Studies in the Osteopathic
The Nerve Centers: Volume
Louisa Burns, M.S., D.O., D.Sc.O.
The cerebellum together with the pons represents the full development of
the metencephalon. It is a fair representative of the complexity
of relationship which characterizes those nerve centers whose functions
have been subject to changes during their phylogenetic development.
the lowest vertebrates the metencephalon consists of a segment scarcely
more differentiated than is any other segment of the neural axis.
A prolongation from the lateral aspect of the metencephalon represents
the beginning of a cerebellum. It receives, at first, only the terminals
or collaterals from those sensory cells of the second order which receive
the impulses from the lateral line sensory organs. (These organs,
it should be remembered, are represented in the adult mammal only by certain
of the structures of the middle ear.) In fishes of a somewhat higher
order the cerebellum receives also terminals and collaterals from the secondary
gustatory nucleus. Later, the fibers from the mesencephalic nuclei,
concerned in the reception of impulses of sight and hearing, and from the
gracile and cuneate nuclei, concerned in the reception of the sensory impulses
from the body tissues, are received. The ascending cerebellar fasciculi
are of more recent origin. Among fishes the cerebellum is very well
developed, especially in the direction of the coordination of the sensory
impulses. The life habits of fishes require this delicate coordination
in order that they may retain their position while floating in a medium
of about the same specific gravity as their own bodies.
the beginning of the land habits in amphibia the cerebellum becomes a less
conspicuous object in the nervous system. The disappearance of the
lateral line organs causes a large part of the nerve fibers to the cerebellum
to be lost. With the more exact vision and the more need for reactions
to answer speedily the stimulation received from a single sense organ,
the need for wide coordination of sensory impulses becomes superseded by
the need for a more exact coordination of efferent impulses. Thus
it happens that we have the appearance of an organ of great efficiency
in one class of vertebrates, becoming of less importance in another, and
later reaching an efficiency along slightly different lines, far surpassing
the primitive development.
the lower amphibians to man the development of the cerebellum has progressed
in the direction of increasing the coordination of the efferent rather
than the afferent impulses. This end is secured, in part, by means
of the very wide sensory connections, the foundation for which was laid
in the fish cerebellum, in part by the development of more distant sensory
connections, and in part by the development of other connections with higher
centers, and by the increasing complexity of the relations of all of these.
structure of the cells of the cerebellum itself has changed comparatively
little. The axons of the Purkinje cells remain the sole efferent
path of impulses from the cerebellar cortex. The incoming impulses,
whether from sensory nuclei, lower centers, midbrain, or the cerebral cortex
itself, are, so far as our present knowledge can say, limited to the primitive
simple methods of receiving; the incoming fibers either terminate in brushlike
endings in connection with the brushlike endings of the granule dendrites,
or they exhaust themselves by fine branchings, which apply themselves to
the dendrites of the Purkinje cells. It is not possible to localize
the fibers from the different parts of the nervous system in the cerebellum
with any exactness.
Fig. 53. Cells from the cerebellum of
half-grown kitten. A – Granular layers. B – Molecular layer.
Fig. 54. Purkinje cell from cerebellum
of man 63 years old. 175 diameters.
Fig. 55. Section across cerebellar convolution,
adult woman. Semidiagrammatic. 72 diameters.
Fig. 56. Longitudinal section through
cerebellar convolution, adult woman. Semidiagrammatic. 72 diameters.
histological structure of the cerebellum is as complex as its phylogenetic
development would indicate.
cortex presents two layers, between which lie the bodies of the Purkinje
cells. These cells are sometimes classified as a third, or ganglionic
outer or molecular layer is so called from the presence of a number of
very small nerve cells. (Fig. 53.) The cells of the outermost
part of this layer are very small multipolar cells, whose axons exhaust
themselves by repeated branchings in the immediate neighborhood of the
cell body. They are a form of the Golgi Type II cells. In the
deeper part of the molecular layer are found the stellate or basket cells.
These are of stellate form, multipolar, with freely branching dendrites.
