Identifier: physiologybioche00macl (find matches)
Title: Physiology and biochemistry in modern medicine
Year: 1918 (1910s)
Authors: Macleod, John James Rickard, 1876-1935 Pearce, R. G. (Roy Gentry), 1884-
Subjects: Physiology Biochemistry
Publisher: St. Louis : Mosby
Contributing Library: Columbia University Libraries
Digitizing Sponsor: Open Knowledge Commons

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he most successful experiment lias been performed as follows:The influence of the higher nerve centers was removed by cutting acrossthe peduncles of the cerebrum or the pons. The influence of afferent im-pulses traveling up the spinal cord was removed by completely severingthe spinal cord below the level of the phrenic nerves and sectioning allthe posterior or sensory spinal roots of the cervical cord above the levelof this section. The vagi were also cut to remove the impulses traveling 330 THE RESPIRATION by them to the respiratory center. By such an operation the only lowerrespiratory neurons left intact are those of the phrenic nerve, so that therespiratory movements that alone are possible are those in which thediaphragm participates and the muscles of the alae nasi and larynx. Itwas found that the animal after the operation went on respiring, thoughimperfectly, and that the respirations soon became more marked andnsphyxial in character, indicating that the blood was not becoming
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Vagus.X. Diaphragm. Fig. 120.—Diagram to show where cuts are made to isolate the chief respiratory center from afferent impulses. properly aerated and that the chemical changes occurring in it wereacting directly on the center, stimulating it to greater activity. Theeonclusion seems warranted that the respiratory center can act auto-matically, for the only possible afferent nerves left in the above prepara-tion were those carried to the center by the fifth nerve (Fig. 120). That the respiratory center is extraordinarily sensitive to changes inthe composition of the blood flowing through it is a fact that has beenknown for a long time, but it is only within recent years that the exact THE CONTROL OF THE RESPIRATION 331 nature of this control and the remarkable sensitivity of the center towardsit have been thoroughly established. We shall return to this importantsubjeel Later. Meanwhile we shall proceed to examine the manner inwhich the center is affected by sensory impulses transmitt

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