Nerve (biology)

“ 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. ”

“ 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. ”

“ 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. ”

“ In the most complex case, that of man, there are a number of nerve-endings, or small lumps of protoplasm, embedded in the tissues all over the body, or highly specialised and grouped together in separate organs such as the eye and ear, from which a nerve-fibre leads direct to the brain, or to the spinal cord and so up to the brain. These nerve-endings receive the different vibrations by which outward energy presents itself, which propagate a current or succession of vibrations of nerve-energy along the nerve-fibre. ”

“ Now, the nerve-fiber which conveys the energy of the sensation is a round thread of protoplasm which in all probability connects the nerve-ending with a sensory corpuscle in the spinal cord. These nerve fibers running in nerves are white, whereas, as you know, protoplasm is gray. They are white because each is insulated from its fellow by a white sheath of fatty substance, just as we protect telegraph-wires with coatings. It is not stretching analogy too far to say that nerve force may probably escape unless properly insulated. ”

“ 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. ”

“ 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-tissue must be understood as having everywhere the same general Property. In one animal and in another, in one part and in another, Neurility is the same in kind, but not everywhere manifesting the same degree, nor applied to the same Function. The composition of nerve-tissue varies, but not more than the composition of all other organized substances; the structure is variable, but only within a small range ”

“ If we dissect the body of any animal or bird, we can find nerves passing to various parts. For example, a large nerve goes down each leg; this nerve subdivides here and there. Since we know that the nerve consists of a great many axons bundled together, we will realize that this subdivision is not a real branching, but simply a passing of some of the axons away from the main trunk along the smaller stem. Some of these smaller stems can be traced to endings in the skin; these contain the axons connecting with sense organs. Others lead directly into muscles. ”

“ One of the most interesting discoveries of physiology was the discovery, made simultaneously in France and Germany fifty years ago, that nerve currents do not only start muscles into action, but may check action already going on or keep it from occurring as it otherwise might. Nerves of arrest were thus distinguished alongside of motor nerves. The pneumogastric nerve, for example, if stimulated, arrests the movements of the heart: the splanchnic nerve arrests those of the intestines, if already begun. ”

“ It cannot be denied that in rare instances these various agents are productive of pain referred to a particular nerve, when we cannot find anything in the nerve itself or in the tissues supplied by it to account for the morbid manifestation. We are, therefore, constrained to believe, at least for the present, that morbid manifestations, sensations of pain, may originate in the cell itself and thence be referred outward. ”

“ 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 ”

“ Nero fled from Rome, was declared an enemy of his country, and to save himself from execution committed suicide. See W. Wolfe Capes' Early Roman Empire and Merivale's History of the Romans under the Empire.
Nerves, the fibers of white nervous matter connecting the different parts of the body with the central nervous system. Two kinds of nervous tissue are recognized,— the white and gray. The white is composed of fibers, the gray is largely made of nerve cells located in centers. The nerves are merely conductors of the nervous impulses that arise within the nerve-cells. ”

“ At the surface of the body and limbs, the external termini of the nerves are exposed to disturbance by contact with an external object. Along the highly sensitive and minute conductor, the nerve which has by contact with an external object at its outer extremity received a slight shock, there passes through the fluid or semi-fluid substance of the nerve a wave of disturbance, or a succession of such waves. This disturbance reaches the brain, the great nerve-center, where it becomes a feeling. ”

“ 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. ”

“ Nerve-tissue has the peculiar faculty of transmitting impressions made upon it by stimuli. When a nerve is acted on by a stimulus, the impression wave is transmitted along the in-going nerve to the ganglion; here, the stimulus is transferred to the out-going nerve, which, going to the muscle, causes it to contract. ”

