Point 9












Pathway of the Gag ReflexThe normal gag reflex is a mass contraction of both sides of the posterior oral and pharyngeal musculature and an indication by the patient of an unpleasant experience. Sensory information (it hurts) comes into the brain stem over C.N.s IX and X (cell bodies in superior ganglia), enters the spinal tract V and terminates in caudal spinal nucleus V. Cells in spinal nucleus V then project bilaterally to nucleus ambiguus (we cannot identify these axons in our sections, but they travel over the TTT). The contractions of the pharyngeal musculature ipsilateral to the stimulus is called the DIRECT response, while the contractions of the musculature contralateral to the stimulus is called the CONSENSUAL response (consensus=agreement). Don't forget that with a lesion of nucleus ambiguus the efferent or motor part of the GAG REFLEX is lost IPSILATERAL to the lesion. Sensory stimulation from the soft palate and pharynx can reach spinal nucleus V (via C.N.s IX and X; superior ganglia), and, via the TTT, both nuclei ambiguui. However, there is contraction of only the muscles innervated by cells in the "alive" nucleus ambiguus. Look at the diagram and contrast the effects of lesions involving (1) C.N.s IX and X, (2) caudal spinal nucleus V and (3) nucleus ambiguus. Also, do the practice questions on the next page. Good luck!