Bulbar Structures Concerned in Primitive
Movements
Certain deductions may be made about the
various structures in the bulb and hypothalamus
concerned in primitive movements. The pig mented
cells of the substantia nigra and reticular
formation of the pons and medulla function as
vital centres controlling respiratory
activity.
The connections of the substantia nigra in
primates resemble those in the lower mammals.
The nucleus receives afferents from the tectum,
globus pallidus, corpus Luysii, lateral
lemniscus and the mammillary bodies and both
discharges into the reticular formation of the
pons and medulla in relation to the dorsal
nucleus of the vagus and also into the red
nucleus. Trough the afferents from the tectum
respiratory activity may be correlated with the
primitive movements mediated through the tectal
region, in which lies the centre for reflex
vocalisation. Through the fibres it receives in
the lateral lemniscus respiratory activity is
correlated with reflex movments to sound.
Through the fibres from the mammifiary body
the cells of the nucleus receive their
controlling adrenergic fibres. Through the
fibres from the globus pallidus and corpus
Luysii respiratory activity may be correlated
with other activities mediated by these two
nuclei. Swallowing movements are dependent on
structures beneath the floor of the fourth
ventricle in the region of the vagus nucleus and
stimulation in this region simultaneously causes
swallowing and inhibits respiratory movements
(Millet and Sherrington 1915-6).
Presumably involuntary opening of the mouth
and chewing movements also depend on the
integrity of the same area. It seems that the
movements must depend on the local reticular
structures. The afferent fibres concerned in
this complex reflex reach this part of the bulb
in the trigeminal, glossopharyngeal and vagus
nerves.
Yawning still occurs after bilateral
motor decortication in man or in decorticate
lower mammals. In the former it is completely
uncontrollable, as it may be in normal subjects.
Yawning not only involves a wide opening
of the mouth, but is preceded by a deep
inspiration. The eyes often close and the act is
often followed by pilo-erection and shivering.
In biteral motor decorticate man yawning
is accompanied by gross moves of the large
joints (associated movements).
Curious attacks of yawning and
respiratory disturbance may follow an attack of
encephalitis lethargica, which especially
damages the hypothalamus and the region of the
substantia nigra. Yawning would thus
appear to depend on the structures in the bulb
or hypothalamus and to be closely related
respiratory activity.
It occurs :
(1) In states of tiredness and sleepiness,
in which there is a depression of adrenergic and
an increase of trophic cholinergic activity
throughout the brain.
(2) In conditions of excessive heat, when
there is a general increase of cholinergic
activity in the body and sleepiness.
(3) During anxiety, when a similar general
stimulation of trophic and autonomic functions
occurs.
(4) During the induction of amesthesia with
barbituates, which depress adrenergic activity
and induce sleep.
(5) In animals in states of anaphylactic
shock, when the initial stimulation of all
trophic and autonomie is followed by a
depression of adrenergic activity.
(6) During boredom, when adrenergic activity
is deficient.
Yawning thus occurs when there is a
general increase of trophic cholinergic activity
within the nervous system and thus when
respiratory activity is diminished and anoxia
tends to develop. Since general stimulation of
adrenergic activity in the body increases the
depth of respiration, the deep inspiration which
precedes a yawn, and the pilo-erection
and shivering, which follow indicate an
increased adrenergic activity. This seems to be
an attempt to increase the oxygenation of the
blood by stimulation of the respiratory centres.
The excitation of the structures in the
reticular formation initiated by the activity of
the substantia nigra apparently spreads to
neighbouring nuclei and induces opening of the
jaws and the primitive slight movements of the
large joints occurring in bilateral motor
decorticate man.
Le
syndrome de Wyburn-Mason ou de
Bonnet-Dechaume-Blanc comprend l'association de
malformations artério-veineuses du
maxillaire, de la rétine, du nerf
optique, du thalamus, de l'hypothalamus et du
cortex cérébral. La
prévalence du syndrome n'est pas connue
mais il est très rare : moins de 100 cas
ont été publiés à ce
jour.
Wyburn-Mason
syndrome is characterized by the association
of arteriovenous malformations with a metameric
topography located in the facial and
ocular-orbital regions or involving the central
nervous system. The syndrome is very rare with
about 100 cases reported in the literature so
far.
