The Parents' Review

A Monthly Magazine of Home-Training and Culture

The Child's Nerve-Mechanisms.

The nervous system of the human body is at once important and complicated; it is important because through it we reach all the other systems of the body, and the manifestations of what we call Mind are made possible; it is complicated both in its structure and its mechanism. The rational rearing of children demands some knowledge of the mode of growth and action of this system. Recognising education as fundamentally a directing, stimulating and strengthening of physical and mental physiological processes in course of development, I propose to draw attention in this article to a few elementary facts in the physiology of the nervous system which may be usefully added to the parent's stock of knowledge.

To commence rationally let us look at the nervous system of the newly-born infant. Like much of the rest of the body this system is imperfectly developed at birth; some parts of it are anatomically imperfect, and other parts, although anatomically perfect, are feeble and unable to immediately assume their functions. The chief part which is really anatomically imperfect is the cerebrum, that part of the brain whence psychical activity springs--whence mind and will exert their control over the body. The infant cerebrum has been aptly compared to the simple telegraphic system of a small town, bringing the few leading inhabitants into communication; while the developed adult cerebrum resembles the telegraphic and telephonic systems of a large city; with the difference that the excess of nerve cells and fibres in the adult over those in the infant is beyond estimation. We can understand then that will and thought are impossible in the infant, seeing that the organ from which they spring is undeveloped. The "special sense-organs" (i.e., the eye, ear, nose, &c.) are examples of the parts which are structurally complete but functionally feeble in the earliest days of the child's existence; this subject I will refer to later, merely stating meanwhile that in the strictest sense an infant cannot see, hear, or smell.

The absence of the power to will or think, and the incapability to see or hear properly being granted, the question naturally arises, how is it that an infant can cry and move, actions which one might be justified in considering as signs of consciousness and evidence of sight and hearing?

The answer is that these acts, and every other act of the human infant, are performed by means of a physiological mechanism known as reflex action. Now, what is reflex action? What is this mechanism by which acts are performed without the influence of the cerebrum--in other words without voluntary activity?

Could we experimentally remove the infant's cerebrum and then demonstrate the occurrence of reflex action, further evidence of its existence would be unnecessary. Though this is obviously impossible in the human being, it can be done in animals, and physiologists have proved beyond a doubt by experiment that the higher parts of the brain have no concern in reflex action. By reflex action it is meant that a certain kind of nerve, called a sensory nerve, receives a stimulation; that this stimulation sets up an impulse which is conveyed along this sensory nerve to a nerve-centre (a collection of nerve-cells situated in the spinal cord or lower part of the brain); and that in this centre the sensory impulse becomes a motor one, and is carried down one or more motor nerves to stimulate certain muscles into certain actions.

Take now an infant's motor act, and see how this can be produced reflexly. Let the act be that of coughing; the impulse to cough may, like most reflex actions, proceed from several surfaces, e.g., some part of the mucous membrane of the respiratory tract (throat, windpipe, bronchial tubes, and lungs), the stomach (hence the stomach-cough of dyspeptics), or even the skin, when a surface of it is exposed to sudden stimulation by a draught of cold air. This impulse proceeds up the sensory nerve to the coughing centre, situated in a part of the central nervous system called the medulla oblongata, and thence the motor impulse at once proceeds down the nerves of expiration to set up the violent expiratory act which constitutes coughing (vide A, B, C, in diagram). The essential characteristic of pure reflex action is its entire independence of the will. Although the infant's acts are all reflex at first, it must not be thought that reflex action is confined to the infant; older children and adults are

