DISEASES OF THE NERVOUS SYSTEM
GENERAL DISCUSSION.--The nervous system may be divided into central and
peripheral portions. The _central portion_ comprises the brain or
encephalon and the spinal cord. These organs are lodged in the cranial
cavity and spinal canal. The nerves and ganglia comprise the _peripheral
portion_. The nerves form white cords that are made up of nerve fibres. The
ganglia are grayish enlargements formed by nerve cells and supporting
tissue, situated at the origin of the nerve trunk or along its course.
_The brain_ is an oval mass of nerve tissue elongated from before to
behind, and slightly depressed from above to below. It terminates
posteriorly in the spinal cord. It is divided into three portions:
_cerebrum, isthmus_ and _cerebellum_ (Fig. 25).
_The cerebrum_ forms the anterior portion. It is divided into two lateral
lobes or hemispheres by a deep longitudinal fissure. The surface of the
cerebral hemispheres is gray and roughened by pleats or folds separated by
grooves or fissures. The gray or cortical layer is distinct from the white
or connecting structure. The cortical layer is made up of nerve cells or
areas which control the voluntary muscles of the body. It is connected with
the special senses of touch, temperature and muscle-sense. The gray layer
is connected with the posterior portion of the brain, the isthmus or
medulla oblongata, by the white nerve tissue.
_The isthmus_ or _medulla oblongata_ is elongated from before to behind and
connects the cerebral hemispheres with the spinal cord, anteriorly and
posteriorly. It is divided into several different portions, and is made up
largely of white connecting fibres with nuclei of gray matter scattered
through them. The isthmus is hollowed out by a system of small ventricles
that extend from the cerebral hemispheres to the spinal cord, where they
terminate in a small, central canal. The isthmus is the highway between the
spinal cord and the higher nerve centres. It has in it certain cell centres
that give origin to six of the cranial nerves.
[Illustration: FIG. 25.--Photograph of model of horse's brain: longitudinal
section; lateral view; cerebrum; cerebellum; and isthmus.]
The third division of the brain is the _cerebellum_. This is a single mass
supported by the isthmus. It is situated posterior to the cerebrum, from
which it is separated by a transverse fold of the membranes covering the
brain. This mass of nerve tissue is much smaller than the cerebrum. The
white nerve tissue forms central nuclei which send out branches that ramify
in every direction. The centre of the muscular sense is said to be located
in this division of the brain. A second function is the maintenance of body
equilibrium through its connection with the nerve of the middle ear.
_The spinal cord_ commences at the posterior opening (occipital foramen) of
the cranial cavity, and terminates posteriorly in the lumbar region at the
upper third of that portion of the spinal canal belonging to the sacrum. It
is thick, white in color, irregularly cylindrical in shape, slightly
flattened above and below and reaches its largest diameter in the lower
cervical and lumbar regions. The spinal canal is lined by the outer
membrane that envelops the cord, which aids in fixing this organ to the
wall of the canal. The spinal cord is formed by white and gray nerve
tissue. The gray tissue is situated within the white, and it is arranged in
the form of two lateral comma-shaped columns connected by a narrow
commissure of gray matter. The extremities of the lateral gray columns mark
the origin of the superior and inferior roots of the spinal nerves. The
white tissue of the cord is also divided into lateral portions by superior
and median fissures. The inferior fissure does not extend as far as the
gray commissure, leaving the lateral inferior columns connected by a white
commissure. There are certain centres in the spinal cord that are capable
of carrying on certain reflex actions independent of the chief centre in
the brain. The white matter of the cord is made up of paths over which
impulses to and from the brain are transmitted.
_There are twelve pairs of cranial nerves_. Two pairs belong exclusively to
the special senses, smell and sight. Altogether there are ten pairs that
are devoted to functions connected with the head, either as nerves of the
special senses or in a motor or sensory capacity (Figs. 26 and 27). There
are two pairs distributed to other regions. These are the tenth and
eleventh pairs. The tenth pair or pneumogastric is distributed to the vital
organs lodged within the body cavities.
There are forty-two or forty-three pairs of spinal nerves given off from
the spinal cord. The spinal nerves have two roots, superior and inferior.
The superior is the sensory root and the inferior is the motor root, both
uniting to form a mixed nerve trunk. The sensory root possesses a ganglion
from which it originates.
Generally speaking, the cerebrospinal system deals with the special senses,
movement of skeletal or voluntary muscles and cutaneous and muscular
sensations. In addition to the above there is a distinct system termed the
sympathetic. The _sympathetic system_ consists of a long cord, studded with
ganglia, extending from the base of the neck to the sacrum. The ganglia are
connected with the inferior roots of the spinal nerves. This cord is
connected with groups of ganglia and nerve fibres in the abdominal region,
and this in turn is connected with terminal ganglia in distant tissues.
This system of nerves is distributed to the vital organs of the body.
[Illustration: FIG. 26.--Unilateral facial paralysis caused by injury to
seventh cranial nerve; note position of lip.]
