File:A text-book of human physiology (1906) (14790382273).jpg

Identifier: textbookofhumanp00tige (find matches)
Title: A text-book of human physiology
Year: 1906 (1900s)
Authors: Tigerstedt, Robert, 1853-1923 Murlin, John R. (John Raymond), b. 1874, tr
Subjects: Physiology
Publisher: New York and London, D. Appleton and Co.
Contributing Library: Columbia University Libraries
Digitizing Sponsor: Open Knowledge Commons

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and so supplying them with nourishment (Fritsch). When the blood supply to the brain is considerably reduced by compressionof the carotids on both sides, unconsciousness results, in many cases at least,because the nerve cells are functionally incapacitated. FUNCTIONS OF THE NERVE CELL 573 Stensons experiment of clamping the abdominal aorta teaches us also thatthe nerve cells in the spinal cord very soon suffer from the lack of blood.The posterior extremities become paralyzed soon after the aorta is closed off,not because of the absence of blood in those parts but because of its absencefrom the spinal cord. Fredericq has investigated these phenomena more closely and has reachedthe following conclusions for the dog: Some fifteen to twenty seconds after theclamp is applied a temporary excitation of the motor cells begins, but withinthirty to forty seconds the motor paralysis is complete. Up to this time thesensibility of the posterior parts is entirely unaffected; but after one and one-
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Period ofExcitation;Convulsions Period of Respiratory Pause FinalGaspings All Respirations Stopped Fig. 257.—The relative resistance of several nerve centers in asphyxiation, schema, after Lander-gren. , the vasomotor center in the medulla; . .1 , the cardiac inhibitory center; -, the respiratory center; -• ■, the vasomotor center in the spinal cord. half minutes a hyperaesthesia sets in, followed by anaesthesia, which is completeat the end of three minutes. If now the clamp is removed, sensibility returns infive to ten minutes, but motility somewhat later. By continuing the occlusionlong enough the paralysis and anaesthesia become permanent. From these facts we reach the very ini))ortant conclusion that differentnerve cells have very different powers of resistance to anaemia. Other observations go to show that the endurance of different nerve cellsunder acute asphyxiation is very different. The schema in Fig. 257 repre-sents, according to Landergren, the relative excitability a

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