory synapse
-
Inhibitory synapse
Mossy
fiber
he cerebellar corto(, showing ercitatory and inhibitory
from Kieman JA: Introduction to Human Neuroscience,
19871
Chapter 10: Cerebellum
169
Cranule
cet
I
dendrite
Astrocyte
cytoplas,m
Axonal
rminal of
Colgi cell
Mossy fiber
rosette
Figure 10-6. Ultrastructure of a
synaptic glomerulus in the granule
cell layer.
(axonal terminal)
Mossy fiber
released by the presynaptic boutons, therebv
preventing diffusion to nearby glomeruli.
Purki4je Cells and Climbing Fbers
There a
hey
are
cell
easi
bodies.
c is
profuse dendritic branching in the molecular
layer, in a plane transverse to the folium. The
Basket Cells
The basket cells are scattered in the molecular
layer near the bodies of
furknje cells, The den_
drite of a basket cell branchesin the transverse
granule cells and the transverse orientation of
pect to
a
for a Pure number
ule cell to
contact many furkinje cells. The molecular
layer is, therefore, a rich synaptic field to which
stellate, basket, and Qolgi cells also contribute.
Axons of Purkinje cells traverse the granule
cell layer, acquire myelin sheaths, and terminate
mainly in central cerebellar nuclei. Collateral
branches given off by the axons synapse with
adjacent furkinje cells and with Golgi cells in the
outer part of the granule cell layer (see Fig,
10-5):
As the mossy fibers have a special relation-
Stellate and Golgi CeUs
Granule, furkinje, and basket cells have special
features, whereas stellate and Golgi celis are
similar to small neurons elsewhereln the nervous system,
lIl
.i
rl
J
rl
.l
']
170
Regional Anatomy of the
Centd
Neruous Srstem
potential
potential
mented
macolog
citatory transmitter is probably glutamate. All
the other cerebellar interneurons make inhibitory synapses, with gamma-aminobutyric acid
(CABA) as the probable transmitter. The excita-
tory input to the
intracortical circ
and therefore su
Figure l0-7. Cell body of a furkinje cellsituated between the molecular layer (aboue) and
the granule cell layer of the cerebellar cortex.
Most of the fibers surrounding the furkinje cell
body are preterminal branches of basket cell
€xons. (Cajal's silver nitrate method, x 450)
There are scattered stellate cells in the superficial part of the molecular laver whose dendrites are contacted by axons of granule cells.
Axons of stellate cells synapse mainly with furkinje cell dendrites; a few enter the innermost
cortical layer and establish a feedback circuit bv
synapsingwith granule cells. The Colgicells arb
situated in the outer portion of the granule cell
layer, and their dendrites extend into the molecular layer, where they are contacted by parallel fibers. Other afferents to Golgi cells are collateral branches of furkinie cell axons, Axons of
Colgicells enter glomeruli, where they synapse
with the dendrites of granule cells (see Fig.
10-6).
I ntracortical
Circuits
Recordings from microelectrodes inserted into
the cerebellar cortex have yielded information
about whether synapses between specific types
of neuron produce an excitatory postsyniptic
and the degree of er<citation resulting from an
incoming volley.
Aminergic Ftbers
Large numbers of noradrenergic axons enter
the cerebellum through its superior peduncle.
These unmyelinated fibers, which come from
the locus coeruleus, end bybranching profusely
in the molecular layer (see Fig. 1O-5). The noradrenaline released from these afferent fibers
may have a modulatory action at the synapses
between parallel fibers and furkinie cells. The
cerebellar cortqr also contains ro-e ,erotonergic axons from the raphe nuclei of the
n (see Ch. 9). lt has been sug-
drenaline and serotonin mav
ctions, the former amine enhancing and the latter reducing the excitatory
action of glutamate on the dendrites of furkinie
cells.
Central Nuc]ei
Four pairs of rruclei are embedded deep in the
medullary center; in a medial to lateral direction, they are the fastigial, globose, emboliform, and dentare nuclei (Fig. l0-S).
Chapter 10: Cerebellum
Fastigial nucleus
aptic
)ple,har-
and
eby
the
lory.
)ses
exAJI
ribi-
rcid
:ita-
by
llls,
iorers
.\\= :t'/
rlls,
:lls
,lgi
)ry
)(to
tje
he
_rd
(-/- -.'
o';o--::
\ .- V
Figure l0-8. Central nucleiof the cerebellum.