[Illustration: FIG. 27.--Bilateral facial paralysis. This colt was affected
with facial paralysis when born.]
CONGESTION AND ANAEMIA OF THE BRAIN.--In congestion of the brain, the
blood-vessels distributed to the nerve tissue become engorged with blood.
It may be either active or passive.
_The cause of anaemia_ of the brain is an insufficient blood supply. This
may be due to an abundant haemorrhage and cardiac weakness caused by shock
or organic heart disease.
_The causes of congestion_ of the brain are faulty methods of care and
feeding. It sometimes occurs when horses are shipped in poorly ventilated
cars, or kept in close stables. Climatic changes, or changing the stable
and feed, may cause it. Extremely fat animals and animals that are rapidly
putting on fat are predisposed to this disorder. Improper methods of
feeding, lack of exercise, constipation and excitement are the most common
causes. Passive congestion may result from pressure on the jugular vein by
obstructing the flow of blood from the brain, and raising blood pressure in
the blood-vessels of the brain. It is sometimes caused by organic heart
trouble.
_The symptoms_ come on very suddenly in congestion of the brain. The
disease may manifest itself as soon as the animal is moved out of the stall
or bed, or it may come on while it is feeding. In slight cases, the animal
appears excited and restless, the eyes are bright, the pupils are dilated,
and the pulse beats and respirations quickened. If the animal is moving
about, it may stop suddenly and show marked symptoms of a nervous disorder,
such as turning around, running straight ahead and falling down. The period
of excitement is usually brief and may be followed by marked depression.
The mucous membranes of the head are a deep, red color.
_The symptoms_ in anaemic conditions of the brain are loss of
consciousness, stumbling, falling to the ground and sometimes convulsions.
The pig and dog may vomit. Favorable cases return to the normal within a
few hours. Acute inflammatory diseases of the brain and its coverings are
associated with cerebral hyperaemia or congestion.
_The treatment_ of mild cases is to give the animal quiet, well-ventilated
quarters, where it can not injure itself. The animal should be first
subjected to a severe diet and later given easily-digested feed. If it
appears greatly excited, bleeding should be practised. Cold applications to
the head should be used in all cases in the small animals. For internal
treatment, purgatives are indicated. In cases of anaemia, stimulants,
vigorous massage, artificial respiration and injection of physiological
salt solution are indicated.
SUNSTROKE AND HEATSTROKE.--Most writers make no distinction between
heatstroke and sunstroke. The latter is caused by the direct rays of the
sun falling on the animal, and the former from a high temperature and poor
circulation of air in the surroundings. Under such conditions, the physical
condition of the animal and exertion play an important part in the
production of the nervous disturbance.
_The first symptoms_ usually noted are rapid, labored breathing, depression
and an anxious expression on the face. The horse usually stops sweating.
The body temperature is extremely high, the pulse beats weak, the animal
trembles, falls to the ground and dies in a convulsion. Unless measures
directed toward relief of the animal are taken early in the attack, death
commonly occurs. Overheating is rather common in horses that are worked
hard during the extremely warm weather. Horses that have been once
overheated are afterwards unable to stand severe work during the hot months
of the year. Horses in this condition become unthrifty, do not sweat freely
and pant if the work is hard and the weather is warm.
_The preventive measures_ consist in not exposing animals that are fat, or
out of condition to severe exercise if the day is close and hot, especially
if they are not accustomed to it. When handling or working animals during
hot weather all possible precautions to prevent overheating should be
practised.
_The treatment_ consists in placing the animal in a cool, shady place and
fomenting the body with cold water. The cold packs or cold fomentations
should be applied to the head and forepart of the body only. Small doses of
stimulants may be given.
MENINGO-CEREBRITIS.--The discussion of inflammation of the brain and its
coverings can be combined conveniently, as the causes, symptoms and
treatment vary but little. This disorder is met with in all species of
domestic animals, but it is most common in horses and mules. Some writers
state that meningo-cerebritis is more common during the warm season than it
is in the winter. However, this does not hold true in all sections. In the
middle west, this disease is more common in late fall and winter.
_It is commonly caused_ by taking into the body with the feed and water
certain organisms and toxins that are capable of producing an inflammation
of the brain. The infectious organism or toxins are taken up by the
absorbing vessels of the intestines.
The secondary form of the disease usually occurs in connection with other
diseases such as influenza, tuberculosis and acute pharyngitis, or as a
result of wound infection. Unhygienic conditions, as unsanitary and poorly
ventilated stables and filthy drinking places, play a very important part
in the production of the simple or acute form of meningitis.
Sudden changes in the feed and the feeding of rotten, mouldy feeds may
cause it. In the fall and winter it may follow the feeding of too heavy a
ration of shredded fodder or any other dry feed. Other exciting causes are
overexertion, changes in climate, excitement, injuries to the head and the
feeding of too heavy and concentrated a ration.