Their axons pass along the deeper part of the molecular layer, in a direction
parallel with the direction of the folds of the cerebellar cortex.
Thus, in order to secure sections showing these axons it is necessary to
cut the convolutions of the cerebellum longitudinally. (Fig. 56)
From these axons collaterals are given off, which descend to the bodies
of the Purkinje cells and break up into a feltwork of fibrillae, which
make a basket around the bottle-shaped bodies of the Purkinjes. (Fig.
18.) The number of collaterals from any given axon of the basket
cell seems to be very large. (I have seen seven collaterals from
one such axon in one section of Golgi material.)
molecular layer contains a very large number of nerve fibers. These
include the following:
from the small granules of the granular layer pass through the molecular
layer to the periphery, divide in a T-shaped manner, and pass tangentially
along the cortex. From these branching axons collaterals descend
into the molecular layer to form synapses with the nerve cells therein.
dendrites of the Purkinje cells branch freely among the cells of the molecular
layer. The axons of the Purkinje cells give off collaterals, which
pass toward the cerebellar cortex through the molecular layer, and form
synapses with the multipolar cells. In the molecular layer are also
the climbing fibers of the cerebellum.
middle or ganglionic layer, as it is sometimes called, is composed of the
bodies of the Purkinje cells. (Fig. 54.) These are large and
bottle-shaped, and their bodies are closely invested by the basketlike
branchings of the collaterals of the axons of the stellate or basket cells
of the molecular layer. The dendrites of the Purkinje cells are characteristic.
They branch very freely in one plane without the molecular layer.
The dendrites are beautifully tree-shaped, and the whole cell presents
a very striking appearance in sections prepared after the method of Golgi.
The plane of division of the dendrites is placed at right angles to the
direction of the convolutions, so that if one wishes sections showing the
dendrites of the Purkinje cells, it is necessary to cut the convolutions
crosswise. (Fig. 55.) The dendrites of the Purkinje cells are
closely followed by the branchings of the climbing fibers.
inner granular layer is so called from the appearance of its most abundant
cells. These are called granules, and include two classes, large
and small granules. The granule cells are alike in form. They
are multipolar, and their dendrites terminate in peculiar, brushlike end
tufts. (Fig. 53.) These end tufts are in close relationship
with the similar brushlike terminations of the collaterals and terminals
of the moss fibers of the cerebellum. The small granule cells have
long axons, which penetrate the molecular layer, branch in a T-shaped manner,
and run tangentially along the cortex, giving off collaterals to the cells
of the molecular layer at intervals. The large granules are of the
Golgi Type II class. Their axons exhaust themselves by repeated branchings
among the dendrites and axons of their immediate neighborhood.
the granular layer the axons of the Purkinje cells pass as they leave the
cortex; through this layer also the collaterals from these axons pass toward
the cortex. The entering climbing and moss fibers penetrate this
layer in reaching their destination.
the granular layer is found the cerebellar medulla of white fibers passing
to and from the cortex. These fibers are supported by neuroglia cells.
white matter includes fibers of two classes, neither of which is as well
known as is desirable.
climbing fibers enter the cerebellum, but their origin is not certainly
known. They probably enter by way of the restiform body or the branchium
pontis. They pass to the cortex, branch freely, and apply themselves
to the dendrites of the Purkinje cells, which they follow to their ultimate
moss fibers enter the cerebellum, but their origin is not known.
They branch freely, and their collaterals and probably also their terminals
break up into the brushlike end tufts already described for the granule
cell dendrites, and closely applied to them.
axons of the Purkinje cells pass downward through the white matter, and
they alone are corticifugal. It is not certainly known whether most
of the Purkinje cells terminate in the dentate nucleus, or whether most
of them leave the cerebellum. Part of them certainly stop in the
it is remembered that the dendrites of the Purkinje cells branch widely
in a plane at right angles to the direction of the convolutions, that these
widely-branching dendrites are thoroughly permeated with the collaterals
and axons of the multipolar cells of the molecular layer, with the tangential
fibers of the axons of the small granular cells, and with the axons of
Golgi Type II cells; when it is remembered also that the axons of the stellate
cells pass parallel with the direction of the convolutions, and thus at
right angles to the direction of the Purkinje dendritic plane, and that
a considerable number of Purkinje cells may receive the basketlike terminations
of any one stellate axon, then the complexity of this structure may in
part be realized. The recurrent collaterals of the Purkinje axons
add to the intricacy of the arrangement.
