Glossopharyngeal branch

The carotid bodies have been known since 1743. They are small, pinkish neurovascular structures 1-2 mm in diameter they are located at the posterior aspect of the common carotid, where it divides into the internal and external carotids. Carotid bodies are vascularized by the occipital branch of the external carotid. The efferent nerve fibers of the carotid body converge into the carotid branch of the ninth cranial nerve, or glossopharyngeal nerve. 

Histologically, three structures can be distinguished in the carotid bodies epithelioid cells, vascular sinuses, and nerve endings. The epithelioid cells are assembled in cords in close contact with the vascular sinuses and with nerve endings. This rich innervation of the epithelioid cells is derived from branches of the carotid sinus nerves, which arise from the glossopharyngeal trunk. The carotid body is activated by severe anoxemia, hypercapnia, and lowered pH. 

Figure 8 Integrated antidromic neural activity in the carotid sinus nerve (CSN) and lingual nerve (LN) branches of the glossopharyngeal nerve (IXth n.). Nerve preparation was superfused in vitro. Superimposed traces show that application of a 100-pg bolus (arrows) of ACh to the petrosal ganglion evokes a substantial increase in the CSN and LN nerve discharge, which is inhibited in the presence of 100 pM mecamylamine, a nicotinic receptor antagonist.

Housley GD, Martin-Body RL, Dawson NJ, Sinclair JD. Brain stem projections of the glossopharyngeal nerve and its carotid sinus nerve branch in the rat. Neiuoscience 1987 22 237-250. 

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