Vestibular system

“ In learning to walk we judge of the distances of the objects, which we approach, by the eye; and by observing their perpendicularity determine our own. This circumstance not having been attended to by the writers on vision, the disease called vertigo or dizziness has been little understood.
When any person loses the power of muscular action, whether he is erect or in a sitting posture, he sinks down upon the ground; as is seen in fainting fits, and other instances of great debility. Hence it follows, that some exertion of muscular power is necessary to preserve our perpendicular attitude. ”

“ Along with the semicircular canals is a structure known as the vestibule which registers the position of the head, and so indirectly of the body, when no movements are being made. We are not ordinarily conscious of the working of these senses; they carry on their guidance of muscular movement without our attention. We can, however, pay attention to what they show if we wish. For example, one who is swimming under water is never in doubt as to whether his head is turned up or down, even though his eyes may be shut. ”

“ The neural connections of the vestibular organ consist of numerous chains of neurons, reciprocally linked in many ways and having their synapses in various anatomical nuclei. All the chains work in intimate collaboration, and the final pattern of reflex responses is attributable largely to the highly complex integrating activity of the center. ”

“ The auditory nerve arises close behind the ventral division of the trigemino-facial root. The root of the auditory nerve encloses a large auditory ganglion. A vestibular nerve arises from the anterior end of the auditory ganglion and passes into the ear capsule, innervating the upper part of the utriculo-sacculus and the ampullae of the anterior and horizontal canals. From the posterior part of the ganglion nerves pass to the ventral part of the sacculus and the ampulla of the posterior canal. Trace these branches as thoroughly as possible. ”

“ Hence children are at first delighted with these kinds of exercise, and with riding, and failing, and hence rocking young children inclines them to sleep. For though in the vertigo from intoxication the irritative ideas of the apparent motions of objects are indistinct from their decrease of energy: yet in the vertigo occasioned by rocking or swinging the irritative ideas of the apparent motions of objects are increased in energy, and hence they induce pleasure into the system, but are equally indistinct, and in consequence equally unfit to balance ourselves by. ”

“ We need only suppose that when the head turns in the plane of any one of them, the relative inertia of the endolymph momentarily increases its pressure on the nerve-termini in the appropriate ampulla, which pressure starts a current towards the central organ for feeling vertigo. This organ seems to be{76} the cerebellum, and the teleology of the whole business would appear to be the maintenance of the upright position. If a man stand with shut eyes and attend to his body, he will find that he is hardly for a moment in equilibrium. ”

“ Thence he traced his "medullary action" downward and backward into the cerebellum, which he supposed to be the center of volition; from this "it descends through the posterior columns of the spinal marrow, and expands through the posterior fasciculi of all the nerves, which are, therefore, the nerves of volition, toward the muscular system." ”

“ And there is the true brain vertigo—a common symptom of disease of the nervous system. In anæmia, and one or two diseases of the heart, giddiness is common—due to the brain not being sufficiently supplied with blood. Here you have the cause of vertigo in a nutshell. To tell which of them is causing your giddiness, with nothing whatever to guide us to a conclusion, is quite impossible.
Foolish.—The pseudonym you have chosen is very appropriate. You are exceedingly foolish to take drugs of which you know nothing; but it is worse than foolish, it is criminal. ”

“ With these increased irritative motions of vision, I suppose those of the stomach are performed with greater energy by direct sympathy; but when the rotatory motions, which produce this agreeable vertigo, are continued too long, or are too violent, sickness of the stomach follows; which is owing to the decreased action of that organ from its reverse sympathy with the increased actions of the organ of vision. For the expenditure of sensorial power by the organ of vision is always very great, as appears by the size of the optic nerves ”

“ Whence though a certain quantity of vinous spirit stimulates the whole system into increased action, and perhaps even increases the secretion of sensorial power in the brain; yet as soon as any degree of vertigo is produced, it is a proof, that by the too great expenditure of sensorial power by the stomach, and its nearest associated motions, the more distant ones, as those of vision, become imperfectly exerted. ”

“ DIAGNOSIS.—Vertigo is of course, as a rule, only a complex symptom of one or more numerous conditions. Acute isolated fits of vertigo are sometimes puzzling, because epilepsy may be preceded by brief vertigo and exist without notable spasms. Time may bring to us a frankly expressive epilepsy to explain former and less distinct fits. But usually it is the attacks of vertigo which are the causes of doubt. A man has sudden giddiness, and falls unconscious for a moment. These attacks persist. How shall we know them as vertigo? how be secure that they be not some form of the lesser epilepsy? ”

“ Permanent vertigo of quite severe character may arise from astigmatic defects, and from almost any form of disorder affecting steadily the power of the eye to accommodate itself to distances; but simple myopia of moderate grades, excessive one-sided myopia, or presbyopia is unlikely to do so. Oculo-motor troubles, paralytic or spastic, are very effective causes of vertigo, which is sometimes quite promptly producible by the wearing of a prism on one eye or by the use of glasses which over-correct, or if exact are for some reason badly borne. ”

“ Let it be stated here that the peculiar role played by the larynx in hearing, already referred to by us in Chapter XVI, is one of the symptoms which tells of the participation of the muscular system in the internal acoustic process.
Psychologically, the difference between ear and eye is that aural perceptions work much more directly on the human will - that is, on the part of our astral organization connected with the limb system. Whereas eye-impressions stimulate us in the first place to think, ear-impressions stimulate us to ... ”