Fig. 57. Section through nucleus dentatus,
adult woman. 10 diameters.
Fig. 58. Cells of nucleus dentatus from
same section as Figure 57. 800 diameters.
masses of gray matter centrally placed require much more study. The
nucleus dentatus is the largest of these masses. It is found in the
lower animals as a single mass of gray matter of simple form. In
the human cerebellum it presents the characteristic dentate appearance,
very much like that of the olive. Its phylogenetic development is
not known. It may represent an infolding of the cerebellar cortex.
(Figs. 57, 58.)
nucleus emboliformis is placed at the hilum of the dentatus, like a cork
for that structure. The globosus lies mesially from the emboliformis.
These nuclei present some evidence of being of phylogenetic descent from
the secondary gustatory nucleus of fishes. The fibers of the anterior
ascending cerebellar fasciculus pass into these nuclei, but whether the
axons terminate in part or as a tract, or whether they pass without relay
to the cortex, is not certainly known.
nucleus tectis lies in the roof of the V-shaped ventricle. It seems
to represent an infolding of the cortex.
cerebellum receives nerve impulses from very nearly all parts of the central
nervous system, and since this includes all or practically all of the sensory
neurons, both visceral and somatic, it follows that the cerebellum receives
impulses from the entire body.
connections of the cerebellum are as follows:
Somatic sensory neurons of the first order may send axons or collaterals
to the superior vermis by way of the restiform body. This includes
the fibers of the fasciculus gracilia and fasciculus cuneatus, which pass
into the restiform body without relay, and the fibers of cranial sensory
nerves, which may follow the same path.
Visceral sensory neurons of the first order may send axons or collaterals
to the cerebellum by way of the restiform body. Probably these include
very few fibers.
Somatic sensory neurons of the second order send many axons and collaterals
to the cerebellum, chiefly by way of the restiform body from the nucleus
gracilis, nucleus cuneatus and the cranial nerve nuclei of termination.
These seem to reach the cortex of the superior vermis.
Visceral sensory neurons of the second order send many axons to the superior
vermis cortex. These include the fibers of the anterior ascending
cerebellar fasciculus (direct cerebellar), which passes by the restiform
body, and a part of the posterior ascending cerebellar fasciculus (Gower’s
tract), which passes through the medulla and pons and send some fibers
by the brachium conjunctivum (superior peduncle) into the cerebellum.
Axons or collaterals from the nucleus pontis pass to the cortex of the
hemispheres of the cerebellum. For the most part these axons pass
to the contra-lateral hemisphere, but a few of them pass to the hemisphere
of the same side.
Axons of cells of the red nucleus have been said to enter the cerebellum
by way of the brachium conjunctivum. This connection has been doubted
by later studies. It seems probably that a small number of fibers
form the red nucleus to the cerebellum pass by way of a bundle in the brachium
The cells of the olive send axons to the cerebellum, but whether to the
dentate nucleus or to the cortex is not known.
cerebellum sends impulses by almost as varied pathways.
The axons from the cells of the nucleus dentatus make up the larger part,
if not all, of the brachium conjunctivum (superior peduncle). These
axons terminate for the most part, in the red nucleus, but also in part
in the quadrigeminates and the optic thalamus. The brachium conjunctivum
fibers decussate immediately after emerging from the cerebellum.
These fibers probably carry impulses concerned in consciousness of heat,
cold, pain, muscular effort and the various visceral sensations.
Axons from the cells of the cortex of the cerebellar hemispheres pass by
way of the brachium pontis (middle peduncle) to the nucleus pontis, mostly
contra-lateral, but partly to the same side.
