Carotid sheath sternum. The four major structures contained in the carotid sheath are: The carotid artery lies medial to the internal jugular vein, and the vagus nerve is situated posteriorly between the two vessels. In the upper part, the carotid sheath also contains the glossopharyngeal nerve (IX), the accessory nerve (XI), and the hypoglossal nerve (XII), which pierce the fascia of the carotid sheath. The ansa cervicalis is embedded in the anterior wall of sheath. It is formed by "descendens hypoglossi" (C1) and "descendens cervicalis" (C2-C3). The three major fascial layers in the neck contribute to the carotid sheath: the investing fascia,
Carotid body Carotid body The carotid body ("carotid glomus" or "glomus caroticum") is a small cluster of chemoreceptors and supporting cells located near the fork (bifurcation) of the carotid artery (which runs along both sides of the throat). The carotid body detects changes in the composition of arterial blood flowing through it, mainly the partial pressure of arterial oxygen, but also of carbon dioxide. Furthermore, it is also sensitive to changes in pH and temperature. The carotid body is made up of two types of cells, called glomus cells: glomus type I cells are peripheral chemoreceptors, and glomus type II cells are