A text-book of physiology for medical students and physicians . d, in the latter case it would be quickened if the center werepreviously in a state of activity. The Tonic Activity of the Cardio-inhibitory Center.—Thecells of the cardio-inhibitory center are in constant activity to agreater or less extent. As a consequence, the heart beat is kept con-tinually at a slower rate than it would normally assume if theinhibitory apparatus did not exist. This tonic activity of the vagusis beautifully exhibited by simple section of the two vagi, or by inter-rupting, in some other way—cooling, for exampl
A text-book of physiology for medical students and physicians . d, in the latter case it would be quickened if the center werepreviously in a state of activity. The Tonic Activity of the Cardio-inhibitory Center.—Thecells of the cardio-inhibitory center are in constant activity to agreater or less extent. As a consequence, the heart beat is kept con-tinually at a slower rate than it would normally assume if theinhibitory apparatus did not exist. This tonic activity of the vagusis beautifully exhibited by simple section of the two vagi, or by inter-rupting, in some other way—cooling, for example—the connectionbetween the center and the heart. When the two vagi are cut theheart rate increases greatly and the blood-pressure rises on accountof the greater output of blood in a unit of time (Fig. 242). Section 580 CIRCULATION OF BLOOD AND LYMPH. of one vagus gives usually a partial effect,—that is, the heart-rateis increased somewhat,—but it is still further increased by sectionof the second vagus. The exact result obtained when the nerves are. Fig 242 —To show the effect of section of the two vagi in the dog upon the rate ofheart beat and the blood-pressure: 1 marks the section of the vagus on the right side;2 section of the second vagus. The numerals on the vertical mark the blood-pressures ;the numerals on the blood-pressure record give the rate of heart beats. (Dawson.) severed separately varies undoubtedly with the conditions.—forinstance, with the intensity of the tonic activity of the life, speaking in general terms, the cardio-inhibitorycenter keeps the brakes on the heart rate, and the extent of itsaction varies under different conditions. When its tonic action isincreased the rate becomes slower; when it is decreased the ratebecomes faster. In all probability, this tonic action of the center,like that of the motor centers generally, is in reality a reflex is, it is not due to automatic processes generated within thenerv
Size: 2141px × 1167px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookautho, bookcentury1900, bookdecade1910, booksubjectphysiology
