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Identifier: textbookofphysio1916howe (find matches)
Title: A text-book of physiology : for medical students and physicians
Year: 1916 (1910s)
Authors: Howell, William H. (William Henry), 1860-1945
Subjects: Physiology Medicine
Publisher: Philadelphia and London : W. B. Saunders Company
Contributing Library: Yale University, Cushing/Whitney Medical Library
Digitizing Sponsor: Open Knowledge Commons and Yale University, Cushing/Whitney Medical Library

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the im-portant role of a vasoconstrictorcenter has not been determinedhistologically. The region has,however, been delimited roughlyby physiological experiments. Ifthe brain is cut through at thelevel of the midbrain there is nomarked loss of vascular tone inthe body at large. If, however,similar sections are made fartherand farther back a point isreached at which vascular paralysis begins to be apparent and apoint farther down at which this paralysis is as complete as itwould be if the cervical cord were cut. Between these two pointsthe vasoconstrictor center must lie. The careful experiments ofthis kind made by Dittmar* are now somewhat old. Accordingto his description, the center is bilateral,—that is, consists of agroup of cells on each side,—and lies about the middle of the fourthventricle in the tegmental region, in the neighborhood of the nucleusof the facial and of the superior olivary. In the rabbit it has a* Berichte d. Sachs. Akademie, Math.-phys. Klasse, 1873, p. 449.
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Fig. 253.—Schema to show the pathof the vasoconstrictor fibers from the vaso-constrictor center to the blood-vessels andthe mechanism for the reflex stimulationof these fibers : v. c, The vasoconstrictorcenter; 1, the central neuron of the vaso-constrictor path; 2, the spinal neuron(preganglionic fiber); 3, the sympatheticneuron (postganglionic fiber); a, the arte-riole ; 4, the sensory fibers of the posteriorroot making connections by collateralswith the vasoconstrictor center; 5, an in-tercentral fiber (efferent) acting upon thevasoconstrictor center. THE VASOMOTOR NERVES. 611 length of 3 mms., a breadth of 1 to 1.5 mms., and lies about 2to 2.5 mms. lateral to the mid-line. Assuming the existence ofthis group of cells, we must attribute to them functions of the firstimportance. Like other motor cells, they are capable of beingstimulated reflexly and by this means the regulation of the blood-flow is largely controlled. Moreover, they are in constant activity,•—due doubtless als

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