File:A text-book of physiology - for medical students and physicians (1916) (14583685729).jpg

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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ex-tensor and flexor muscles of the joints, etc. Physiologists havestudied experimentally the effect upon the heart of stimulatingsimultaneously the inhibitory and the accelerator nerves. Thework- done upon this subject by Hunt seems to make it verycertain that in all such cases the result, so far as the rate isconcerned, is the algebraic sum of the effects of the separatestimulations of the nerve. The inhibitory and the acceleratorfibers must be considered, therefore, as true antagonists, actingin opposite ways upon the heart. The existence of the accel-erator nerves makes possible, of course, their reflex stimulation.Experimentally it is found that stimulation of various sensorynerves—those of the limbs or trunk, for instance—may causereflexly either an increase or decrease in the heart rate, and asa matter of experience we know that our heart rate may beincreased by various changes, particularly by emotional states.The natural explanation of such accelerations is that they are
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Fig. 246.—To show the acceleration and augmentation produced by a strong stimulus.Isolated cats heart, stimulation on left side. The upper curve gives the ventricularcontractions, the lower one the auricular contractions. The lowermost line gives thetime in seconds and the line above indicates the duration of the stimulation of the accel-erator nerve. t due to reflex stimulation of the nerve cells in the central nervoussystem which give rise to the accelerator fibers. But anotherpoint of view is possible. An increase in heart rate may bebrought about either by a reflex stimulation of the accelerator THE CARDIAC NERVES. 595 fibers or by a reflex inhibition of the cardio-inhibitory center.Hunt especially has presented many experimental facts whichindicate that an increase in heart rate from reflex action may beproduced by an inhibition of the tonic activity of the cardio-inhibitory center. He finds, for instance, that when the twovagi are cut stimulation of various sensory nerves fail

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