Regulation of Respiration. Nervous Control of Breathing

The mechanism of regulation of respiration is very complex. Sche­matically it is as follows. In the medulla oblongata there is the respi­ratory centre. In the respiratory centre both excitation and inhibition continuously alternate. When excited it transmits impulses to the spinal cord and hence along nerves to the respiratory muscles; the latter contract and an inhalation takes place. When the respiratory centre is in a state of inhibition the transmission of impulses to the respiratory muscles ceases, the muscles relax and an exhalation re­sults.

The specific stimulus of the respiratory centre is carbon dioxide. As soon as the blood accumulates a certain amount of carbon dioxide, the respiratory centre becomes excited and an inhalation takes place. During inhalation the lungs expand, which stimulates the endings of the vagus nerve embedded in the tissue of the lungs. While arising in the recep­tors the exeitation is transmitted along the vagus nerve to the respira­tory centre and inhibits it, and an exhalation results. Thus respiration is automatically regulated; an inhalation stimulates an exhalation, and the exhalation brings about an accumulation of carbon dioxide which stimulates an inhalation.

116 ♦ Learning to Understand a Medical Text

Respiration is subjected to the control of the cerebral cortex; this being demonstrated by the fact that a person can voluntarily hold his breath for a very short time or change both the rate and depth of respiration. Corti­cal regulation of respiration is also evident in the acceleration of respira­tion during emotional states. Protective acts, such as coughing and sneez­ing, are associated with respiration. Both of them are performed reflexly; the centres of the reflexes are situated in the medulla oblongata.

Nervous control of breathing. The muscles of breathing have no inde­pendent or automatic rhythm, they contract only responding to impuls­es from the brain down the spinal cord. These impulses arise and are coordinated in a specialised area in the brain, the respiratory centre, which is in the medulla. The medulla is at the base of the brain and is a bulbous continuation of the spinal cord within the skull. The respiratory centre has to adjust the volume of air breathed and to maintain a uni­form alkalinity of the blood; the centre effects the reciprocal alteration both of inspiration and expiration.

Упражнение 4. Прочтите данные суждения. Найдите в тексте В предложе­ния, более полно выражающие мысль суждений, и прочтите их.

1. In the respiratory centre excitation and inhibition alternate. 2. Dur­ing inhalation the lungs expand. 3. Respiration is automatically regulated. 4. The cortical regulation of respiration is evident. 5. Protective acts are performed reflexly. 6. The muscles of breathing contract responding to impulses from the brain.