CHAPTER IV.
BREATHING FURTHER CONSIDERED THEORETICALLY AND PRACTICALLY.
When one takes into account the large number of muscles employed in respiration, and remembers that these muscles must act in perfect harmony with each other if the great end is to be attained, he naturally inquires how this complex series of muscular contractions has been brought into concerted action so as to result in that physiological unity known as breathing.
It is impossible to conceive of such results being effected except through the influence of the nervous system, which acts as a sort of regulator throughout the whole economy. All the parts of the respiratory tract are supplied with nerves, which are of both kinds—those which carry nervous impulses or messages from and those which convey them to the nervous centres concerned; in other words, to and from the bodies of the nerve-cells whose extensions are termed nerves. These centres are the central offices where the information is received and from which orders are issued, so to speak.
The chief respiratory centre—the centre—is situated in that portion of the brain just above the spinal cord, in its continuation, in fact, and is known as the medulla oblongata, or bulb. But while this is the head centre, at which the ingoing (afferent) impulses are received and from which the outgoing (efferent) ones proceed, it makes use of many other collections of nerve-cells, or subordinate centres—e.g., those whose nerve-extensions or nerve-fibres proceed from the spinal cord to the muscles of respiration.
Fig. 15. The purpose of this diagram is to indicate the relation between ingoing (afferent) and outgoing (efferent) nervous influences (impulses)—in other words, to illustrate reflex action. The paths of the ingoing impulses are indicated by black lines, and those of the outgoing ones by red lines, the point of termination being shown by an arrow-tip. The result of an ingoing message may be either favorable or unfavorable. The nervous impulse that reaches the brain through the eye may be either exhilarating or depressing. The experienced singer is usually stimulated by the sight of an audience, while the beginner may be rendered nervous, and this may express itself in many and widely distant parts of the body. An unfavorable message may reach the diaphragm or intercostal muscles, and render breathing shallow, irregular, or, in the worst cases, almost gasping. The heart or stomach, even the muscles of the larynx, the limbs, etc., may be affected, and trembling be the result. On the other hand, the laryngeal and other muscles may be toned up, and the voice rendered better than usual, as a result of applause—i.e., by nervous impulses through the ear—or, again, by the sight of a friend. Even a very tight glove or a pinching shoe may suffice to hamper the action of the muscles required for singing or speaking. All this is a result of reflex action—i.e., outgoing messages set up by ingoing ones—the "centre" being either the brain or the spinal cord. From all this it is evident that the singer or speaker must guard against everything unfavorable, to an extent that an ordinary person need not. The stomach, as the diagram is also meant to show, may express itself on the brain, and give rise, as in fact it often does, owing to indiscretion in eating, to unpleasant outward effects on the muscles required in singing or speaking. Of course, no attempt has been made in the above figure to express anatomical forms and relations exactly.
When all the ingoing impulses from the lungs, etc., are cut off, if respiration does not actually cease, it is carried out in a way so ineffective that life cannot be long sustained. It follows that as the muscular contractions necessary for the chest and other respiratory movements are dependent on the impulses passing in from the lungs, etc., breathing belongs to the class of movements known as reflex—chiefly so, at all events. It will thus be seen that respiration is a sort of self-regulative process, the movements being in proportion to the needs of the body. The greater the need for oxygen, the more are the nerve-terminals in the lungs and the centre itself stimulated, with, as a result, corresponding outgoing impulses to muscles.