Chapter 17 - Taste

5 primary tastes:

  1. Sour - H+ release from acids

  2. Sweet - sugars and artificial sweeteners

  3. Bitter - Variety of foods such as caffeine

  4. Umami - amino acids present in food such as glutamate (meaty & savory)

  5. Salty - Na+ in food


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

Each taste bud contains 3 kinds of epithelial cells:

  1. supporting cells

  2. gustatory receptor cells

  3. basal stem cells


Functions of taste bud cell:

  1. supporting cells - surround GRC (gustatory receptor cells) in each taste bud

  2. GRC - contain gustatory microvilli that project from each GRC to the external surface through the opening in the taste bud called the taste pore

  3. basal cells - found at the periphery near the connective tissue layer


Where are the taste buds found? - on elevations on the tongue called papillae

What is the purpose of papillae? - increase surface area and provide a rough texture to the upper surface of the tongue


3 types of taste buds:

  1. vallate papillae - back of the tongue inverted V shape row

  2. fungiform papillae - mushroom shaped elevations scattered over entire surface

  3. filiform papillae - tactile receptors but no taste buds to increase friction between the tongue and food



What is the transduction of gustation?

  1. chemicals that stimulate GRC = tastants

  2. tastants dissolves in saliva and makes contact with the GRC microvilli which are the sites of taste transduction

  3. sensory neurons synapse with GRC

  4. the receptor potential arises differently for different tastants

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


Transduction varies by tastant:

  1. Salty

    1. Na+ entry into the Na+ channels of the gustatory receptor cell

    2. Depolarization

    3. Neurotransmitter release

    4. 1st order neurons

  2. Sour

    1. H+ entry into the H+ channels of the gustatory receptor cell

    2. Depolarization

    3. Neurotransmitter release

    4. 1st order neurons

  3. Sweet, bitter, umami

    1. Bind to receptor proteins (does not enter)

    2. G protein activation

    3. IP3 acts 2nd messenger

    4. Depolarization

    5. Neurotransmitter release

    6. 1st order neurons


Gustatory Pathway

  1. 3 cranial nerves contain axons that innervate the taste buds

    1. facial nerve (VII)

    2. glossopharyngeal nerve (IX)

    3. vagus nerve (X)

  2. Nerve impulses travel from taste buds to cranial nerves to gustatory nucleus in the medulla oblongata

  3. From the medulla, some axons project to the limbic system and hypothalamus, others to the thalamus. Taste signals projecting from the thalamus to the gustatory cortex of the cerebrum give rise to conscious perception of taste and discrimination of taste sensations