Neurology

“ We should remember that the nervous system is one continuous structure, and it is only the necessities of nomenclature and the ingenuity of anatomists that have divided it into so many parts. It is as continuous as is an oak tree with its various branches. The spinal cord and the nerves are composed in varying proportions of the same materials as is that part of the system which we call the brain: injury and disease with them give rise to symptoms analogous to similar injury or disease to the brain. ”

“ By the separation of a main branch of one of the nerves of sensation, although all the operations of life will still proceed, the organ to which that nerve goes is dead to its particular sense. In like manner, if one of the nerves of volition is divided, the member will not obey the inclination of the brain. It is evident, therefore, although many of the great phenomena of vital force are dependent on the nervous system, and the paralysis of a member ensues upon the separation or the disease of a nerve, that the nerves are but the channels through which certain influences are carried. ”

“ In order that the lay reader may clearly apprehend the various bearings of the facts, and the intimate relation of the diverse symptoms to each other in tobacco-sickness, it is, perhaps, necessary to map out the pneumogastric nerve and indicate its function, which is not fairly deducible from its name. The origin of nearly every pair of cranial nerves has been traced into the vital bulb, the medulla oblongata, or continuation and expansion of the spinal cord as it passes into the cranium, to blossom into the complex structure of the brain. ”

“ The brain is intimately associated with the entire physical person by twelve pairs of cranial or cerebral nerves, and by the spinal cord, which descends from the base of the brain through a great foramen or opening midway between the ears, and while passing down the spinal column gives off thirty pairs of nerves.
The cranial nerves are all for the head, except the pneumogastric or lung-stomach nerve, which belongs to the organs of respiration, voice, and digestion; and the spinal nerves are all for the body, except a few which ramify in the neck and in the scalp. ”

“ In other words, there is every reason to believe that numerous "centres," in this restricted sense, exist in the brain that have as yet eluded the investigator. Indeed, the current conception regards the entire cerebral cortex as chiefly composed of centres of ultimate co-ordination of impressions, which in their cruder form are received by more primitive nervous tissues—the basal ganglia, the cerebellum and medulla, and the spinal cord.
This, of course, is equivalent to postulating the cerebral cortex as the exclusive seat of higher intellection. ”

“ Disease of the nervous system does not differ from disease elsewhere. The system is complex in structure and in function. It consists in nerves which are composed of very fine fibrils distributed in all parts of the body and serve the purpose of conduction, and a central body composed of the brain and spinal cord which is largely cellular in character; it receives impressions by means of the nerves and sends out impulses which produce or affect action in all parts. ”

“ The cerebrum, or fore brain, is divided into two hemispheres, each of which is further divided into numerous lobes consisting of grey and white nervous substance and millions of nerve cells and fine blood vessels. The hemispheric ganglia are the instruments through which the intellectual powers manifest themselves. If these instruments have become imperfect in structure through retarded development by wrong environment and education, or have been damaged in any manner by severe shock, violence or disease, the manifestations of intelligence are affected in a corresponding degree. ”

“ Intellect, Emotion, and Volition. Physiologists assign to the cerebrum its functions, and neurological, as well as phrenological writers, have located them as represented in Fig. 68. True, there is no structural division between the parts of the cerebrum to indicate this diversity of function, nor is there any perceptible limit between the sensory and motor filaments of the game nerve. As no one has any reason for denying that separate portions of the brain may manifest distinct functions of the mind, we shall assume it as a conceded proposition. ”

“ In the skull, besides the larger openings we have spoken of, you will find several small holes leading from the outside of the skull into the inside of the brain-case. Some of these holes are filled up during life by blood-vessels, but in others run those delicate white threads or cords which you have already learnt to call nerves. Nerves are in fact branches of nervous material running out from the brain or spinal cord. Those from the brain pass through holes in the skull, and at first sight seem to spread out very irregularly. Those which branch off from the spinal cord are far more regular. ”

“ The anatomy and physiology of the last century, however, prepared the way for the successful elucidation of the subject, and the first great step forward was made by Sir Charles Bell about the year 1825, in establishing the double action of the nervous system, or that impressions from the external world pour in upon the brain through one set of nerve-lines, while all the mandates of volition controlling human activity are transmitted outward along another system of nerve-lines. ”

“ In the medulla the nerves that arise in the cerebrum cross over from one side of the body to the other on the crossed pyramidal tracts. The importance of this crossing of the nerve fibers is seen in apoplexy, when a blood-vessel is ruptured in the brain and hemorrhage causes pressure, generally on the motor tract. Paralysis of the nerves and of the muscles to which they go results. The paralysis is generally of one side of the body, the opposite side from that on which the injury occurred. ”

“ From it in turn come a great many connecting nerve cells whose axons pass along the spinal cord and form nerve junctions with the motor nerve cells; and so nervous disturbances coming from the cerebellum can arouse the muscles to activity. We all know that walking or any other locomotor act, after it has once been learned, is carried on successfully without our performing any intellectual work in connection with it. What we do have to do is to start the act, and this is done through a discharge from the cerebrum ”

“ The higher functions of the nervous system, which make up our conscious mental life, are merely more complex modifications of this fundamental property of nerve substance. Closely related to this doctrine is the view that the nervous organism acts as a whole, that particular mental operations cannot be referred to definitely circumscribed regions of the brain, and that the hypothesis of nervous activity passing in the centre by an isolated pathway from one nerve-cell to another is altogether illusory. ”

“ Central Nervous System.—The neural tube shows in very early stages an anterior dilated portion which forms the rudiment of the brain in contradistinction to the hinder, narrower part which forms the spinal cord. This enlargement of the brain is correlated with the increasing predominance of the nerve centres at the anterior end of the body which tend to assume more and more complete control over those lying behind. ”