“ The incoming nerve-fibres serve to conduct stimuli or impressions to the cells in the nerve-centre; and, when the cells thus receive a stimulus or impression, they liberate a discharge of nervous energy, which then courses down the outgoing nerve-fibres to be distributed either to other nerve-centres or else to muscles. It is in this way that nerve-centres are able to act in harmony with one another, and so to coördinate the action of the muscles over which they preside. This fundamental principle of neurosis is what physiologists call the principle of reflex action ”

“ The deeply stained oblong nuclei indicate the nerve corpuscles within the neurilemma.
264. The Nervous System Compared to a Telegraphic System. In men and other highly organized animals, nerves are found in nearly every tissue and organ of the body. They penetrate the most minute muscular fibers; they are closely connected with the cells of the glands, and are found in the coats of even the smallest blood-vessels. They are among the chief factors of the structure of the sense organs, and ramify through the skin. ”

“ 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." ”

“ The great peculiarity of their innervation consists in the fact that their nerves all belong to the branchial system of nerves; no fibres arise in connection with the trigeminal, but all of them in connection with the facial, glossopharyngeal and vagus nerves. In other words, although organs in the skin, their nerve-supply belongs to the lateral nervous system which supplies splanchnic and not somatic segments, a system which, according to the theory advanced in this book, originated in the nerves supplying appendages. ”

“ Cut off the leg of a frog, and resect its sciatic nerve, the muscles will for some time retain their property (Contractility) , and will contract on being stimulated. The nerve also retains its property (Neurility) , and on being stimulated, it will excite the muscles to contraction. We know that muscles will contract without the intervention of nerves, and that glands will secrete without the intervention of nerves. It is also probable that the sensorium may be stimulated without the direct intervention of nerves. ”

“ But in all cases in which there is anything like real "fits," it will be found of great importance to study the over-and-under-actions of the nerve system as by far the most essential elements in the disease. ”

“ Anatomical research has traced the ramification of the nerve through all the fibre entirely diffused even till lost in pulp, and no one I believe has reason to doubt the complete dependence of sensibility on the presence of the nerves, yet there is no instrument, however sharp, that can touch a single point in a muscle without producing a sensation more or less acute; which circumstance shews the entire distribution of the nerves. ”

“ If the nerve in a limb of a living animal be laid bare, and irritated by pinching, galvanizing, or the like, two results follow, namely: the animal experiences a sensation, that of pain, in the part to which the nerve is distributed, and the limb is thrown into convulsive action. When a nerve in a human body is cut by accident, or destroyed by disease, the part in which it ramifies loses both sensation and power of motion ”

“ If the nerve is not cut, but laid bare by a wound, the surrounding skin being divided so that the nerve appears naked, and is wounded longitudingly and not transversely, we must use none of the afore-mentioned from euphorbium, nor any thus acrid, for the nerve being bare will not bear their power which is strong, but one may use lime that has been washed often in the warm season mixed with much honey. ”

“ 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. ”

“ In experiments, the animal sensibility of the nerve seems to be gradually exhausted, and finally ceases. I convinced myself of this upon the eighth pair of nerves, in making my experiments upon the injection of black blood into the brain. At the moment the nerve is raised and drawn to detach it from the carotid with which it is connected, the animal cries out and is much agitated; but after the same thing is repeated two or three times, he208 no longer gives any signs of pain. If we cease to excite the nerve for an hour or two, the sensibility returns with great energy, when it is drawn again. ”

“ Experience shows that nerve-force is generated and set free whenever the cerebro-spinal system is excited. The direction which this nerve-force follows is necessarily determined by the lines of connection between the nerve-cells, with each other and with various parts of the body. ”

“ Certain organs in which the cerebral nerves evidently enter, as the liver, the lungs, &c. can be irritated in animals, without seeming to give them much pain. 3d. The muscles of animal life, in the structure of which so many nerves enter, in which also the branches of these perform so great a part as it relates to animal contractility, do not occasion much pain when their texture is cut without entangling the nervous filaments that penetrate them. 4th. The ligaments, that no nerve enters, are the seat of acute pain when they are distended, as my experiments have proved. ”