Chapter 13. Functional Anatomy of the Gustatory System

13.1 Title slide

Demonstration 13.2
true
true
You must read each slide, and complete any questions on the slide, in sequence.
true
title

Functional Anatomy of the Gustatory System

Interact with depictions of the structures and pathways involved in the perception of taste and flavor.

CLICK ANYWHERE TO BEGIN

Our sense of taste helps us select healthy foods. Things that taste good are usually edible, whereas things that taste bad are often toxic.
Photo: Hisham Ibrahim/Photographer's Choice/Getty Images.

What Is the Functional Anatomy of the Gustatory System?

On average, individual humans have 3,000–12,000 taste buds within small structures called papillae, mostly on the tongue:
  • Fungiform papillae, each containing 3–5 taste buds, are located along the edges and top of the front two-thirds of the tongue.
  • Foliate papillae, small ridgelike folds located on the sides of the tongue near the back, each contain a few hundred taste buds.
  • Circumvallate papillae each contain 200–700 taste buds. The mouth contains only 8–12 of these papillae, all situated in a row at the back of the tongue.

Each taste bud contains 40–100 taste receptor cells (TRCs), elongated neurons with cilia at their outer ends and without axons. Each TRC lives for only a week or so and is then replaced (new TRCs develop from basal cells in the taste bud). The cilia of the TRCs project into a taste pore (an opening onto the surface of the tongue) at the top of the taste bud, where the cilia come into contact with tastant molecules dissolved in saliva.

There are two types of TRCs: receptor cells and presynaptic cells. The membranes of receptor cell cilia contain GPCRs (G-protein coupled receptors) that initiate transduction of sweet, umami, and bitter tastants. Receptor cells do not have synapses with cranial nerve fibers, but presynaptic cells do. In presynaptic cells, receptors take the form of ion channels in the cilia membrane, where transduction of salty and sour tastants is initiated. When tastants are transported through the ion channels, neurotransmitters are released into the synapse and taken up by the nerve fiber, which responds by sending action potentials to the brain.

Receptor cells send signals to the brain by what is termed cell-to-cell signaling: When tastants bind to the receptors on a receptor cell’s cilia, the cell releases ATP into the extracellular fluid within the taste bud. These ATP molecules are taken up by presynaptic cells, which release serotonin into their synapse with cranial nerve fibers. Presumably, differences in the release of ATP and the consequent release of serotonin provide information about the type of tastant transduced by the receptor cell—sweet, umami, or bitter.

Neural signals from taste receptor cells are sent to the brain via cranial nerves VII, IX, and X. These signals travel first to the nucleus of the solitary tract and then through the ventral posterior medial nucleus of the thalamus on their way to the cortex. The first cortical areas to receive taste signals are the anterior insular cortex and the frontal operculum, which constitute the primary taste cortex. Signals then go to the orbitofrontal cortex, the amygdala (where emotion is represented), and the hypothalamus (where hunger is represented).

The orbitofrontal cortex (OFC) appears to play an especially important role in taste and flavor perception. When an animal eats, the responses of neurons in the primary taste cortex aren’t affected by hunger, but neurons in the orbitofrontal cortex respond strongly—indicating high reward value—only when the animal is hungry. This suggests that the primary taste cortex represents taste qualities (sweet, bitter, umami, salty, and sour), whereas the OFC represents the reward value of food.

13.2 Explain - dnd

explain_dnd
You haven't completed the activity on this screen. However, if you leave this screen now, any work you've done on the screen will be saved. Are you sure you want to leave?

Drag and drop each label into the correct blank box on these illustrations of the tongue, papillae, and taste buds.

RESET
Tongue
Taste Bud
Cranial nerve fibers
Circumvallate papilla
Taste pore
Fungform Papilla
Taste bud
Presynaptic cells
Cilia of taste receptor cells
Basal cell
Epithelial cells
Receptor cells
Foliate papilla
Taste receptor cells

13.3 Explain - dnd

explain_dnd
You haven't completed the activity on this screen. However, if you leave this screen now, any work you've done on the screen will be saved. Are you sure you want to leave?

Drag and drop each label into the blank box above the matching description.

RESET
This is an opening onto the surface of the tongue
This develops into a taste receptor cell
These transduce sweet, umami, and bitter tastants
These send taste signals to the brain
These have receptors on them that bind to tastant
These transduce salty and sour tastants
Each taste bud contains 40-100 of these
Taste pore
Cilia of taste receptor cells
Receptor cells
Presynaptic cells
Taste receptor cells
Basal cell
Cranial nerve fibers

13.4 Explain - dnd

explain_dnd
You haven't completed the activity on this screen. However, if you leave this screen now, any work you've done on the screen will be saved. Are you sure you want to leave?

Drag and drop each label into the correct blank box.

RESET

Anterior insular cortex

Hypothalamus

Ventral posterior medial
nucleus of thalamus

Frontal operculum

Nucleus of the
solitary tract

Cranial nerve VII

Orbitofrontal cortex

Cranial nerve IX

Amygdala

Cranial nerve X

13.5 Explain - dnd

explain_dnd
You haven't completed the activity on this screen. However, if you leave this screen now, any work you've done on the screen will be saved. Are you sure you want to leave?

Drag and drop each blue label into the correct blank box in this diagram of the gustatory pathways.