“ The air from the lungs is forced past them, setting them in vibration, thus producing sound.
The nervous system consists first of all of the brain. This is composed of nervous matter and constitutes the mass contained in the skull. It is divided into three parts: the cerebrum, the cerebellum, and the medulla oblongata. These three parts seem to preside over different functions. Thus, the cerebrum is the seat of the faculties of the mind, while the cerebellum presides over the muscular actions. ”

“ With disease or willful destruction of the cerebral tissue the personal initiative is affected-- the animal becomes more distinctly a mechanism; the cerebellum is probably concerned in the coordination of muscular movements; and the medulla is a centre for the higher and more complicated respiratory reflexes, yawning, coughing, and so on. The great majority of reflex actions centre, however, in the spinal cord, and do not affect the brain. ”

“ Neither medicine nor physiology opposes the use of the clinical method in cerebral localization. But only circumscribed lesions that have little or no tendency to become general, or to act at a distance by compressing the brain, or otherwise, can come to the aid of our theory. When there is a lesion of the cortical region of the brain which fulfills these conditions, the resulting symptoms may be of two orders—either stimulative or paralytic of the true function. ”

“ The lower centers are directly connected by nerves with the sense organs, glands and muscles, while the higher centers have direct connections with the lower and only through them with the sense organs, glands and muscles. In other words, the sensory nerves run into the cord or brain stem, and the motor nerves run out of these same, while interconnecting nerve strands extend between the lower centers in the cord and brain stem and the higher centers in the cerebrum and cerebellum. ”

“ That the nervous tissue of the cerebrum should be thus the instrument of the mind need not surprise us when we think how the muscles and joints of the tumbler, the vocal organs of the singer, the finger-ends of the watchmaker; the palate of the tea-taster, grow to the uses they are steadily put to; and, much more, both in the case of the brain and all other organs, grow to the uses they are earliest put to. ”

“ The Fifth Nerve. The thinning of the roof of the brain, in the manner already described, produces a great change in the apparent position of the roots of all the nerves. The central ends of the rudiments of the two sides are, as has been mentioned, at first in contact dorsally but, when by the growth of the roof of the brain its two lateral halves become pushed apart, the nerves also shift their position and become widely separated. ”

“ The nerve supply is abundant and peculiar. The integument receives sensory branches from the fifth cranial nerve, the blood-vessels are under the control of the sympathetic system, and the muscles which have to do with expression receive motor impulses from the brain via the seventh cranial or facial nerve, first accurately described by Sir Charles Bell. ”

“ But these volitional, emotional and visual centers are widely spread over the cortical area. About their special connections with one another, and especially with the center of the accessory nerve, under normal conditions, we are much in the dark. And how they could go to work to solve, in any length of time and even partially, the problem of readjusting their functional relations to the new and abnormal conditions, offers a problem as yet quite unanswerable by cerebral physiology. ”

“ Its cerebral area includes the posterior and inferior portions of the cerebrum, the entire cerebellum, and that part of the medulla which connects with the spinal cord, all of which sustain intimate relations to vital conditions. Accordingly, such a development indicates good digestion, active nutrition, vigorous secretion, large heart and lungs, powerful muscles, and surplus vitality. The violent faculties, such as Combativeness, Destructiveness, and Hatred, are natural adjuncts, and their excess tends to sensuality and crime. ”

“ Incoming nerve-currents are the only agents which normally affect the brain. The human nerve-centres are surrounded by many dense wrappings of which the effect is to protect them from the direct action of the forces of the outer world. The hair, the thick skin of the scalp, the skull, and two membranes at least, one of them a tough one, surround the brain ”

“ The medulla is part of the brain stem.
This was only one of the difficulties which had to be overcome. The eyes are set on the pre-fulcral lever of the head. For our safety we must be able to look in all directions—over this shoulder or that. We must also be able to turn our heads so that our ears may discover in which direction a sound is reaching us. In fashioning a fulcral joint for the head, then, two different objects had to be secured: free mobility for the head, and a safe transit for the medullary part of the brain stem. ”

“ Thus, for instance, when the nervous continuity of the spinal cord is interrupted, so that a stimulus applied to the lower extremities is unable to pass upwards to the brain, the feet will be actively drawn away from a source of irritation without the man being conscious of any pain; the lower nervous centres in the spinal cord respond to the stimulation, but they do so without feeling the stimulus. ”

“ From what has been said, it is clear, that the nerves do not arise deep in the cerebral substance, at least in an apparent manner, but take their origin from its external surface. Many physiologists however, have admitted an origin more remote than can be proved by examination. They have believed that the nerves of one side arise from the opposite, and that each pair cross each other not only in the brain, but also in the spinal marrow. ”

“ Caudad to the cerebrum are seen the end of the paraphysis, G.p., the optic lobes, MH, and the cerebellum, HH. From the cerebral peduncles (ventrad to the optic lobes) arises the oculomotor nerve, III, and dorsocaudad to this, between the optic lobe and the cerebellum, arises the trochlear nerve, IV. From the middle zone (in a dorsoventral direction) of the medulla, ventrad to the cerebellum, arises the very large trigeminal nerve, V; while from its usual place, on the ventral surface of the medulla, the abducens nerve, VI, takes its origin by several roots. ”

“ All the spinal nerves, and two from the brain, are concerned in both sensation and motion. Of the remainder of the cranial nerves, some are exclusively motor, others exclusively sensory; and still others convey, not ordinary sensations, but special impressions, such as sight, hearing, and smell, which we have yet to consider. However much the functions of the nerves seem to vary, there is but little difference discoverable in the nerves themselves, when examined under the microscope. ”