.,-
tn
The
er
e.
n
ly
fastigial nucleus
is nearly spherical,
close.to the midline, and almost in contact
with the roof of the fourth ventricle. The globose nucleus consists of two or three small
cellular masses, and the larger emboliform
's
nucleus is oval or plug-shaped. In mammals
as high in the phylogenetic scale as the mon-
e
key, a single nucleus (the nucleus interpositus
A
the fastigial and dentate nuclei. In apes and
B
or interposed nucleus) is situated between
humans, the interposed nucleus is represented
by the globose and emboliform nuclei. The
dentate nucleus is the most prominent of
the central nuclei; this mammalian nucleus is
Iargest in primates, especially in humans, The
dentate nucleus has the irregular shape of a
crumpled purse, similar to that of the inferior
olivary nucleus, with the hilus facing medially.
Its efferent fibers occupy the interior of the
nucleus and leave through the hilus.
The input to the cerebellar nuclei is from
(a) sources outside the cerebellum and (b) the
Purkinje cells of the cortex, The extrinsic input
consists of pontocerebellar, spinocerebellar,
and olivocerebellar fibers, together with fibers
from the precerebellar reticular nuclei. Most of
these
ffirents are collateral branches of fibers proto the cerebellar cortu. A few rubrocerebellar fibers end in the globose and emboliform nuclei, and the fastigial nucleus receives
afferents from the vestibular nerve and nuclei.
The fastigial nucleus discharges to the brain
stem through the inferior cerebellar peduncle,
whereas efferents from the other nuclei leave
the cerebellum through the superior peduncle
ceeding
and end in the brain stem and in the thalamus.
Results of physiological studies have indicated that the input to the central nuclei from
outside the cerebellum is excitatory, whereas
the input from Purkinje cells, which use GABA
as their transmitter substance, is inhibitorv.
Crudely processed information in the .ent.il
nuclei is re{ined by impulses received from the
cortex. The combination of the two inputs
maintains a tonic discharge from the central
nuclei to the brain stem and thalamus. This
l7l
Llz
Regional Anatomy
ofthe Central Nerlous
System
Figure l0-9. Midline structures of the brain stem and cerebellum, showing the
arb.or u.itae cerebelli in the vermis. The cut surface of the spe-imen has been
9$i1ed by a method that differentiates gray matter (dark'iand white matter
(ughA.
(x
u.
1.5)
al
rl
t(
discharge changes constantly according to the
afferent input to the cerebellum at any given
time.
at this point only as components of the cere-
bellar peduncles.
The
inferior cerebellar peduncle
con-
sists mainly of fibers entering the cerebellum,
;1r
i::
J
The white matter is scanty in tl^e region of the
vermis, where it produces a branching treelike pattern (the arbor vitae cerebelli) in a sagittal section (Fig. l0-9), Each hemisphere con-
tains a large medullary center in which the
dentate nucleus is embedded (Fig, I0-I0).
This white matter consists of afferent fibers to
the cortex, axons ofPurkinje cells proceeding
to the central nuclei, and efferent fibers of the
nuclei. The afferent and efferent systems are
discussed
in connection with the functional
divisions of the cerebellum, They are identified
with the largest contingent being of those that
originate in the contralateral inferior olivarv
complex of nuclei. The other components are
the dorsal spinocerebellar tract, cuneocerebellar fibers, fibers from the vestibular nerve and
nuclei, the arcuate nucleus,2 the nucleus of the
spinal trigeminal tract, the pontine trigeminal
nucleus, and the raphe and precerebellar retic-
g.
p
si
tI
p
fr
n
c
d
o
fl
e
2
The arcuate nucleus in the ventral part of the medulla
was briefly discussed in Chapter 7. It has afferent and
efferent connections similar to those of the pontine nuclei
and is probably a caudally displaced part ofthis neuronal
population.
I
1
T
Chapter
l0: Cerebellum
Li)
Figure l0-I0. cerebellar surface in a sagittal plane through a hemi,p"h"r", stained to differentiate gray matter.(dark) and white matter
in the white matter of
it'igirt).'fn" dentate nucleus is shown, embedded
the hemisphere.
