(From Dr. Glasser’s Lecture, 11 July 2000, by Brian Buschman)
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Taste is sweet sour, bitter and salty. The tastes are actually sensed with sweet on the tip, sour on the edges, salty on the anterior edges and bitter posteriorly. Bitter is the most potent of our tastes to allow us to notice poisons easily since most poison is bitter.
Don’t get taste and flavor confused as flavor is a function of olfaction when food particles go up the back door into the nasopharynx.
Taste receptors are epithelial cells with a turnover rate of every week or two. This can only happen since they are epithelial cells and not nerve fibers.
Taste receptors respond to multiple taste qualities. Most of them sense two or three different tastes but we recognize specific tastes based on combinations of firing.
Taste buds are innervated by CN’s VII, IX and X and the chief sensory part of V. Fibers from all of them enter the nucleus of the tractus solitarius (NTS) ipsilaterally.
They follow the solitary tract ipsilaterally up to the VPM (the thalamic nucli that takes care of sensation from the head). More specifically it goes to the parvicellular VPM (VPMPC). The VPMPC sends fibers to the primary gustatory cortex. In the precentral gyrus is the insula or fronto-parietal operculum which is the primary gustatory cortex. The primary gustatory cortex also has some projections to the amydgala to access the limbic system.
The NTS can also go out to the ventricular formation to the solitary tract or to the dorsal motor nucleus of the vagus.
The gag reflex uses input from the NTS to the spinal nucleus of V to the ambiguus o X and the hypoglossal nucli bilaterally. This causes bilateral swallowing even if only one side is stimulated.
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