Descending axons either from the cortex (the Purkinje cells) or from the
dentate nucleus pass downward through the cord, forming synapses with the
cells of the central and postero-lateral gray matter, and through them
affecting the activity of the cells of the anterior and the lateral horns
of the cord.
Axons from either the cortex or the dentate nucleus pass by way of the
restiform bodies to the olive, the medullary centers, and the motor cranial
nerve nuclei. Very little is known of the various relationships.
Functions of the Cerebellum
The functions of the cerebellum have been the subject of much study.
Experimental evidence is almost as much at variance with clinic evidence
as the different manifestations of clinic evidence vary among themselves.
It seems to be well proved that the cerebellum is chiefly concerned in
the maintenance of the tome of the visceral and somatic muscles, the maintenance
of the tome of the visceral and somatic muscles, the maintenance of equilibrium,
the coordination of complex movements, and with the transmission of visceral
and certain common somatic sensations to the cortex. These functions
are of great importance, yet widespread disease of the cerebellum may be
associated with few or no localizing symptoms. In the presence of
tumors or other lesions involving the cerebellar hemispheres it is rare
for a diagnosis to be made ante-mortem unless the peduncles are involved.
Lesions of the vermis are sometimes recognized, but it sometimes
happens that even vermis lesions escape recognition until postmortem.
of the cerebellar hemispheres in the anesthetized animal produces no perceptible
effects. Stimulation of the central gray matter may be followed by
contraction of the muscles, chiefly those of extension of the same side
of the body, if the basal ganglia remain intact. Section of the brachium
conjunctivum precludes this reaction. Stimulation of the brachium
pontis is followed by contraction of the muscles, chiefly those of extension
of the same side of the body. These movements include the diaphragm
and the intercostals. No visceral effects have been seen to follow
any stimulation of the cerebellar tissues. Stimulation of the restiform
body produces no perceptible effects.
of the cerebellum are rather rare and are not always to be recognized.
The gross lesions include those found in any other part of the brain—abscesses,
gummata, tubercles, etc., and the symptoms produced are often not very
well related to the normal functions of the cerebellum, as indicated by
its structural relationships.
removal or injury of a considerable part of the cerebellum is followed
by a loss of muscular power and of coordination on the same side of the
body. There is no perceptible loss of sensation. There may
be or may not be muscular tremors and athetosis. If the injury is
not progressive, and the subject is not too old, there is later produced
some effort at compensation, either upon the part of the cerebellum left
intact, or by other centers capable of coordinating the impulses concerned
in producing the complex actions of the skeletal muscles. No symptoms referable
to an injury of the viscero-sensory paths have been described in cerebellar
as one of the nerve centers, must depend for its normal activity upon the same
conditions which affect the other nerve centers; that is, the cerebellum depends
for its food supply upon the blood brought to it. This blood must be good,
clean, and kept rapidly flowing if the cerebellar cells are to maintain their
proper activity. This activity also depends upon the receipt of certain
impulses from the other parts of the nervous system already described.
In the lack of these impulses, or if they should be rendered abnormal in any
way, the normal coordinations are not found. It is doubtless true that
many of the mistakes made by weary people, or by people whose bodies are in
any way subnormal, may be due to one of two conditions—either the cerebellar
cells are poorly nourished and are thus inefficient, or the nerves carrying
sensory impulses, or other impulses, to the cerebellum are not such as to lay
the foundation for normal coordinating activities in the cerebellar cells.
It is by means of this relation that many of the accidents called “careless”
are produced by persons who are neurotic or poorly nourished, or whose nerve
cells have a lower liminal value than usual for any reason. During childhood
the progressive development of the neurons concerned in the higher unconscious
coordinations may be associated with periods of poor coordinations. Children
at this age are, no doubt, often blamed for the awkwardness and carelessness,
due, in large part, to the delayed or unbalanced development of the cerebellar
neurons, or of the neurons upon whose activity the coordinations depend.