Gustatory system

In this note, we are going to discuss the anatomy and function of the gustatory system.

Taste, also known as gustation, is a special sense that provides us with information about the foods and liquids we eat and drink.

Gustatory receptors

Taste perception is mediated by gustatory receptors, also known as taste buds, distributed over the tongue surface and adjacent portions of the pharynx and larynx.

Each taste bud contains gustatory epithelial cells that have extensions known as microvilli or taste hairs.

These extensions protrude through a small opening, called the taste pore, into the surrounding fluids.

The dissolved food molecules stimulate these cells, triggering action potentials that are transmitted to the gustatory cortex for interpretation, enabling us to perceive different tastes.

Nerve fibers emerging from the taste bud

To be more specific, there are four types of cells found in taste buds:

Type I gustatory epithelial cells (glial-like): These cells are involved in salt taste perception, although this role is still being debated.
Type II gustatory epithelial cells (receptor): These cells are involved in perceiving bitter, sweet, and umami tastes.
Type III gustatory epithelial cells (presynaptic): These cells are involved in detecting sour tastes.
Type IV gustatory epithelial/basal cells: These cells are located on the basal lamina and are believed to be precursors to types I-III gustatory epithelial cells.

Lingual papillae

The tongue’s surface is covered with numerous epithelial projections called lingual papillae, which house the mentioned taste buds.

There are four types of lingual papillae:

Fungiform papillae, which are located mainly on the apex and anterior part of the dorsum of the tongue.

Vallate papillae, which are arranged in a V-shaped row, situated just in front of the terminal sulcus.

Foliate papillae can be found on either side of the tongue in the form of folds of the mucous membrane.

Filiform papillae, which cover the anterior two-thirds of the dorsum of the tongue. They do not contain taste buds and are not involved in taste perception.

Gustatory pathway

Gustatory information is carried by cranial nerves VII (facial nerve),

IX (glossopharyngeal nerve),

and X (vagus nerve).

The facial nerve’s chorda tympani

supplies the taste buds on the anterior two-thirds of the tongue (specifically the fungiform and foliate papillae).

The area of innervation of the chorda tympani

The gustatory fibers of the greater petrosal nerve, also a branch of the facial nerve, innervate the taste buds located on the soft palate.

The glossopharyngeal nerve provides fibers to the posterior third of the tongue.

The area of innervation of the glossopharyngeal nerve

And the vagus nerve innervates taste buds located on the surface of the palate and epiglottis.

The area of innervation of the vagus nerve

The sensory afferent fibers carried by these cranial nerves synapse in the solitary nucleus of the medulla oblongata.

From there, the information is projected to three different areas:

Through the ventral posteromedial nucleus of the thalamus to the gustatory cortex of the insula.

Here, we become consciously aware of the sensation

Fibers connecting the thalamus with the gustatory cortex

To the lateral hypothalamic area, which is commonly associated with appetite and satiety.

The amygdala, involved in emotion and memory formation

Golosary