CQC 3.02 How we Taste — The Labelled Lines Model

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1: fungiform papillae, 2: taste buds.

The ridges on our tongues are not taste buds, but papillae. There are three types of papillae: fungiform, mainly positioned at the front of the tongue; foliate, found around the sides; and circumvallate, which are larger and mainly located at the back of the tongue. 

Taste buds are protected in tissue surrounding the sides of the papillae and open up to the mouth through a small pore. Each bud is made up of 50–150 taste receptor cells, and each of these extends into the pore with a small hair attached to each cell. This is similar to the way in which the the cilia extend from the olfactory sensory neurons in the olfactory epithelium in our noses. 

You may remember that the olfactory bulb works as a kind of prefilter for aromas. There is no equivalent of the olfactory bulb when it comes to tasting. Every taste receptor cell on every taste bud is connected, in an unbroken link, all the way to the gustatory cortex in the brain. Every taste bud has cells to detect each of the five tastes: Bitter, Sour, Salty, Sweet, Umami. Each individual taste receptor cell is hardwired all the way to the brain via axons that travel through one of three separate nerve pathways: the facial nerve, the glossopharyngeal nerve, and the vagus nerve. This system is known as the Labelled Lines Model.

1: vague nerve, 2: glossopharyngeal nerve, 3: facial nerve, 4: pathway to brain through brainstem.

1: gustatory cells, 2: basal cells, 3: gustatory hair, 4: taste pore, 5: taste receptor (epithelial cells).

Taste buds are made up of epithelial cells of two different types. The gustatory cells identify and react with chemicals that have dissolved into our saliva. The basal cells are stem cells that grow into new gustatory cells as they reproduce themselves, approximately every week.

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