Final answer:
The glossopharyngeal nerve is the ninth cranial nerve originating in the medulla oblongata within the hindbrain, exiting through the jugular foramen. It performs sensory and motor functions, including taste sensation, triggering saliva production, and mediating the gag reflex. It is tested by assessing the response to taste stimuli and gag reflex elicitation.
Step-by-step explanation:
The glossopharyngeal nerve, also known as the ninth cranial nerve, originates in the medulla oblongata, which is part of the hindbrain. This brain region develops from the rhombencephalon and includes the medulla oblongata, pons, and cerebellum. The nerve exits the skull through the jugular foramen and extends down to the pharynx and tongue.
The glossopharyngeal nerve is both sensory and motor in type. It is responsible for the contraction of muscles in the tongue, part of the sense of taste, and initiating salivation. This nerve carries taste sensations from the posterior third of the tongue and general sensory information from the pharyngeal walls, which can trigger the gag reflex. Its motor functions include stimulating the swallowing reflex and contributing to the autonomous control of the parotid salivary glands.
In testing of nerve function, the application of various taste stimuli on the tongue and the elicitation of the gag reflex are used to assess the integrity of the glossopharyngeal nerve. Additionally, the nerve works in conjunction with the facial nerve to coordinate the act of salivation through visceral reflex arcs and their associated salivary nuclei and parasympathetic fibers.