Chapter 17 Taste


Taste is a chemical sense, but is much simpler than olfaction

There are 5 primary tastes…

-Sour (H+ release from acids)

-Sweet (Sugars and artificial sweeteners)

-Bitter ( Variety of foods like caffeine)

Salty ( Na+ in food)

Umami (Amino acids present in foods such as gluatamate)

Taste buds- oval bodies contain receptors for the sensation of taste

Each taste bud contain 3 kinds of epitheal cells

-Supporting cells (Surrounding gustatatory receptor cells in each taste bud)

-Gustatory receptor cells (Contain gustatory microvilli (Hairs) that project from each GRC to the external surface through the opening in the taste bus called the taste pore)

-Basal stem cells (Found at the periphary near the connective tissue layer)

-GRC have a lifespan of 10 days

Taste buds are found on elevations on the tongue called papillae

Pappillae (increases surface area and provide a rough texture to the upper

surface of the tongue

3 types of taste buds..

-Vallate papillae (Back of the tongue inverted V shaped row)

-Foliate papillae (Located on lateral margins on the tongue, early childhood

-Fungiform Papillae (mushroom shaped elevations scattered over entire surface

Filiform papillae (Tactile receptors but no taste buds to increase friction between the tongue and food)

-Tastants (Chemicals that stimulate GRC)

Tastants dissolve in saliva and makes contact with the GRC microvilli which are the site of taste transduction

First-order sensory neurons synapse with GRC

The receptor potential arises differently for different tastants

GRC responds to only one type of tastant

Taste buds contain GRC for each type of tastant, allowing all of the primary tastes to be detected in all parts of the tongue

Different tastes arise from activation of different combinations of GRC’s and how the brain interprets the combination

(Salty)

Salty tastant

  1. Na+ entry into Na+ channels of GRC

  2. Depolarazation

  3. Neurotransmitter release

  4. 1st order neurons


(Sour)

sour tastant

  1. H+ entry into H+ channels of the GRC

  2. Depolarazation

  3. Neurotransmitter release

  4. 1st order neurons


(Sweet, bitter, umami)

  1. Bind to recepter proteins (Does not enter)

  2. G protein activation

  3. IP3 acts 2nd messenger

  4. Depolarazation

  5. Neurotransmitter release

  6. 1st order neurons


The Gustatory pathway (the route taken by the gustatory info from the Gustatory epitheal cells to the brain were concious awareness of taste occurs)

Step 1: 3 cranial nerves contain axons that innervate with taste buds

Facial nerve VII- taste buds in the anterior 2/3 of tongue

Glossopharyngeal IX nerve- taste buds posterior 1/3 of tongue

Vaugus X nerve- taste buds in throat and epiglottis

Step 2: Nerve impulses travel from taste buds to cranial nerve to gustatory nucleus in the medulla oblongata

Step 3: From the medulla, some axons project to limbic system and hypothalmus, others to thalmus. taste signals projecting from the thalmus to the gustatory cortex of cerebrum give rise to conscious perception of taste and discrimination tase perceptions.