CENTRAL NERVOUS SYSTEM CONTROL OF GUSTATION
Taste cells located on the tongue receive innervation from bipolar neurons, which contribute axons to two cranial nerves: the facial (VII) and glossopharyngeal (IX) nerves. The cell bodies of these bipolar neurons reside in the geniculate ganglion of the facial nerve and the distal ganglion of the glossopharyngeal nerve.
Axons from the geniculate ganglion (VII) exit the facial nerve outside the cranium, forming the chorda tympani nerve, which traverses the middle ear cavity. The chorda tympani nerve then merges with the lingual nerve, ultimately innervating taste buds on the anterior two-thirds of the tongue. Meanwhile, central axons originating from the distal ganglion (IX) travel to the tongue via the lingual nerve, entering the base of the tongue and providing sensory fibers to taste buds in the posterior portion.The central processes of bipolar neurons from the geniculate and distal ganglia extend into the nucleus of the solitary tract in the medulla oblongata. Figure 13.2 explains efferent fibers originating from the nucleus of the solitary tract ascend as the solitario-thalamic tract, terminating in the ventral posteromedial nucleus of the thalamus.
Thalamic neurons then project to the ipsilateral cerebral cortex, facilitating the perception of taste. Additionally, the nucleus of the solitary tract projects to the amygdala within the limbic system, linking taste perception with emotional and behavioral responses. This neural pathway highlights the complex connectivity between taste receptors on the tongue, cranial nerves, brainstem nuclei, thalamus, and cerebral cortex, as well as their integration with regions associated with emotional processing (Figure 13.2).