Excitation

“ When the stimulus is applied on the more excitable half of the organ, the result is a predominant contraction of that half, which cannot be neutralised by the excitation conducted to the less excitable half of the organ. ”

“ Physical Excitation.—If we are disposed to seek dream sources not outside, but inside, the organism, we must remember that almost all our internal organs, which in their healthy state hardly remind us of their existence, may, in states of excitation—as we call them—or in disease, become for us a source of the most painful sensations, which must be put on an equality with the external excitants of the pain and sensory stimuli. ”

“ We have seen that stimulus produces a certain excitatory change in living substances, and that the excitation produced sometimes expresses itself in a visible change of form, as seen in muscle; that in many other cases, however—as in nerve or retina—there is no visible alteration, but the disturbance produced by the stimulus exhibits itself in certain electrical changes, and that whereas the mechanical mode of response is limited in its application, this electrical form is universal. ”

“ It remains for us to obtain data concerning the cycle of excitation processes in the living substances by the aid89 of the combined employment of the most varied kinds of physical as well as chemical indicators. If we use the most varied types of living substance of widely differing properties, showing us the greatest variety of vital manifestations, we may hope by the use of comparative physiological methods, even though with difficulty, to separate more and more the essential details of the general processes of excitation. ”

“ Certain agents induce excitation in living tissues, the excitatory change being detected by contraction, or by electromotive variation, or by change of electric resistance, and in growing organs by the retardation of the rate of growth. ”

“ It is self-evident that in the first instance, in which the stimulus acts on the centrally situated normal stretch, the wave of excitation, thereby set free, must in passing through the affected stretch undergo a decrement of its intensity. ”

“ We know by accurate measurements that the excitation of a nerve lasts much longer than the stimulus, a momentary impact producing an enduring agitation. We know also that the excitation of a centre lasts longer than the muscular contraction it has initiated. We know, moreover, that a nerve may be totally incapable of conducting an external stimulus, yet quite capable of conducting a central stimulus ”

“ We found that when a sense organ is stimulated by its appropriate type of stimulus, this stimulation travels through the sensory nerves and sets up an excitation in the brain. This excitation in the brain gives us sensation. We see if the eye is stimulated. ”

“ The neural process is one continuous excitation along the whole line of ingoing nerve, centre, and outgoing nerve, which nowhere ceases or changes into another process, until the excitation of the muscle introduces a new factor. So long as the excitation keeps within the nerve-tissue, it is one and the same process of change; its issue in a contraction, a secretion, or a change in the conditions of consciousness, depends on the organs it stimulates. ”

“ When an excitation increases, as we have seen, the number of muscular groups set in motion, resistance to transmission increases in the same proportion. “The sensation of pain presupposes a reflex movement and an arrest of nervous conduction in the grey substance of the spinal marrow.” It is this process of inhibition, in varying degrees, which is felt by the consciousness as pain.
2. Vascular reflexes.—Peripheral excitation also has reflex effects on the vaso-motor system; it produces contraction of the spinal arteries, of the carotids, and of the cerebral 85arteries. ”

“ The result of excitation, or if one will, of stimulation of a living part, can, therefore, according to circumstances, be either merely a functional process, or there can be a more or less intense nutritive activity produced without the function being necessarily at the same time activated, or finally, it is possible11 that a process of formative change may occur which produces new elements in greater or less numbers. ”

“ If the various intensities of stimulation always bring about excitation of the same strength and we see in spite of this that various intensities of stimulation produce various kinds of effects, then we must think of the possibility that various intensities of stimulation bring about some other effect than that of variations in intensity in the course of the wave of excitation. In this connection variations in the time involved must be taken into consideration. One might think that strong stimuli may develop a longer wave of excitation than such of weak intensity. ”

“ Bose next pointed out that there remains, for every response, a certain residual effect. A substance, which has responded to a given stimulus, retains, as an after-effect, a 'latent impression' of that stimulus and this 'latent impression' is capable of subsequent revival by bringing about the original condition of excitation. The impress made by the action of stimulus, though it remains latent and invisible, can be revived by the impact of a fresh excitatory impulse. ”

“ Nervous excitation always tends to beget muscular motion; and when it rises to a certain intensity, always does beget it. Not only in reflex actions, whether with or without sensation, do we see that special nerves, when raised to a state of tension, discharge themselves on special muscles with which they are indirectly connected ”

“ Although there is still a good deal of uncertainty respecting the exact composition of the feelings of movement, it may be taken as fairly proved that they include an active element or "feeling of innervation," which is correlated with the central excitation of motor fibers, and a passive element or tactual sensation which is connected with a reflex excitation of sensory fibers, consequent on certain differences in the tensions and mutual pressure of various parts of the skin which result from the movement. ”

“ Without depression no excitation can take place in the vital activity of the organism, for, as we have seen, every excitation is secondarily followed by a refractory period. To this must be added the great number of primary depressions, directly brought about by the most varied stimuli, such as cold, want of oxygen, poisons, etc., without the presence of a preceding excitation. ”

“ In a word, each excitation, according to its energy, produces more or less extensive movement which may be limited to a single group of muscles. It is not so with a frog in which the spinal cord is unsevered; the movements which succeed a stimulus, whether it be strong or feeble, are always movements of the whole body. ”

“ The Reflex Theory asserts that when a sensory nerve is stimulated, the excitation of the centre may either subdivide into two waves, one of which passes directly to the brain and there awakens sensation, the other passes over to the motor-roots and causes muscular contractions ”

