Nerve center

“ Owing to the existence of a chain of neurons, that is, a succession of nervous elements, instead of one continuous nerve fiber from center to periphery, it is possible for one of the neurons of the chain to be so disturbed that the conducting apparatus is interrupted and impulses do not flow. Hence, if a strong impression is produced on the mind with regard to a particular part of the body the neurons leading to it may be so disturbed that trophic nerve impulses do not flow down, the blood supply of the part may be disturbed through the vaso-motor system and consequent changes may take place. ”

“ Ingoing and outgoing nerve currents with their various end reactions may be modified by the nerve centers. Nerve currents' may be intensified, decreased in energy, or even entirely inhibited by central ganglia or by their mutual interaction and interferences. ”

“ In other words, nerve centers which are abnormally positive will cause other abnormally negative nerve centers to exist and prevent these from reaching a normal 146positive state. As a result the body cannot eliminate its waste matter, and reconstruction is almost impossible. ”

“ 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. ”

“ That which can be done in the way of producing severe pain by these severe affections of the peripheral portions of nerves, or of tissues lying outside them, we might a priori expect would be effected by slighter but continuous changes in the nutrition of the more important portion of the nerve itself—its central gray nucleus. ”

“ I expect, in short, to convince most readers that the essential seat of every true neuralgia is the posterior root of the spinal nerve in which the pain is felt, and that the essential condition of the tissue of that nerve-root is atrophy, which is usually non-inflammatory in origin. ”

“ If perturbation of nerve-function—a disturbance quite different from mere exaltation of the normal development of nerve-force—be the essence of pain, how comes it that pains of the severest type may be produced by changes in structures which are usually described, for practical purposes, as lying outside the nervous system? We must, in the first place, remark that the externality of any bodily tissue to the nervous system is more apparent than real. ”

“ Why is there not suffering produced, by the irritation of an insensible part that is at the side of a nerve, or even connected with it, whilst the pain is very acute in an inflamed part, though it is at a distance from every nervous cord? Would the nerves then have also, a sphere of activity for motion? But why should the contiguity of the nerve never be sufficient to produce it in the muscles? ”

“ In the same point of view it becomes clear also that, as the inclosing of the lower system in the higher one is characteristic of animal organization, and the rudiments of the nerves always show this peripherous type, the higher animals, and man in particular,—in whom the spinal nerves encompass the common cavity of the trunk, somewhat similarly to the bending of the ribs,—possess a system of nerves appropriated to the vegetative structure, and perfectly analogous to the nervous system of the inferior animals, namely, the ganglionic system, or that of the great sympathetic nerve. ”

“ The NERVES that are spread over every part of the sensitive layer of the true skin, proceed from the spinal cord. As a proof of the great number of nervous filaments in the skin, no part of this tissue can be punctured with a fine needle without transfixing a nerve, and inducing pain. In some parts of the system, however, the nerves are more abundant than in others; where the sense of feeling is most acute, we find the greatest number of nerves, and those of the largest size. ”

“ Tickling the soles of the feet in one who is asleep will cause them to be drawn up; irritation in the throat causes us to cough, or in the nose to sneeze; the flashing of a bright light into the eye compels us to wink; all these are examples of the direct passage of nervous disturbances from sense organs to muscles. In every case the path is from the sense organ over the sensory nerve cell to some point in the central nervous system, then either by a direct nerve junction to a motor nerve cell or over one or more connecting nerve cells to a motor nerve cell and so to the appropriate muscles. ”

“ Neuralgia in a sensory nerve can produce paralysis of muscles supplied by motor fibres bound up with the painful branch, or with another branch of the same nerve, or in muscles supplied by a totally distinct nerve connected only through the centre. ”

“ We have now presented some evidence that nervous energy is discharged by the adequate stimulation of one or more of the various receptors that have been developed in the course of evolution. In response to an adequate stimulus, the nervous system is integrated for a specific purpose by the stimulated receptor, and but one stimulus at a time has possession of the final common path— the nerve mechanisms for action. The most numerous receptors are those for harmful contact; these are the nociceptors. ”

“ If any one conceives that the anterior roots send forth nerves having a Neurility as widely opposed to that of the nerves issuing from the posterior roots as Motion is to Sensation, let his evidence be produced. If he conceives that the anterior nerves will only act in one direction, and the posterior in another and contrary direction, so that the motor nerve cannot excite a centre, and the sensory cannot excite a muscle or a gland, let him produce his evidence. ”

“ Through his efforts, and with the invaluable aid of such other workers as Remak, Purkinje, Henle, Muller, and the rest, all the mystery as to the general characteristics of nerve tracts was cleared away. It came to be known that in its essentials a nerve tract is a tenuous fibre or thread of protoplasm stretching between two terminal points in the organism, one of such termini being usually a cell of the brain or spinal cord, the other a distribution-point at or near the periphery—for example, in a muscle or in the skin. ”

“ The posterior nerve-roots, both within and without the cord, are frequently affected by the same kind of degeneration, which sometimes extends to the surface even of the lateral columns, and occasionally along the edges of the anterior. ”

