Nerve tissue

“ 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. ”

“ Also, since it is noted that each nerve cell presides over the nutrition of its own processes and possesses its own power of repair, it follows that unless an173 injury be of fatal nature or of permanent duration, even injuries to nerves tend toward automatic cure. We must seek a permanently operating interference with nerve tissue. ”

“ So much is certain, that in that region, where arteries and veins are not to be seen, there are also no separate nerve twigs, and that here the union or coalescence of nerve and tissue which the nerves are to influence must have taken place. If one considers the fine meshes of the capillary network enveloping the ducts, and keeps in mind the abundance of nuclei belonging to the capillary, the membrana propria and the duct cells proper, he can imagine how difficult it must be to follow the course of the nerves through and among all these structures. ”

“ The course of the nerve is preserved by its intact connective-tissue framework, and ultimate recovery by a regeneration of the nerve fibres is more likely to be complete, and will be just as rapid, if nature be relied on and the nerve be left untouched by the hand of the surgeon.
It is, I think, undeniable that nerve trunks may escape severe or irrecoverable injury by lateral displacement. The mere fact that the trunk itself may be perforated by a slit in its long axis would suggest the possibility of displacement of the whole structure, and this no doubt occurred with some frequency. ”

“ Once the nerve cell is developed and safely shifted into the interior of the body, it is clothed with a protecting feltwork of connective tissue, and the nerve fibres are also surrounded by connective-tissue cells which secrete around them the fatty substance which makes nerves look white.
Such is the nerve cell or intermediary between the world and the muscles; but thence to harmonious movement in a body with complex organs capable of varied actions is a long step. ”

“ The fibres which emanate from them are very delicate, and, becoming mixed with others, do not admit of being further traced. Where the nervous tissue meets the enveloping epithelium it is connected with the latter from within, but differs widely from it; for the nerve-cells contain a longitudinally striated cylindrical or thread-like nucleus which carries on its peripheral end a delicate hair, while its central end is prolonged into a fine nerve-fibre. There are, besides these, two other kinds of cells which form a transition between the ganglion and the epithelium cells. ”

“ 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. ”

“ Each nerve cell is trophic to its processes and to the tissue cells to which these processes are distributed. The growth, nutrition and repair of each cell of the body is dependent upon the integrity of the axon which supplies it. The effect of nerve impingement upon the single cell is a weakening of cell structure and a disturbance, slight or great, of the special function possessed by that cell. ”

“ 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. ”

“ 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 tissue composing the nerves is entirely of the white variety, or, in other words, the nerve-fibres; the same as we have observed forming a part of the brain. But the nerves, instead of being soft and pulpy, as in the case of the brain, are dense in structure, being hardened and strengthened by means of a fibrous tissue which surrounds each of these delicate fibres, and binds them together in glistening, silvery bundles. ”

“ In order to control the functions of the various organs and tissues and to regulate the rate at which they reproduce themselves, the nerves extend their terminal branches, not only into every tissue, but into every microscopical unit of such tissue, and the part of the cell which represents the nerve terminal is the inner structure called the nucleus. ”

“ The nerve fibers represent a conducting apparatus and serve to place the central nervous organs in connection with peripheral end organs. The nerve cells, however, besides transmitting impulses, act as physiological centers for automatic, or reflex, movements, and also for the sensory, perceptive, trophic, and secretory functions. A nerve consists of a bundle of tubular fibers, held together by a [Pg 211] dense areolar tissue, and inclosed in a membranous sheath—the neurilemma. Nerve fibers possess no elasticity, but are very strong. Divided nerves do not retract. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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 enormous preponderance of cases of pain of the fifth nerve, compared with other nerves, is to be accounted for by the liability of the delicately adjusted mechanism of the organs supplied to get out of order. ”

“ 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. ”

“ 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 anatomical effects of nerve-stretching are manifold. Nerve-fibres are usually destroyed in greater or smaller number, and the conducting power of the nerve correspondingly impaired. Small blood-vessels are broken and the circulation and nutrition of the nerve-trunks altered, and it is probable that adhesions in and around the nerve-sheaths, where such exist, are severed. ”

“ 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? ”

“ The remaining nerves, all of which have their origin in the medulla oblongata, possess certain features in common, and as they are related to the gill-clefts in such a way that each forks over a cleft, they may be conveniently distinguished as "branchial" or "branchiomeric nerves." A typical branchial nerve consists of (1) a principal ganglion near the origin of the nerve from the brain; (2) a main trunk which gives off (3) a somatic sensory branch or dorsal nerve to the skin; (4) a palatine nerve (visceral sensory) to the oral or pharyngeal mucous membrane ”

“ Take a living frog, and after amputating the hind legs, (for they are the best, on account of the number of joints) let the largest nerve, called the crural nerve, be laid bare, and surrounded with a slip of tin-foil, or a piece of sheet lead—then lay a piece of zinc, or other metal different from that on the nerve, in contact with the neighbouring muscles; form a communication by another piece of zinc, or other good conductor, between the metal in contact with the muscle and the armed part of the nerve, and violent contractions will be produced in the limb. ”

“ If the continuity of the fibres of a mixed nerve be destroyed at some point in its course by cutting, bruising, pressure, traction, the application of cold, the invasion of neighboring disease, etc., there will be an immediate loss of the functions dependent on the nerve in the parts to which it is distributed. ”

“ In all the other nerves it is much more difficult to examine well this medullary substance, because the nervous coat that contains it, is as much or even more developed in proportion to what it will be afterwards. Hence it is that the nerves are very hard and resisting in the fœtus; and that they can support weights proportionably very great. Maceration in water, at a moderate temperature, increases this resistance as in the adult, and renders the nerve harder without increasing its size. ”

“ 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. ”

“ The nervous system, notwithstanding the fact that the three last thoracic segments are free, is chiefly concentrated into a mass surrounding the oesophagus. Nerves are given off in front to the eyes, the labrum, and the chelicerae, while double nerves radiate to the pedipalps and to the legs. From behind the nerve-mass three nerves emerge, and pass through the diaphragm to enter the abdomen. The median nerve swells into an “abdominal ganglion” just behind the diaphragm, and is then distributed to the diverticula of the alimentary canal. The lateral nerves innervate the generative organs. ”

“ The seventh nerve (facial) is almost entirely motor; it passes through the periotic anterior to VIII., and emerges by the stylo-mastoid foramen (s.m.f.) behind the bulla, to run outside the great jaw muscle across the cheek immediately under the skin (Figure 1) .
Section 129. The ninth (glossopharyngeal) nerve is chiefly sensory; it is the special nerve of taste, and is distributed to the tongue. The tenth nerve (vagus) arises by a number of roots, and passes out of the skull, together with IX and XI, by the foramen lacerum -posterium- [posterius] (f.l.p.) ”

“ 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. ”