Common carotid artery the common carotid artery ascends in the neck without any subdivision, either the external or the internal carotid being absent; and in a few cases the common carotid has itself been found to be absent, the external and internal carotids arising directly from the arch of the aorta. This peculiarity existed on both sides in some instances, on one side in others. The common carotid usually gives off no branch previous to its bifurcation, but it occasionally gives origin to the superior thyroid artery or its laryngeal branch, the ascending pharyngeal artery, the inferior thyroid artery, or, more rarely, the
Carotid body central chemoreceptors in the medulla oblongata that are primarily sensitive to changes in pH and P (a decrease in pH and an increase in P). The carotid body chemoreceptors are also sensitive to pH and P, but only secondarily. More specifically, the sensitivity of carotid body chemoreceptors to decreased P is greater when pH is decreased and P is increased. The output of the carotid bodies is low at an oxygen partial pressure above about 100mmHg (13,3 kPa) (at normal physiological pH), but below 60mmHg the activity of the type I (glomus) cells increases rapidly due to a decrease in