Gustation in animals
Gustation in animals is the process of detecting dissolved chemicals emitted from the ingested food. It is the sense of taste.
This is carried out by receptor known as taste buds. There are almost 15,000 taste buds in the porcine oral cavity and throat, while 1 550 in the lizards, but only 24 in chickens.
The taste buds are not able to discriminate between different molecules as olfactory system.
Taste buds are onion shaped structure that contains numerous taste receptor cells. It has a pore that opens onto the surface where the tastants (chemicals from the food) enter and contact the receptors.
On its apical surface, the taste bud has number of microvilli, which also contain receptors and ions channels to mediate taste signal.
Gustatory pathway
Taste impulses from the anterior two third of the tongue pass through chorda tympani branch of the facial nerve‚ thence to nuclei tractus solitarius of the brain stem, while the posterior one-third sends the taste sensations through the glossopharyngeal nerve to nuclei tractus solitarius. Vagus receives the sensory inputs from the base of the tongue and other parts of the pharyngeal region.
Thalamic area adjacent to ventrobasal complex receives the second order neurons from the nuclei tractus solitarius. The third order neurons originate from the thalamus to the lower tip of the post central gyrus in the parietal cortex, the gustatory cortex. Some of the third order neurons also project to the nearby opercular – insular area‚ located deep in the sylvian fissure.
Taste reflex
Tractus solitarius transmits impulses to the superior‚ and the inferior salivatory nuclei‚ thus reflexly regulates the secretions of the submandibular, sublingual and the parotid glands.