(x
1'5)
I
ular nuclei. The inferior cerebellar peduncle
also contains efferent fibers that proceed from
the flocculonodular lobe and fastigial nucleus
to the vestibular nuclei and to the
central
group of reticular nuclei of the medulla and
DONS.
The
middle cerebellar peduncle
con-
in
cerebellar
superior
The
the pontine nuclei,
peduncle consists mainly of efferent fibers
irom the globose, emboliform, and dentate
sists of pontocerebellar fibers that originate
nuclei. The other fibers in the superior peduncles are afferent to the cerebellum' They include the ventral spinocerebellar tract on the
dorsolateral surface ofthe peduncle, fibers that
originate in the locus coeruleus, a few fibers
from the red nucleus, and fibers from the mesencephalic nucleus of the trigeminal nerve'
natfionlall A'ntatclnraY
Three divisions of the cerebellum are recognized on the basis of phylogeny (Fig' l0- I I ) '
The archicerebellum, which is the oniy
component of the cerebellum in fishes and in
Iower amphibians, consists of the flocculonodular lobe, together with a region of the
inferior vermis known as the uvula (see Fig'
l0-3). The paleocerebellum makes its flrst
appearance in higher amphibians and is Iarger
in reptiles and birds. In humans, it is represented by the superior vermis in the anterior
lobe and by part of the inferior vermis in the
posterior Iobe. The cerebellar hemispheres, together with the superior vermis in the poste-
rior lobe, constitute the neocerebellum,
which
is
found only in mammals and is largest
in humans.
These phylogenetic divisions of the cerebellum correspond in Iarge part with divisions
based on the major sources of afferent {ibers
(Fig, l0- l2). Thus the archicerebellumis identical to the vestibulocerebellum, which receives input from the vestibular nerve and nu-
clei. Those parts of the vermis that constitute
the paleocerebellum, together with the ad-
174
Regional Anatomy of the Central Neruous System
!
Nl
Archicerebellum
l-l
l0-ll.
Paleocerebellum
!
v"rtinrtocerebellum
l--l
Neocerebellum
N
Spino..rebellum
Pontocerebellum
Phylogenetic regions of the cer-
Figure 10-f2. Functional regions of the cere-
ebellum. (A) Superior surface. (B) Inferior sur-
bellum. (A) Superior surface. (B) lnferior sur-
face.
face.
jacent (neocerebellar) medial or paravermal
zones of the hemispheres, make up the spinocerebellum. This is the site of termination of
afferent fibers from these sources terminade in
the fastigial nucleus, which also receives collateral branchei of the axons destined for the
the spinocerebellar tracts and cuneocerebellar
fibers, which convey proprioceptive and other
sensory information, The remainder of the
cortex of the vestibulocerebellum. The cortex
and nucleus also receive afferents from the
accessory olivary nuclei,
Some Purkinje cell axons from the vestibulocerebellar cortex proceed to.the brain
stem (an exception to the general rule.that
such {ibers end in central nuclei), but most,
terminate in the fastigial nucleus. Fibers from
the cortex and the fastigial nucleus traverse
the medial portion of the inferior cerebellar
peduncle to their termination in the vestibular
nuclear complex and in the central group of
reticular nuclei. (One bundle of fastigiobulbar
Figure
neocerebellum (ie, the large lateral parts of
the hemispheres and the superior vermis in the
posterior lobe) constitutes the pontocere-
bellum.
The contralateralpontine nuclei send
afferent fibers to this area. There is some overIapping of the three divisions; for example,
some pontocerebellar fibers terminate in the
cortex of the spinocerebellum.
VESTIBULOCEREBEL
The vestibulocerebellum receives afferent fi-
fibers, known as the
bers from the vestibular ganglion and from the
vestibularnuclei of the same side (Fig. l0-13).
Russelll, has an aberrant course. The fasciculus crosses the midline, passes through the
other fastigial nucleus, and then curves over
the root of the superior cerebellar peduncle to
These enter the cerebellum in the medial part
of the inferior cerebellar peduncle. Some of the
uncinate fasciculus [of
Chapter
(To nuclei
t0: Cerebellum
of cranial nerves
Iil, tv, vt)
(To
sptno-
cerebellum)
r-l-'
I
I
Vestibular
ganglion
lnferior
olivary
Fastigial nucleus
Vestibulospinal
Cortex of flocculonodular Iobe
tract
(To spinal
cord)
Figure l0-13. connections of the vestibulocerebellum and
vestibular nuclei.
join other efferent fibers of the vestibulocere_
bellum in the contralateral inferior peduncle.)