RESET
Taste receptor
cells in taste buds
On anterior
two-thirds of tongue and on soft palate
On posterior
one-third of tongue
On epiglottis and upper esophagus
Representation of reward value of food
Representation
of emotion
Representation
of hunger
Primary
taste cortex
Representation
of taste quality

Anterior insular cortex

Hypothalamus

Ventral posterior medial
nucleus of thalamus

Frontal operculum

Nucleus of the
solitary tract

Cranial nerve VII

Orbitofrontal cortex

Cranial nerve IX

Amygdala

Cranial nerve X

13.6 Explain

explain_text

What Is the Functional Anatomy of the Gustatory System?

On average, individual humans have 3,000–12,000 taste buds within small structures called papillae, mostly on the tongue:

  • Fungiform papillae, each containing 3–5 taste buds, are located along the edges and top of the front two-thirds of the tongue.
  • Foliate papillae, small ridgelike folds located on the sides of the tongue near the back, each contain a few hundred taste buds.
  • Circumvallate papillae each contain 200–700 taste buds. The mouth contains only 8–12 of these papillae, all situated in a row at the back of the tongue.
Each taste bud contains 40–100 taste receptor cells (TRCs), elongated neurons with cilia at their outer ends and without axons. Each TRC lives for only a week or so and is then replaced (new TRCs develop from basal cells in the taste bud). The cilia of the TRCs project into a taste pore (an opening onto the surface of the tongue) at the top of the taste bud, where the cilia come into contact with tastant molecules dissolved in saliva.

There are two types of TRCs: receptor cells and presynaptic cells. The membranes of receptor cell

cilia contain GPCRs (G-protein coupled receptors) that initiate transduction of sweet, umami, and bitter tastants. Receptor cells do not have synapses with cranial nerve fibers, but presynaptic cells do. In presynaptic cells, receptors take the form of ion channels in the cilia membrane, where transduction of salty and sour tastants is initiated. When tastants are transported through the ion channels, neurotransmitters are released into the synapse and taken up by the nerve fiber, which responds by sending action potentials to the brain.

Receptor cells send signals to the brain by what is termed cell-to-cell signaling: When tastants bind to the receptors on a receptor cell’s cilia, the cell releases ATP into the extracellular fluid within the taste bud. These ATP molecules are taken up by presynaptic cells, which release serotonin into their synapse with cranial nerve fibers. Presumably, differences in the release of ATP and the consequent release of serotonin provide information about the type of tastant transduced by the receptor cell—sweet, umami, or bitter.

Neural signals from taste receptor cells are sent to the brain via cranial nerves VII, IX, and X. These signals travel first to the nucleus of the solitary

tract and then through the ventral posterior medial nucleus of the thalamus on their way to the cortex. The first cortical areas to receive taste signals are the anterior insular cortex and the frontal operculum, which constitute the primary taste cortex. Signals then go to the orbitofrontal cortex, the amygdala (where emotion is represented), and the hypothalamus (where hunger is represented).

The orbitofrontal cortex (OFC) appears to play an especially important role in taste and flavor perception. When an animal eats, the responses of neurons in the primary taste cortex aren’t affected by hunger, but neurons in the orbitofrontal cortex respond strongly—indicating high reward value—only when the animal is hungry. This suggests that the primary taste cortex represents taste qualities (sweet, bitter, umami, salty, and sour), whereas the OFC represents the reward value of food.

13.7 Test - dnd

You must complete the question and then click SUBMIT before you can proceed to the next screen.
test_dnd

Question

wfN2f02Mdl0Zhut2ksq2+3CebDOb62p9pU4mHbICu/I=
Slide 7/Test Yourself 1 Matching Activity

Drag each of the blue labels into a blank box in the table, to correctly describe each type of papilla. Then click SUBMIT.

Location Number of taste buds in each papilla
Fungiform papillae
Foliate papillae
Circumvallate papillae

In a row at the back of the tongue

3 - 5

A few hundred

Along the edges and top of the front two-thirds of the tongue

200-700

On the sides of the tongue near the back

13.8 Test - dnd

You must complete the question and then click SUBMIT before you can click proceed to the next screen.
test_dnd

Question

wfN2f02Mdl0Zhut2ksq2+3CebDOb62p9pU4mHbICu/I=
Slide 8/Test Yourself 2 Matching Activity

Drag each of the blue labels into a blank box in the table, to correctly describe each type of taste receptor cell. When you're finished, click SUBMIT.

Types of receptors Tastants transduced Signals sent
to brain via
Receptor cells
Presynaptic cells

Ion channels

Neurotransmitter
release

Cell-to-cell signaling

Salty and sour

GPCRs

Sweet, umami,
and bitter

13.9 Test - dnd

You must complete the question and then click SUBMIT before you can click proceed to the next screen.
test_dnd

Question

/v1YIbiHDNx6O+Cm04kLxRB9Zc9zHsuN4qgPtFMoSQ0=
Slide 9/Test Yourself 3 Matching Activity

Drag each label into the correct blank box, in the order in which these events occur in the process of gustatory transduction and transmission. Then click SUBMIT.

Receptor cells release ATP,
and presynaptic cells release
neurotransmitters

Neural signals are sent to
the brain via cranial
nerves VII, IX, and X

Signals travel to the
amygdala, hypothalamus,
and orbitofrontal cortex

Receptor cells transduce
sweet, umami, and bitter tastants,
and presynaptic cells
transduce salty and sour tastants

Tastants contact the cilia of TRCs
in taste buds on the tongue

Signals travel to the
primary taste cortex

Signals travel via the nucleus
of the solitary tract and the
ventral posterior medial nucleus
of the thalamus

13.10 Activity completed

Activity Complete!
You have completed the activity
Title