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constantly showing evidence of it--it is probably the busiest nerve-mechanism in the body. In the April number of this magazine Dr. John Mason pointed out how susceptible the infant's centres are, and how liable an impulse to a centre is to overflow to other centres and set up other motor acts. We may presume, however, that a moderate sensory impulse will, in the infant, under ordinary circumstances, set up no more than a correspondingly moderate motor act. With the further development of the cerebrum Nature provides a power to voluntarily control reflex actions, at the same time that the will itself becomes able to originate motor acts; what are called psycho-motor centres are developed, and we may also assume the development of centres with a power of inhibition. There are some reflex actions which cannot at any time be performed by volition as well; over these inhibition has no power; the will can neither originate nor control them. We are not concerned with these at present, but rather with those actions which can be performed either reflexly or voluntarily; these can also be inhibited by the will. This inhibition, this power of controlling reflex acts in course of performance, has its limits, for if the sensory impulse originating the reflex is very strong or is frequently repeated, the will is unable to control or prevent the discharge of the motor act. Look once more at the act of coughing, this time in an older child or adult in whom the cerebrum and will are developed. Coughing, as shown, usually arises reflexly from one of several surfaces, but it may rise voluntarily; witness the cough given to attract a person's attention. It can also be inhibited voluntarily; thus, we feel a tickling in the throat, and the impulse sets up the cough as described; if we are placed in such circumstances that we are anxious to maintain absolute silence--e.g., listening for a distant sound--we call our volition into play, and an impulse from the cerebrum promptly stimulates the inhibitory cells to prevent or modify the act by sending down an inhibitory impulse to the coughing centre (vide diagram). If, however, the throat-tickle is severe, or tickle follows tickle in rapid succession, the voluntary control is over-powered, and we cough in spite of all. There is another way in which we sometimes may try to inhibit the cough or to aid the cerebrum in inhibiting it, viz., by biting our lips or our tongue; this acts by stimulating strongly a sensory nerve, which stimulation runs directly to the inhibitory cells; for clearness sake, we suppose the existence of a special inhibitory centre connected with the reflex centre, the cerebrum, and the sensory nerve (vide diagram). This power of voluntary inhibition is important to be remembered, because without exercising it we may allow reflexes to become excessive, or develop into habit. The majority of coughs heard in church or schoolroom could easily be controlled; some are certainly wholly or partly genuine uncontrollable coughs, whose owners have no business to be present in a public assemblage; others are habit or imitative coughs, which would not occur were the owners' minds centred on the subject before them. The fault here may lie with the owner who has allowed his reflex to become a habit, or with the preacher or schoolmaster who is unable to engage the attention of his audience sufficiently to make them voluntarily control their coughing reflexes. There are fewer coughs heard in the church of an eloquent and powerful preacher when he occupies the pulpit himself than when his curate of feeble intellect is holding forth.

The theory that there are special groups of nerve-cells acting as inhibitory centres is a sufficient one; inhibition has been explained on other more physical lines, however, but this does not concern us. Moral self-control is nothing more or less than a development of inhibitory centres. The child, with his growing cerebrum, requires moral inhibitory centres to be developed; here lies a great parental function--to assist in this development. The parents who make their inhibitory centres the centres on which their children have to rely are guilty of a serious error; they exercise their authority and dictate, instead of superintending and stimulating the gradual growth of the child's own inhibitory centres. Thus we see severe and authoritative parents dispatch their sons into the world to speedily disgrace themselves by want of self-control and mental balance, and to end by being sent off to the colonies or elsewhere, "fit for nothing else." There is to this sad fact the consolation that, given a fairly good "fibre," this kind of youth frequently develops his own inhibitory centres while he "roughs it," and turns out a useful member of society. The child uneducated in inhibitory power may develop in another direction from this; he becomes a gentle, amiable young man, with a touching freedom from wilfulness and naughtiness, but feeble and of undecided character--the "good young man who died" of the song; a looker-on or a loser in life's race. Our public schools and Universities are of immense benefit in developing inhibitory centres in the British youth; frank, open, self-reliant youths often are formed here from the poorest material that the mother's apron-string can furnish. All this is no doubt an old story, but I trust I have shown its analogy and its basis in physiological fact. There are other influences affecting the development of moral inhibitory centres, such as heredity and constitutional delicacy, which I will not at present touch upon.

There is another variety of the reflex mechanism from which we can draw a lesson--a process known as summation of stimuli; this means shortly that although one sensory stimulus may not suffice to set up the reflex act, several similar stimuli repeated may bring it about; one little tickle in the throat may fail to produce a cough, while several similar little tickles in succession become "summated" in the centre and succeed. A story told by Dr. Andrew Coombe illustrates this so well in moral action that I may be excused if I quote it in full.