“ 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. ”

“ General sensibility, whether of the internal or external organs of the body, chiefly depends upon the sensory fibres of the spinal nerve. The face, however, is supplied by the sensory cranial nerves. The sympathetic system has a low grade of feeling in health; but disease in the parts served by it arouses an intense degree of pain. ”

“ This change, as I have seen in my practice of medicine, sometimes passes up the nerves toward the centers, and occasions a more or less constant irritation of the nerve-fibers, producing neuralgia, which is usually referred by the brain to that part of the lost limb to which the affected nerve belonged. This pain keeps the brain ever mindful of the missing part, and, imperfectly at least, preserves to the man a consciousness of possessing that which he has not. ”

“ The lower nerve-centres form a system comparatively independent of the higher ones; corresponding to this is the fact that many bodily processes go on unconsciously and only make us aware of them when the circumstances attending them are particularly favorable or unfavorable. The consciousness of the physical state corresponds to the excitation of the higher nerve-centres. ”

“ Under this division it only remains further to be said, that section of the nerve-ring in the disc, or the nerve-trunks of the rays, although, as we have seen, so completely destroying physiological continuity in the rows of ambulacral feet and muscular system of the animal, does not destroy physiological continuity in the external nerve-plexus; for however much the nerve-ring and nerve-trunks may be injured, stimulation of the dorsal surface of the animal throws all the ambulacral feet and all the muscular system of the rays into active movement. ”

“ Nerve Stimuli.—While the properties of irritability and conductivity supply a necessary cause for the production and transmission of nervous impulses, these alone are not sufficient to account for their origin. An additional cause is necessary—a force not found in the nerve protoplasm, but one which, by its action on the protoplasm, makes it produce the impulse. In this respect, the neuron does not differ essentially from the cell of a muscle. Just as the muscle cell requires a stimulus to make it contract, so does the neuron require a stimulus to start the impulse. ”

“ They seem, at times, to be duly supplied, but the forces may as quickly depart and leave the system languid and depressed, without power to coordinate the muscles. This more especially applies to a certain class of cases which assimilate organic trouble in the nervous structure. No change observable takes place in the circulation, yet it must stand to reason that the replenishing power of the nerve-matter is deficient. ”

“ Alterations of sensibility occurring in well-defined areas of the hand, trunk, or extremities, corresponding to the known distribution of nerves, almost always indicates disease of the nerve itself, much more rarely disease in the spinal cord at the origin of the nerve. ”

“ All the operations of the nervous system are performed by the influence of the nervous fluid, which is generated in the gray portions of the brain and ganglia. Whenever a nerve is cut off from its connection with these nervous centres, its power is gone, and the part to which it ministered becomes lifeless and incapable of motion. ”

“ The liability to confound the affection with a neuritis more centrally situated, but the pain of which is referred to the periphery of the nerve, is to be obviated by a tracing of the nerve along its course to the nerve centre so as to identify any centre of tenderness, and also by the implication of all the peripheral branches coming off ectal of that point. ”

“ The action of nerves, under the pressure of extraordinary influences, may include all manner of vagaries which really have nothing in common with the effects of ordinary functional stimulation; which are, in fact, nothing but perturbation. No one can suppose, for instance, that the explosive disturbances of nerve-force which give rise to the convulsions of tetanus are any mere exaggerated degree of the orderly and symmetrical action by which the healthy nerve responds to the stimulus of volition ordering a given set of muscles to contract ”

“ The first attacks in all forms of neuralgia are often comparatively light, and the severity of the pain gradually increases as the attacks multiply. We have frequently had patients unacquainted with anatomy, map out the distribution of a nerve very perfectly, simply describing the portion of the body in which the pain was experienced. ”

“ With the field thus narrowed for us, it is surely legitimate, in the necessary scarcity of anatomical records referring directly to the state of the nerve-roots in ordinary neuralgia, to place great weight on the facts of a disease like locomotor ataxy, in which the main anatomical change is a progressive atrophy of the posterior columns which usually falls with peculiar severity on the posterior nerve-roots, or on the parts of the gray matter immediately adjoining these, and in which neuralgia may be said, for practical purposes, to be a constant and most characteristic phenomenon. ”

“ The nerves also undergo division until they terminate as fine thread-like structures in all parts of the body. The distribution of nerve terminations, however, is not uniform, as might be supposed, but the skin and important organs like the heart, stomach, and muscles are the more abundantly supplied. On many of the nerves are small rounded masses, called ganglia, and from many of these small nerves also emerge. At certain places the nerves and ganglia are so numerous as to form a kind of network, known as a plexus. ”

“ The nerve-ring is well supplied with epithelial and ganglionic nerve-cells; their function is wholly reflex and involuntary; they preside over the pulsing or swimming movements of the nectocalyx. This pulsing is excited by stimulation, and is analogous, so far as movement is concerned, to the peristaltic action of the intestines. Situated on the margin of the bell are a number of very minute, round bodies, the so-called "eyes." ”