In summary, the vestibulocerebellum in_
fluences motorneurons through the vestibulospinal tract, the medial longitudinal fasciculus,
and reticulospinal fibers. It is concemed with
adjustrnent of muscle tone in response to ves_
tibular stimuli. It coordinates the actions of
muscles that maintain equilibrium and partici_
in other motor responses to vestibular
stimulation (see Ch. 22).
pates
SPINOCBREBBLL
The following afferent systems project to the
spinocerebellar cortex. (a) The dorsal and ven_
tral spinocerebellar tracts convey data from
proprioceptive endings and from touch and
pressure receptors (Fig. l0_f4). The dorsal
tract, consisting of the axons of the neurons
constitutingthe nucleus thoracicus in spinal
segments Tl to L3 or L4, conveys information
from the trunk and leg, The ventral tract,
which arises in various parts of the lum_
bosacral gray matter (see Ch. 5), is involved
mainly in conduction from the leg. (b) Cune-
ocerebellar fibers from the aciessory cuneate nucleus (see Ch. 7) are equivalent, for
the arm and neck, to those of ttre dorsal spi_
nocerebellar tract, Most of the fibers afferenito
the cells of origin of the spinocerebellar and
cuneocerebellar tracts have ascended in the
dorsal funiculi of the spinal cord.
l7S
176
Regional Anatorny
ofthe Central
Nervous System
Posterior division
of ventral lateral
nucleus of
se.
ve
thalamus
m,
Pontine
reticu lotegmental
SU
Reticular formation
(central group
nucleus
is
of nuclei)
ac
m
et
Lateral and
paramedian
AI
reticular nuclei
Clobose
di
and
emboliformnuclei
Contralateral
ve
inferior
c€
olivaru
complex
fa
th
rt
$r
tc
bt
til
el
Fastigial
br
ol
D'
nucteu5
br
Vestibular
nuclei
r(
Dorsal and ventral
spinocerebel lar,
cuneocerebella4 and
Reticulospinal
Vestibulospinal
tract
tract
trigeminocerebeilar
tracts
Figure 10-14. Connections of the spinocerebellum.
fi
gi
b
e:
n
li
p
p
c
Data from cutaneous receptors are carried
by spinoreticular fibers to the lateral and
par:rmedian reticular nuclei (see Figs. 9_t
and9-2) , from which fibers project ro thi cere_
bellum. These two nuclei also receive afferenr
fibers from primary motor and sensory areas
of
the cerebral cortex. Another precerebellar reticular nucleus that projects to the vermis and
medial pafis of the hemispheres is the re-
ticulotegmental nucleus in the pons
(see
Fig. 9-1). This nucleus receives afferents from
the cerebral cortex and from the vestibular
nuclei. Finally, the spinocerebellum receives
fibers from all three trigeminal sensory
nerve and from the accessory olivary nuclei
(in which spino -olivary tracts terminate ). CoIlateral branches of the axons from the various
afferent sources terminate in the globose and
emboliform nuclei, which also receive a small
contingent of fibers from the red nucleus.
Each half of the body is represented in the
ipsilateral cerebellar cortex; if afferent fibers
t
tl
T
d
r
ir
c
T
L
t
t
I
t
Chapter 10: Cerebellum
sented in two areas: one in and alongside the
vermis inthe anteriorlobe, andthe otherinthe
medial part of the hemisphere on the inferior
sur{ace of the posterior lobe. The ,,head area,,
is in the superior vermis and the immediatelv
adjacent cortex of the posterior lobe. So_
matotopic representation in the spinocer_
ebellum is less clearly defined than ln some
areas ofthe cerebral cortex; there is overlap of
different inputs, so that ffains of impulses from
various sources may reach the same purkinje
cell.
area of the cerebral cortex. The end result is
conuol of muscle tone and synergy of collab_
orating muscles, as appropriate at any mo_
ment for the adjustment of posture and in
many types of movement, including those of
locomotion,
PO
CBREBELLUM
Pontocerebellar fibers constitute the whole of
rS,
lei
the vermis of the anterior and port.rio, tolll
and throughout the cortex of the cerebellar
hemispheres. The large lateral regions of the
hemispheres constitute the pontocerebellum.
tonus are effected
bulbar connections
tibiilocerebellum, F
emboliform nuclei traverse the superior cere_
bellar peduncle and terminate in the central
group of reticular nuclei. Thus the spinocerebellum may influence motor neurons through
reticulospinal fibers and a similar projection to
motor nuclei of cranial nerves. Alpha and
garnma motor neurons are involved in cere_
bellar control of muscle action, and the influence of the spinocerebellum on the skeletal
musculature is ipsilateral.
