Sensory system

“ In my own case, by that union of consciousness with physical energy which accompanies the manifestation of life, I am immediately related with that portion of the energetic system which is the real substratum of my organism, and am made conscious of the series of transmutations occurring at that particular point in it which is represented by my sensory system. In the case of others, from certain of the transmutations occurring in my Presentment, I am led to infer the existence of other similar microcosmic systems in the energetic macrocosm of the physical universe. ”

“ Thus the two sciences of astronomy and physiology discovered and developed the methods of investigating mental times; the further development was the task of psychology.
Another source of the new psychology is to be found in the physiological study of the sense organs. The most obvious method for determining the functions of the nerves and end organs of the skin—the nose, the ear, or the eye—is to ask the living subject what he feels when various stimuli are applied. In this way there has arisen a large body, of knowledge concerning the sensory functions of the nervous system. ”

“ Having now considered a nervous system reduced to its lowest possible terms, in which all the paths are connate, and the possibilities of inhibition not extrinsic, but due solely to the agreeableness or disagreeableness of the feeling aroused, let us turn to the conditions under which new paths may be formed. Potentialities of new paths are furnished by the fibres which connect the sensory cells amongst themselves ”

“ The arrangement of the nervous system is very much like that of a city telephone system. The sensory nerve cells all lead into a part of the nervous system to which is given the name of the Central Nervous System, just as the telephone wires all lead into a “central exchange.” ”

“ Our sensory and motor [3] organs are the servants of consciousness; its messengers or scouts; its agents or laborers; and the nervous system is its administrative office. A large part of our anatomical characteristics exists for the purpose of increasing the resources of consciousness, so that it may do its bionomic function with greater efficiency. ”

“ According to certain histological researches of recent years we know that between the sense-organs and the central nervous system there exist closely connected chains of conductors or neurons, along which an impression received by a single sensory cell on the periphery is propagated avalanchelike through an increasing number of neurons until the brain is reached. ”

“ It is no less true that an organ which is not used withers away. If one carries his arm in a sling for several weeks, it grows thin. Now, a sensory organ, like the eye, is simply a mechanism for the reception and transmission to its corresponding part of the brain of appropriate impulses. ”

“ And in the process of specialization the sensorium itself is subdivided into higher and lower nerve centers—centers of conscious thought and automatic transfer of impulse into motion. This transfer indicates the real nature of all forms of nerve action. All are processes of transfer of sensation into movement. The sensorium or brain has no knowedge except such as comes to it from the sense organs through the ingoing or sensory nerves. It has no power to act save by its control of the muscles through the outgoing or motor nerves. ”

“ The retina is sensitive to the light. The light produces chemical changes on the retina. These changes set up an excitation in the optic nerves, which is conducted to a certain place in the brain, causing an excitation in the brain. Now the important point is that when this excitation is going on in the brain, we are conscious, we see the picture.
As far as science can determine, we do not see, nor hear, nor taste, nor smell, nor have any other sensation unless a sense organ is excited and produces the excitation in the brain. There can be no doubt about our primary, sensory experience. ”

“ If we inspect the percept more closely, we find that there is some important difference in the character of the various constituent sensory elements. The central elements forming the nucleus of the percept are given directly by the sense-organ stimulated by its appropriate sensory stimuli, while the subordinate sensory elements are given indirectly,―they cannot be traced to appropriate sensory stimuli exciting those particular sense-organs on the activity of which those subordinate elements depend for their manifestation. ”

“ How is consciousness of these sensations brought about? No doubt, in a manner similar to that of the mediation of such sensations as odors and tones: through the stimulation of sensory neurons and the propagation of nervous processes toward the motor points of the body. The place of stimulation must be somewhere in our organs of nutrition, and thus these organs must be regarded also as a kind of sense organ. That the sensory function can be attributed to an organ in addition to another function has been proved by the example of the skin, muscles, and joints. ”

“ Actions, which were at first performed consciously, become, through habit and association, reflex or automatic—the sensory nerve-cells exciting the motor nerve-cells, without first communicating with those cells on which our consciousness and volition depend. ”

“ In other words the excitation of any sensory organs sets up a series of sensory impulses which are transmitted along the sensory nerve fibres to the brain, where they are referred to the cerebellum or filing case, locating a set of associated impulses which travel outward from the motor area of the brain and result in the actions, or series of actions, which are necessary to produce a word. ”

“ There can be no doubt that many of the lower animals are largely dependent upon senses which are not included in the conventional special sense list. The contention that certain organs which are commonly recognized as sensory in function, the cristæ acusticæ of the ear, for instance, are merely reflex control organs, has little weight in this connection, for every sense-organ is part of a motor control mechanism, and so far as we are able to judge from available evidence each has as an accompaniment of its functioning a mode of sensation. ”

“ Thus this most delicate and difficult course of investigation supports the view that much of the activity of the animal organism is provided for by an established connection between nerve cells respectively presenting the terminus in the brain for a sensory nerve, and the starting point for a motor nerve, or point of communication with such a nerve. From this conclusion, it follows that a very large amount of the activity which we witness in the case of animals, often attributed to instinct, or even to voluntary determination, is to be described as sensori-motor activity. ”

“ This they do by supplying special structures through which the stimuli can act to the best advantage upon the nerve endings. Moreover, there are different kinds of sense organs, and these cause the neurons to be sensitive to different kinds of stimuli. Acting through the sense organs adapted for receiving them, light, sound, heat, cold, and odors all act as stimuli for starting impulses. Indeed, the arrangement is so complete that the nervous system is subjected to the action of external stimuli in some form practically all the time. ”