“ This cavity is hollowed out in dense bone, and consists of three parts; the vestibule (a) , or ante-chamber, which is connected with the other two; the cochlea (b) , or snail's shell; and the three semicircular canals (c) . The manner in which the nerve of hearing is distributed is remarkable, and is peculiar to this nerve. In the vestibule and the canals its fibres are spread out over the inner surface, not of the bony cavity but of a membranous bag, which conforms to and partially fills that cavity; and which floats in it, being both filled and surrounded with a clear, limpid fluid. ”

“ The human ear would seem to present greater difficulties. For the essential part of the sense-organ, in this case, is the membranous labyrinth, a bag of complicated form, which lies buried in the depths of the floor of the skull, and is surrounded by dense and solid bone. Here, however, recourse to the study of development readily unravels the mystery. Shortly after the time when the olfactory organ appears as a depression of the skin on the side of the fore-part of the head, the auditory organ appears as a similar depression on the side of its back part. ”

“ The vertigo visualis is owing to less perfect vision, and is not accompanied with pleasurable sensation. This frequently occurs in strokes of the palsy, and is then succeeded by vomiting; it sometimes precedes epileptic fits, and often attends those, whose sight begins to be impaired by age. ”

“ This will be understood by looking at the profile of the interior of the right hemisphere, on which we see the position of the pons and the medulla and their relation to the cerebrum by their ascending fibres. As these ascending fibres correspond to a position just above the cavity of the ear, and as they are the channels of all muscular impulses, the reader will perceive that breadth of head immediately above the cavity of the ear must be associated with muscular impulsiveness. ”

“ Through it the auditory nerve leaves the cranial cavity and enters the ear. The ramus vestibularis leaves through the dorsal part of the hole, the ramus cochlearis through the ventral.
The cavity of the auditory or periotic capsule communicates with the exterior by a fairly large hole, the fenestra ovalis, which lies between the opisthotic and pro-otic, and opens into a deep depression, the tympanic cavity, which is seen in a posterior view of the skull lying just external to the exoccipital. ”

“ To an observer looking at both eyes the left will seem to squint. Of course this continued and extreme rotation produces afferent feelings of rightward motion in the eyeball, which momentarily overpower the faint feelings of central position in the diseased and uncovered eye. The patient feels by his left eyeball as if he were following an object which by his right retina he perceives he does not overtake. All the conditions of optical vertigo are here present: the image stationary on the retina, and the erroneous conviction that the eyes are moving. ”

“ With respect to the Eustachian tube, its aperture into the throat seems indispensable to hearing; and whenever closed, from malconfirmation or disease, deafness is the certain consequence.
The third division of the organ is the internal ear, which is called the labyrinth; it is divided into the vestibule, three semicircular canals, and the cochlea: the whole are incased within the petrous portion of the temporal bone. The internal ear may be considered as the actual seat of the organ ”

“ Sensation, volition, memory, judgment, sight, hearing, and all other sensations are lost by the removal of the cerebral hemispheres. The mobility of the iris is destroyed, not by the removal of the hemispheres, but of the corpora quadrigemina. If the cerebellum be cut away, a bird can no longer jump, walk, or retain its natural position, but it can move and live. When the medulla oblongata, or medulla spinalis, or the nerves of these parts, have been divided, muscular contraction ceases, and all power of movement is lost. ”

“ The DURATION of other forms of vertigo it is less easy to predict. Ocular vertigoes get well soon after the eye trouble is corrected, and the like is true of most vertigoes due to peripheral causes. So also the giddiness which is sometimes seen as a very early symptom in locomotor ataxia is transient, and will be apt, like the ocular and bladder troubles which mark the onset, to come and go, and at last to disappear entirely. It is to be remarked that vertigo at the beginning of posterior sclerosis is common, and is not due to ocular motor conditions. ”

“ But the primary use of this tube is to afford a free communication between the middle ear and the external atmosphere, and thus secure an equal pressure upon both sides of the membrane of the drum of the ear, however the density of the atmosphere may vary. If, from undue tension of the membranes, pain is experienced in the ears, when ascending into a rare atmosphere, as in a balloon, or descending into a dense one, as in a diving-bell, it may be relieved by repeating the act of swallowing, from time to time, in order that the inner and outer pressure may thus be promptly equalized. ”

“ Excessive stimulation of the canals gives the sensation of dizziness.
The otolith organs in the vestibule are probably excited, not by rotary movements, but by sudden startings and stoppings of rectilinear motion, as in an elevator; and also by the pull of gravity when the head is held in any position. They give information regarding the position and rectilinear movements of the head, as the canals do of rotary head movements. Both are important in maintaining equilibrium and motor efficiency.
The muscle sense is another sense of bodily movement ”

“ The great opponent of such action is the stiffening of the cords of the neck—the muscles on the sides of the neck. In connection with the work to be looked after in the third department, yet to come, the way of removing that stiffness will have mention. Within the larynx there are many delicate muscles which are performing their various functions. What they do, and how they do them has been the subject of study through several generations and the question is not solved. An eminent physician has for several years been photographing throats while producing tone. ”

“ PROGNOSIS.—In true vertigo, if we exclude the organic causes, and especially intracranial neoplasms, there is very little to be feared. Deaths have been seen in Menière's disease, but are most rare. Even in grave examples of labyrinthine vertigo there is a probability that the worst which can occur will be deafness, and that vertigo will gradually cease as the delicate neural tissues become so degenerated as to cease to respond to irritations. ”

“ The disorder that leads to vertigo implies a retention of a measure of the normal function of the internal ear, and therefore of hearing, whereas the disease that has caused complete destruction of the internal ear and consequent loss of hearing has equally destroyed the function of the labyrinth in maintaining a sense of balance, and has obviated the aural sensations of equilibrium and loss of balance. ”