Some fibers from the globose and embo_
liform nuclei traverse the superior cerebellar
peduncle a4d end in the red nucleus. Others
pass through or around the red,nucleus and
continue to the ventral lateral nucleus of
the thalamus, from which fibers project to
the primary motor area of the cerebral cortex,
The main projection of the red nucleus is
through the central tegmental tractto the inferior olivary complex of nuclei.
In summary, the spinocerebellum receives
information from proprioceptive and exteroceptive endings and from the cerebral cortex.
These data are processed in the circuitrv of the
cerebellar cortex, which modifies and refines
the discharge of nerve impulses from the central nuclei. Motor neurons are inlluenced
mainly through relays in the vestibular nuclei,
the reticular formation, and the primary motor
Through corticopontine tracts that origi_
nate in widespread areas of the contralateial
cerebral cortex (especially that of the frontal
and p4rietal lobes) and the pontocerebellar
projection, the cortex of a cerebellar hemi_
receive afferents from the superior colliculus
and relay data used by the cerebellum in the
control of visually guided movements.
Purkinje cell axons from the pontocerebellar cortex terminate in the dentate nucleus,
the efferent fibers of which compose most of
the superior cerebellar peduncle. After travers_
ing the decussation of the peduncles, some den-
tatothalamic fibers give off collateral branches
that go to the red nucleus and the inferior
olivary complex, but the great majority pass
through or around the red nucleus andind
in the ventral lateral nucleus of the
thalamus. This thalamic nucleus projects in
tum to the primary motor area of cortex in the
frontal lobe. Through these connections. the
ify activity in corand reticulospinal
The output of the dentate nucleus, like that
of the other cerebellar nuclei, fluctuates ac_
cording to the excitatory input from extra_
cerebellar sources and the refinement of dis_
charge by the inhibitory action of purkiqje
cells. Main_ly through its inlluence on the cere_
177
178
Reglonal Ailqtotny of the cenffal Neruous system
pont
Cerebral cortex (f rontal,
parietal, and temporal Iobes)
wher
the
cort€
fastil
vary
affer
from
ipsili
Ventral lateral
nucleus of
T
thalamus
vary
(posterior division)
relat
perf(
cern
Red nucleus
ass
syna
TETS
Central tegmental tract
Cortex of
cerebellar
hemisphere
I
fiber
sitio
fiber
exec
mer
ferer
are
Pontine
nuclei
mor
neu'
ceiv
nuc
tho:
toc€
lnferior
olivary
the
keyr
Dentate nucleus
comptex
reac
thrc
tine
Figure 10-15. Connections of the Pontocerebellum.
dorr
acot
con
bral motor cortex, the pontocerebellum en-
licu
sures a smooth and orderly sequence of muscle
contractions and the intended precision in the
force, direction, and extent of volitional movements. These functions are particularly important for the upper limb. A cerebellar hemisphere influences the musculature of the same
side of the body because of the compensating
decussations of the superior cerebellar peduncles and of the corticospinal tracts and other
descending pathways.
There is
a
large contingent of
olivocerebellar
fibers from the inferior olivary nucleus and
from the dorsal and medial accessory olivary
nuclei in the medulla. These cross the midline
and enter the contralateral inferior cerebellar
peduncle to be distributed to all parts of the
cerebellar cortex. Olivocerebellar fibers also
end in cerebellar nuclei. The principal inferior
olivary nucleus projects to the cortex of the
are
*rr(
visr
corl
tha
fur
cal
pro
Chapter
pontocerebe
whereas the
the
spinoce
cortex and to the emboliform, globose, and
fastigial nuclei. In addition to tlie rubro-oli_
vary fibers indicated in Figure I 0 - I 5 , the main
afferents to the inferior olivary nucleus are
from the sensorimotor strip of cortex of the
ipsilateral cerebral hemisphere (see Ch. 7),
The climbing fibers from the inferior oli-
)0: Cerebellum
lary, and urinary bladder responses, They are
sympathetic in nature when the anterioilobe
is stimulated and parasympathetic when the
tonsils (see Fig. f 0-3) of the posterior lobe are
stimulated. The postulated pathway includes
the interposed nuclei, reticular formation and
hypothalamus.