“ The structure of the other sense organs {256}indicates their adaptation to a tactile function; in each case a nerve traverses the axis of the organ, and the nerve-fibrils terminate in sensory cells. Very probably the palps have a certain power of testing the food—a combination of the senses of taste and smell. ”

“ But we must go farther, and ask whether the skin-nerve is ever motor, and whether the muscle-nerve is ever sensory? To answer this, we must first settle one or two points of physiology and anatomy. A nerve is sensory because it stimulates the Sensibility of its Centre, and not because its termination is in the skin. It is not the nerve which is sensitive, bat the centre. ”

“ When our sense organs are stimulated, the stimulus is conveyed by means of sensory nerves to the brain and there gives rise to sensation, the sense organs are sensitive to various kinds of stimuli, the stimulus to the eyes gives the sensation of sight, to the ears the sensation of sound and so on. ”

“ The complex nature of our higher nervous centres, which is required to bring about the proper adjustments of the infinite variety of our present sensory experiences to appropriate co-ordination with a nearly equal variety of possible muscular combinations, is too common a subject of modern knowledge to need more than mention here. This vast central co-ordination of sensory paths to motor paths has itself become a special function of our neural organism of major importance. ”

“ The several works which these nerves do are called the senses. By means of these sensory nerves we receive impressions from the external world, sensations of heat, cold, roughness, good and bad odors, taste, sound, and the color and form of things. Thus impressions of the external world are made upon the brain, and it is these impressions that stimulate the brain to action. The brain worked on by them, through ways that we know not of, governs the muscles, sends commands by the motor nerves, and rules the body as a conscious, intelligent will. ”

“ The primary elements are initiated directly by incoming peripheral stimulations, while the secondary sensory elements are brought about indirectly, through the mediacy of the primary elements, the secondary elements themselves being really derived from sense-organs others than the ones directly stimulated by the peripheral excitation. ”

“ So far as these experiments go there appear to be at least four sensory factors of importance in the formation of a simple labyrinth habit: the chemical sense, touch, vision and the muscle sense. That the chemical sense and touch are valuable guiding senses is evident from even superficial observation, and of the importance of vision and the muscle sense we are certain from the experimental evidence at hand. ”

“ Those which carry the orders of the mind to the different organs are called the motory nerves; while those which bring back impressions which they receive are styled sensory nerves. If the sensory nerve leading to any part be cut, all sensation in that spot will be lost, while motion will remain; if the motory nerve be cut, all motion will be destroyed, while sensation will exist as before. ”

“ Hence the natural inference has been that inside the organism there is a listener: the Soul is said to listen, transforming excitation into sensation. This inference380 only needs a more systematic interpretation and it will represent the biological theory, which demands something more than the reaction of the sensory organ—namely, the reaction of the whole organism through the sensory organ. I mean, that no organ isolated from the organism is capable of a physiological reaction—only of a physico-chemical reaction ”

“ The whole forms an interlacing feltwork formed of watery nerve cells and processes, and not only receives sensory stimuli and transmits them as motor impulses, but is more or less permanently modified by each sensory thrill which enters it, memorising each, more or less, for longer or shorter time according to its character or intensity. ”

“ The co-excitations of the sensory centers, that are as yet impressed with too few memory-images, can not yet take place on occasion of a single excitation, the cerebral connecting fibers being as yet too scanty. ”

“ The alternative form of the view that assumes partial identity of the anatomical bases of the percept and the representation of an object, would regard the neural correlate of the sensation as the transmission of the nervous impulse throughout the length of the sensori-motor arc of the cortex, from sensory inlet to motor outlet ”

“ The sensory nerve cell, the recipient of the stimulation, like the muscle cell, the reagent to stimuli, has evolved from the primitive cell by greater and greater differentiation, both of structure and function. In the crustaceans, invertebrates, and lower vertebrates where motor reactions to stimuli are more or less complex and varied, the sensory aspect of the moment is probably correspondingly complicated,―organic connections are present giving rise to secondary sensory elements, constituting the material of perceptual life. ”

“ For while the various sensory surfaces are severally adapted to respond to different kinds of external movement—the eye to light, the ear to sound, and so on—any of these surfaces may be brought into suitable relation with any of the muscles of the body by means of the cerebro-spinal nerve-centres and their intercommunications. ”

“ This subject requires to be further investigated, as it probably depends not only on the present or previous plus or minus of the sensorial power of association, but also on the introduction of other kinds of sensorial power, as in Class IV. 1. 1. D; or the increased production of it in the brain, or the greater mobility of one part of a train of actions than another.
Thus when much food or wine is taken into the stomach, if there be no superfluity of sensorial power in the system, that is, none to be spared from the continual actions of it, a paleness and chillness succeeds for a time ”

“ Most of the sensory cells of the animal minister at first to reflex action, and there is thus little true perception. The stimuli which have called forth the reflex action may result afterward in consciousness; but until brain and muscle have reached a higher grade, this could be of but slight benefit to the animal. Perception and consciousness are exercised mainly in the recognition and attainment of food. ”

“ If we suppose the sensory nerves from those parts of the body beneath any patch of skin to terminate in the same sensorial brain-tract as those from the skin itself, and if the excitement of any one fibre tends to irradiate through the whole of that tract, the feelings of all fibres going to that tract would presumably both have a similar intrinsic quality, and at the same time tend each to arouse the other. Since the same nerve-trunk in most cases supplies the skin and the parts beneath, the anatomical hypothesis presents nothing improbable. ”