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 sustentacular supportive cells. The carotid body contains the most vascularized tissue in the human body . The thyroid gland is very vascular, but not quite as much as the carotid body. The carotid body functions as a sensor: it responds to a stimulus, primarily O partial pressure, which is detected by the type I (glomus) cells, and triggers an action potential through the afferent fibers of the glossopharyngeal nerve, which relays the information to the central nervous system. The carotid body chemoreceptors are primarily sensitive to decreases in the partial pressure of oxygen (P). This is in contrast to the