Cerebellar Disorders
Pathological conditions are classified broadlv
into those that affect the vermis and flocculo_
nodular lobe (the vestibulocerebellum and
spinocerebellum) and those that affect the
synapseS,
It has been suggested that transmit_
hemispheres (pontocerebellum),
MIDLI
execution and coordination of learned move_
ments are mediated by the mossy fiber af_
ferents, of which those from the poniine nuclei
are the most numerous in primates. When a
monkey makes an intended movement, the
neurons in the dentate nucleus (which receives its excitatory afferents from the pontine
nuclei) are active several millisecondi before
those in the primary motor area.
to
th
dorsal region
LESIONS
vermis. The patient has an unsteady, stagger_
ing ataxic gait, walks on a wide base, ana
sways from side to side. Cerebellar nystag-
mus is "pendular,,, with .y"
-ou.-.nts of
equal
speed in both directions, usually in the
horizontal plane, It is attributed to interrup_
tion of connections of the vermis with the ocu_
lar motor nuclei by way of the vestibular nuclei
of the pontine nuclei
convev
acoustic data as well as visual data because of
i
connection from the inferior to the superior col_
liculus. Stimuli perceived by the eyei and ears
are also able
to influence the cerebellum
through cofiicopontine Iibers that originate in
visual and auditory areas of the cerebral
cortex.
Results of animal experiments have shown
that the cerebellum also has a role in visceral
functions. Under certain conditions, electri_
cal stimulation of the spinocerebellar cortex
produces respiratory, cardiovascular, pupil-
With re
signs
of
intemrp
i.sjllli,'j;
destruction
of the cortex and medullary center, or involve
the central nuclei or the efferent pathways in
the superior cerebellar peduncle. the motor
disorder is seve
lesion involves
rior cerebellar
unilateral, the signs of motor dysfunction are
on the same side of the body.
l7g
180
Regional Anatorny of the Central Nervous Systeffi
The following signs, in varying degrees of
severity, are those of a neocerebellar syndrome. Movements are ataxic (intermittent
or jerky). There is dysmetria; for example,
when the patient reaches out with the Iinger to
an object, the finger overshoots the mark or
deviates from it (past-pointing). Rapidly altemating movements, such as flexion and extension of the fingers or pronation and supination of the forearm, are performed in a clumsy
manner (adiadochokinesis), Asynergy is
separation of smoothly flowing voluntary
movements into successions of mechanical or
puppet-like movements (decomposition of
movement). There may be hypotonia of
muscles, which also tire easily. Cerebellar
tremor, which occurs most frequently with
'
demyelinating lesions in the cerebellar peduncles, usually occurs at the end of a particular
movement (intention tremor). Dysarthria
is evident if asynergy involves muscles used in
speech, which is then thick and monotonous
(sluning; scanning speech). There may be
nystagmus/ if the lesion encroaches on the
vermis. The deficits noted are superimposed
on volitional movements that are themselves
basicallv intact.
SUGGESTED READING
Brooks VB: The Neural Basis of Motor Control. New
York, Oxford University Press, 1986
Decety J, Sjoholm H, Ryding E, Stenberg G, Ingvar
DH: The cerebellum participates in mental ac-
tivity: Tomographic measurements of regional
cerebral blood flow, Brain Res 5i5t3l3-3l7,
1990
FitzGerald MJT: Neuroanatomy Basic and Clinica-.
2nd ed, London. Ballidre Tindall, 1992
Lalonder R, Botez MI: The cerebellum an! leaming
processes
in animals. Brain Res nev tf
)32, L990
:lZl-
Llin6s RR, Walton KD: Cerebellum. In Shepherd
GM (ed): The Synaptic Organization of the
Brain, 3rd ed., pp. 214-245. New york, Oxford
University Press, 1990
Tledici G, Barajon I, Pizziti G, Sanguineti I: The
organization of corticopontine fibres in man.
Acta Anat 137:320-32), t99O
Walton J: Introduction to Clinical Neuroscience,
2nd ed. London, Ballidre Ttndall. 1987