07. Gustation

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The tongue is a musculo-membranous body is 17 muscles [ 116 ] powerful innervated by the hypoglossal nerve [ 107 ]. It plays a fundamental role in language and food. The language also plays the role of a principal chemical sense [sensory receptor 36 ]: The tasting [ 38 , 72 ].

1. Reception:

Found on the lingual mucosa many projections called (the lingual papillae) [ 99 ]. We distinguish: Goblet buds [ 4 , 72 ], fungiform [ 41 ] and thread [ 72 ]. These are the goblet and fungiform papillae which are the structures responsible for gustation [ 99 ].

Unlike compounds that are free nerve endings neurosensory cells rudimentary olfactory receptors, taste transduction is at specialized receptors (taste buds) [ 41 ]. These buds are at the level of the mucous membranes and fungiform papillae of [ 99 ], they are formed of support cells (basal cells) that surround the receiving cells arranged concentric.

Each bud contains 50 to 150 recipient cells [ 38 ]. Each receptor cell contains a ciliated apical responsible for capturing and chemicals basal pole hinged to a sensory neuron.

We distinguish four basic flavors: The sweet, the bitter, acid and salt [ 1 ]. There are other flavors that add to this list: astringent flavor (cranberries, tea, tannins), pungent (chilli, ginger), metallic taste (Ferrous sulfate hydrate), oily flavor, flavor starch ...

Requires that chemicals are soluble in saliva to be detected by taste cells.

It is commonly said that there are specific areas in the language for each flavor, which is not true. In fact, these flavors can be detected by the entire surface of the stock [ 41 ].

Once bound to the cell membrane, the chemicals will activate a cascade of biochemical reactions that ultimately will depolarize the cell receptor [ 41 ].

2. Transmission [ 5 ]:

Once depolarized, The Secret gustatory cell neurotransmitters that act on the sensory neuron affiliate and generate an action potential that will spread throughout the nerve fiber to the brain stem.

Taste buds the previous two thirds of the tongue are innervated by the facial nerve [ 3 ]. Although the trigeminal nerve by its lingual branch also innervates this part, its action is limited to the somatosensory sensitivity. The glossopharyngeal nerve provides tasting and somesthesia the posterior third of the tongue [ 3 ].

The cell bodies of these nerve fibers are located in the geniculate ganglion (VII) [ 116 ] and the upper petrosal ganglion (IX). The postganglionic fibers enter the brain stem and ending in the corresponding rings where they make relay with other neurons that join the posterior and ventral parts of the thalamus.

At this level, these neurons are relay with fibers that follow the internal capsule to terminate in the primary gustatory cortex [ 5 ] at the near post parietal gyrus lobe.

3. Perception:

Primary gustatory cortex will leave fibers that project to the secondary gustatory cortex [ 5 ] in the temporal lobe, but also in the hypothalamus, amygdala and insula, which gives an emotional component to taste.

Finally, it should be noted that the nerve fibers of the tasting does not cross the midline, so that the gustatory cortex receives and analyzes left primary gustatory information from the left side of the tongue and vice versa [ 38 ].