_The symptoms_ vary in the different individuals, but in general they are
the same. At first the animal is dull, or extremely nervous and sensitive
to sounds. The pupils of the eye are unevenly contracted at first, later
dilated. The eyes may appear staring, or they are rolled about, so that the
white portion is prominent. The unusual excitement is manifested in
different ways by the different species. During the dull period the animal
is indifferent to its surroundings. When it is excited, the pulse beats and
respirations are accelerated. The body temperature is often elevated early
in the disease. There is a partial or complete loss of appetite. Paralysis
may be the most prominent symptom. The animal lies in a natural position,
or stretched out and lifting the head occasionally and moving the limbs,
but it is unable to rise. Loss of sensibility may gradually progress until
the animal becomes semiconscious, or comatose.
In case the inflammation is acute and involves the greater portion of the
brain and its coverings, death occurs within a few days. Occasionally the
animal survives several weeks. There are few permanent or complete
recoveries.
_The principal lines of treatment_ are preventive measures and careful
nursing. This is one of the diseases that can be largely prevented by
observing all possible sanitary precautions in caring for animals. It is
admitted by writers that the greater majority of cases of inflammation of
the brain and its coverings are caused by infection. Proper stable
construction, ventilation and disposal of the manure, an occasional
disinfection of the stable, cleaning and disinfecting the drinking places
and water tanks, and the necessary attention to the ration greatly reduce
the loss from this disease.
The animal should be gotten into a dark, quiet, roomy stall that is well
bedded. A swing may be placed under a large animal if it is able to support
any of its weight, and there is no evidence of nervous excitement. We
should do nothing to disturb it. If possible, the position of the animal
that is unable to get up should be changed, and the bed kept clean and dry.
Cold in the form of wet or ice packs should be applied to the head during
the acute stage. Symptoms of excitement must be overcome by large doses of
sedatives. Iodide of potassium and strychnine may help in overcoming the
paralysis. The bowels should be emptied by giving an occasional physic. A
very light, easily digested diet should be fed.
PARTIAL OR COMPLETE PARALYSIS OF THE POSTERIOR PORTION OF THE BODY.--This
disorder is especially common in the small animals. The hog is most
frequently affected.
_The following causes_ may be mentioned: Inflammation of the spinal cord
commonly occurs in influenza, strangles and mixed infections; constipation
brought on by improper feeding and insufficient exercise is a predisposing
cause; injuries such as strains and blows in the region of the back may
also cause it; compression of the spinal cord by the vertebrae is no doubt
a very common cause; dislocation, enlargement of the disks between the
vertebrae, bony enlargements resulting from strains and injuries, rickets,
tuberculosis and actinomycosis and tumors commonly cause compression of the
cord. It is rarely caused by parasites. Young, fat animals are especially
prone to injuries in the region of the back. Such animals may suffer from
malnutrition of the bones, and complete fractures of the thigh bones may
occur. Extreme heat from the sun's rays and close, hot quarters are
probable causes.
_The symptom_ that is most prominent is the partial or complete loss of
control over the movements of the hind parts. The appetite may be little
interfered with. The animal may sit on the haunches, with the limbs
projecting forward, or swing the hind quarters from side to side in walking
or trotting. Irregularity in the animal's movements is especially
noticeable when turning or backing. In case the animal suffers pain, the
spine is held rigid or arched, and when forced to move, marked evidence of
pain occurs. There may be a decrease or increase in the sensibility of the
part. The increase in sensibility is noticed on striking the muscles with
the hand or rubbing the hair the wrong way. Spasmodic twitching or
contractions in the muscles sometimes occur. There is frequent elevation of
temperature. The animal is unable to pass urine or faeces, or there may be
an involuntary passage of the body excretions.
The outcome of this disease is unfavorable. Acute inflammation of the
covering of the cord may subside within a few days. Cases that do not
recover within a few weeks should be destroyed. Paralysis of the hind parts
should not be confused with rheumatism, azoturia and other disorders that
may interfere with the movements of the posterior portion of the body.
_The treatment_ is largely along preventive lines. A predisposition toward
rickets, and injuries, may be prevented by feeding a proper ration, and
permitting the animal to take exercise. The quarters and the attendant are
frequently responsible for injuries. If this is the case, the rough
handling of the animals should be immediately corrected, and any condition
of the quarters that favors the crowding or piling up of animals should be
changed. Large animals may be placed in swings if they are able to support
a part of their weight on the hind limbs. This is especially indicated at
the very beginning of the disorder. Small animals should be given a good
bed. A very light, easily digested ration should be fed. An occasional
physic should be administered. Strychnine and iodide of potassium may be
given. Cold applications to the back are indicated.
QUESTIONS
1. What organs comprise the central portion of the nervous system?
Peripheral portion?
2. Give a general description of the brain.
3. Give a general description of the spinal cord.
4. What is the sympathetic system?
5. Describe the causes and symptoms of congestion of the brain.
6. What is heatstroke? Give the treatment.
7. Give the preventive and curative treatment of inflammation of the brain.
8. State the causes, and give the proper treatment of paralysis of the
posterior portion of the body.