Abstract
Electrophysiological studies demonstrate the existence of chemo- and baroreceptors in the dorsal carotid artery of the tortoise, Testudo hermanni Gmelin. A fine nerve branch, 5–7 μm in diameter, originates from the glossopharyngeal nerve and terminates in the part of the dorsal carotid artery between its origin at the subclavian artery and the bifurcation of the tracheal branch. When afferent impulses were recorded from this fine nerve simultaneously with the blood pressure, two kinds of activity were observed. One, synchronous with blood pressure fluctuation, appears to originate in baroreceptors. The other, non-rhythmic, consisted of an increase of impulse frequency to hypoxia, hypercapnia and NaCN, characteristics of an arterial chemoreceptor. Thus this fine nerve seems to correspond to the mammalian carotid nerve. Afferent innervation of the truncal region including the aorta and the pulmonary artery was nearly the same as that in some turtles.
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