smell and taste physiology

Question 1

Taste Pathways

Answer 1

1. The sensory nerve fibers from the taste buds on the anterior two thirds of the tongue travel in the chorda tympani branch of the facial nerve, and those from the posterior third of the tongue reach the brainstem via the glossopharyngeal nerve.
2. The fibers from areas other than the tongue reach the brainstem via the vagus nerve.
3. On each side, the myelinated but relatively slowly conducting taste fibers in these three nerves unite in the gustatory portion of the nucleus tractus solitarius in the medulla oblongata.
4. From there, axons of second-order neurons ascend in the ipsilateral medial lemniscus and, in primates, pass directly to the ventral posteromedial nucleus of the thalamus. From the thalamus, the axons of the third-order neurons pass in the thalamic radiation to the face area of the somatosensory cortex in the ipsilateral postcentral gyrus. They also pass to the anterior part of the insula.
5. insular cortex is anterior to the face area of the postcentral gyrus and is the area that mediates conscious perception of taste and taste discrimination.