"A respectable-looking woman made some purchases in a shop in town, in payment of which she tendered a five-pound note. The clerk on examining it refused it as forged. The poor woman took it back with some surprise and offered over another. It also proved to be forged. The woman was handed over to the police, and an inquiry was instituted by which it was ascertained that she had been for several years in the service of a country gentleman, who gave her a high character. About a year before, she first saw two five-pound notes lying unconcealed among some old papers in her master's room, where they continued undisturbed for month after month as if forgotten by him. For a long time she never thought of touching them; at length the desire to appropriate them arose in her mind, as she believed they would never be missed. After resisting the impulse for months, the desire increased so much by the daily stimulus of the object which excited it that she at last yielded and subjected herself for the first time in her life to the degrading consciousness of guilt. Afraid of detection she made no use of the notes for some time, but reserved them for the purchase referred to. The gentleman had known the notes to be forged, and allowed them to remain undisturbed."

How beautifully we here see the impulse to appropriate set up by the sight of the notes, running to the woman's cerebrum and being for months held back by her inhibitory centres; but this impulse obeys rigidly the law of summation of stimuli; summation takes place and appropriation of the notes results in spite of the (presumably weak) inhibitory centres. The responsibility of the gentleman who left the notes so carelessly exposed may be pointed out in passing.

An instance of summation of stimuli may be seen any day in our crowded streets; the cunning beggar in pursuing the hurrying passenger with insinuating demands is summing up stimuli as he pursues, and the passenger is merely obeying the law when he at last discharges the copper! The beggar's cunning is physiological! The passenger's weak-minded compliance is physiological!

We now turn to the special senses whose organs I have explained are structurally complete, but functionally weak in the infant. Each special sense organ is limited in its power to receive impressions; it is adapted to receive only the impulse of particular stimuli--thus light is the special stimulus pertaining to the eye. In the new-born infant the eye is too feeble to take on its function at the outset; and the cerebrum being, as before explained, of very simple structure, its part concerned in the conscious perception of light is undeveloped, and so even if the optic nerve were able to carry up an image it could not be seen. The baby newly born takes no notice of an object, however bright, held to its eyes; a few days elapse before he even gazes blankly at it, as if the complicated sense was being awakened, and a month or two before his eyes follow an object as if at last he saw. Similarly with the sense of hearing, although from the very first the infant may cry at sudden or loud sounds, it takes weeks, even months, before he is able to localise a sound--turn his head in the direction of the sound. The infant's cries at a sudden alarm can be understood on the principle of reflex action. How frequently we hear a thoughtless mother or ignorant nurse scolding so harshly and loudly the poor little four-year-old that baby in the cradle is awakened and screams from the excessive stimulation of his auditory nerves.

When we recognise how gradual is the growth of the sense organs and the senses, we see how important it is that for their proper development proper stimuli should be applied to them in a systematic and gradual way; for, although the child may follow an object with his eyes, indicating that he sees it, it does not follow that the finer adjustments (to borrow a phrase from microscopy) of his eyesight are developed; that, for instance, he can appreciate the size, shape, and colour of the object; this comes gradually and all the more surely for simple beginnings and systematic strengthening and education. No part of the child's body--and this has been insisted on hundreds of times before--be it cerebrum, special sense organs, nerves, muscles, lungs, or stomach, should ever have excessive or too complicated stimuli, appropriate or not, applied to it when quite unable to receive them with benefit to itself and the rest of the body. It is as absurd to hang a complicated battle-scene or an old master in the nursery with a view to educating the child's artistic sense of object and colour before he has been taught even to recognise the primary colours and kindred elements, as to give it meat to eat before its teeth are developed and the stomach capable of digesting such food.

We have looked at the mechanism of reflex action, the important power of inhibition, the summation of stimuli, and the special senses and organs as they are in the infant and the growing child; there is left the cerebrum and with it mind and will, into which it is beyond my present province to enter. The bare statement already made that in the infant these are undeveloped and in the child are growing is immensely suggestive; what a field is open here for the parent! The task lies in striking the via media between allowing perfect freedom and unchecked indulgence, and so developing the unregulated cerebrum of a "spoilt child," or making rigid rules to cramp and stunt cerebral growth, yielding a child with want of self-reliance and a broken spirit. This is always a responsible and difficult task; but to the parent starting with the premises that education is a directing, stimulating, and strengthening of natural processes, that his duty is to superintend the fulfilment of law--moral law, social law, and physiological law--and if he is willing with Emerson to "accept the hint of each new experience," it is never a hopeless one.

Typed November 2014