“ Every stimulus induces motion only as a result of polar excitation. Every stimulus polarizes; for even the gentlest contact is like the friction, and produces electrical antagonism. It therefore amounts to the same, whatever stimuli, whether mechanical, chemical, or spiritual, have been applied to the muscle. One acts like the other. ”

“ It is very simple; all that is required is a counter excitation of the nerve, and we have with us to-night what any person who cares to consider the subject can employ at any time, and thus behold an outline of a part of his own brain. ”

“ In accordance with the three groups into which general vital phenomena are divided, it follows as a matter of course that the excitation or depression produced by a stimulus can manifest itself in the cell's metabolism, assumption of form, and manifestation of energy. The effects of excitation upon the production of energy are the most striking, and were therefore in former times frequently thought to have a claim par excellence to rank as stimulating effects. ”

“ This is the secondary extension of the result of stimulation from the part of a living organism directly and primarily affected by the stimulus, to the surrounding structures. All living substance has the capability of conducting an excitation, which is produced locally through a catalytic stimulus, to a neighboring part, not directly affected by the stimulus. It finds its highest development in the nerve, but in no living structure is it completely absent. ”

“ In the one experiment we see simultaneous excitation in the same centre and the same direction. In the other simultaneous excitation in different centres. The more powerful excitation suppresses the discharge from the less powerful ”

“ This excitation of the nerve can, however, be induced by very different kinds of processes, namely, by all processes which possess in common the condition that they suddenly increase certain disintegration processes in the living nerve substance. ”

“ The intellectual or idea function, the thinking and working function of the mind, may be supposed to depend on the intercommunication of the nerve cells or centres of the entire hemispheres, carried on by means of the nerve-fibres, this interaction being accompanied by a feeling or emotion peculiar to the centres acting, but which varies according to their physical state at the moment of excitation, or that produced by the excitation itself. ”

“ I know, if I know anything, that a certain amount of physical energy is involved in every instance of nervous excitation, and that the influence of this energy acting upon matter is easily communicated to, and will act upon, willing subjects. ”

“ A given stimulus will bring about an intense excitation, and the ‘down’ D-change will therefore be very much greater than the A-change. Let us now consider the case at the opposite extreme where, owing to unfavourable condition, the ex­cit­abil­ity is at its lowest. Under stimulus the excitatory D-change will now be relatively feeble compared to the A-change, by which the potential energy of the system becomes increased. In such a case successive stimuli will increase the functional activity of the tissue, and bring about staircase response. ”

“ Now we should like to know, above all, what conditions cause the creation of pleasure and pain, but here we fall short. We may only venture to say that pleasurable excitation in some way involves lessening, lowering or obliterating the amount of stimuli present in the psychic apparatus. ”

“ Then, under the influence of a sympathetic emotion or of irritation, a kind of nervous excitation is communicated from one to another among all those who are assisting; curious symptoms appear among the magnetized persons. ”

“ I have in the preceding paragraph described an experiment where under a given intensity and duration of exposure the excitations of the proximal and distal sides bring about neutralisation, the organ assuming a dia-phototropic position. If the intensity or duration of the stimulating light be further increased, it is easy to see that while excitation transmitted to the distal side is being increased, the excitatory contraction on the proximal side may, at the same time, be decreased owing to fatigue brought on by over-stimulation. ”

“ The external excitations are merely the clues. The internal apparatus is set vibrating in a constant manner if no other external or central stimulus is present to demand other adjustments or to intensify the same kind. When such synergetic or antagonistic stimuli are also present the mutual influences of feelings do seem to be, indeed, of great significance. ”

“ All which the excitation of that portion of brain where the emotion of power may have its center can effect is certain movements which such an emotion would cause when irritated.
To arrive, then, at the demonstration of centers of ideation there is but one way:
1. We must observe the physical expression of our thoughts and feelings, as far as possible; in other words, we must study the outward visible signs of their manifestation.
2. We must take the limbs and muscles, which are affected by definite emotions, and see on what occasions they are made to move by central excitation. ”

“ If we disregard the distinction between mind and body, we may say that the stimulus for a response may be an idea as well as a perception, the perception arising from the immediate stimulation of a sense organ, and the idea arising from an excitation of the brain not caused by an immediate stimulation of a sense organ.
Instincts and Habits. In human action it is evident that there is always a stimulus to start the nerve-impulse which causes the action. If we make inquiry concerning the connection between the stimulus and response ”

“ ALL our sensations, from the most trifling pleasure to the highest delight, from the hardly perceptible discomfort to the keenest anguish, the whole gradation of manifold variations of feeling, originate from the propagation of excitations from without through the nerves to the central organ of the nervous system and to consciousness. ”

“ In how far those sudden and violent excitations of the autonomic nervous system which accompany strong emotions are due to the intervention of the glands of internal secretion, and in how far they depend upon direct neural conduction from the brain, we are as yet but ill-informed. ”

“ For the sake of illustration, we may suppose that the greatest excitability of which the living body is capable is 80 degrees: this may be supposed to be the excitability possessed by the body at the commencement of its life, because no part has then been wasted or exhausted by the action of stimuli. Now, if we suppose a scale of excitability to be formed, and divided into 80 equal parts or degrees, the excitability will be wasted or exhausted in proportion to the application of stimuli, from the beginning to the end of the scale. ”