Gustatory System

Gustatory System Definition in Psychology

Did you know that taste--as basic as it may sound--helped our ancestors survive? Gustation, or the sense of taste, aided them in their search for food as an energy source while avoiding possibly harmful substances. Furthermore, the sense of taste is a mix of the olfactory (smell) and gustatory (taste) senses.

Woman eating, pexels.com

More importantly, what sensory system is responsible for our taste? It’s the gustatory system!

Gustatory System: Anatomy

The organs of the gustatory system include our tongue, papillae, and taste buds. First, let’s look at our primary taste organ, the tongue.

Tongue

Tongue papillae, commons.wikimedia.org

The tongue contains small bumps called papillae. These bumps create a rough surface on the tongue that helps keep food in the mouth. We have four types of papillae: fungiform, circumvallate, foliate, and filiform.

Fungiform papillae: Our tongue contains 200–400 fungiform papillae with 3-5 taste buds each, most of which are at the tip and edges.

Circumvallate papillae: Around 7–12 circumvallate papillae form a V-shape at the base of the tongue, containing a hundred taste buds.

Foliate papillae: We have about 20 foliate papillae that look like folds on the tongue’s sides with a hundred taste buds each.

Filiform papillae: Most of the papillae on the tongue are filiform papillae, which sense temperature, pain, and texture.

Taste buds

Schematic drawing of foliate papillae with the brown circles on the walls of the papillae representing taste buds, commons.wikimedia.org

Inside the papillae are the taste buds, containing 10–50 gustatory or sensory cells, each forming a bud.

A closer look at a taste bud, commons.wikimedia.org

Taste cells are sensitive to these four basic tastes: sweet, salty, sour, and bitter. Let’s look at some examples of chemical stimuli in food:

• The salty taste you like from your favorite chip or pizza is the dissolved salt crystals (sodium hydrochloride) in your saliva.
• The sour taste is from acids in food and beverages, such as citric acid in lemonade.
• The sweet taste perception is a result of the presence of glucose and other sweet substances (e.g., fructose found in fruits or artificial sweeteners).
• The bitter taste comes from the bitter compounds present in food and medicine, such as alkaloids (e.g., wine, beer, and aspirin).

Taste hairs (called microvilli) on the gustatory cells pick up food molecules from the taste pore in the taste buds. Some gustatory cells are more sensitive to sweet tastes, while others respond more to salty, sour, savory, or bitter flavors. There are also nerve fibers connected to these cells.

Our tongue contains many taste buds. But, there are also taste cells throughout the oral cavity, such as the throat and esophagus. Adults have about 2,000 to 4,000 taste buds.

What happens if you burn your tongue? If you burn your tongue, you may lose some taste buds, but the good news is that they can grow back quickly. A taste bud usually lasts between 10 and 14 days.

Gustatory Sensory System

Just like our olfactory sense, our sense of taste is a chemical sense. To taste something, we rely on sensory receptors that respond to molecules in the food we eat. Furthermore, our brains have connections to our gustatory sensory system, which ultimately tells us whether we accept or reject particular food. Since smell, touch, and temperature can change how something tastes, they can also change the quality of the food stimuli and how it tastes.

Eating chocolate, pexels.com

Try eating your favorite candy or chocolate while you hold your nose. Observe how the taste changes when you release your nose. You’ll notice that the food’s aroma impacts its flavor. A food’s flavor is a combination of both its olfactory and gustatory qualities.

So, when we eat something, how does the gustatory system work?

Suppose you ate a piece of candy. Sugar molecules (chemical stimuli) dissolve in the saliva and bind to taste receptors on our tongue, mouth, and throat, causing chemical changes within the receptors. Depending on the location of the receptor, neurotransmitters (chemical messengers) are released by taste receptors due to these chemical changes, activating neurons that send the sweet flavor message to the brain. A corresponding cell in the brain receives the message from the receptor.

Gustatory System: Cranial Nerves

Cranial nerves, commons.wikimedia.org

Besides the gustatory sensory system, cranial nerves also help us experience taste. So, what are cranial nerves?

Taste molecules (tastants) activate gustatory cells, causing neurotransmitters to be released, which then activate sensory neurons (nerve cells) in the cranial nerves.

The cranial nerves involved with taste information include the facial, glossopharyngeal, and vagus cranial nerves.

• The facial nerve (VII) involves our sense of taste.
• The glossopharyngeal nerve (IX) affects the taste and swallowing.
• The vagus nerve (X) impacts heart rate and digestion.

Each cranial nerve corresponds to a group of taste buds in a specific tongue region.

• The facial nerve (VII) corresponds to taste buds in the tongue’s anterior (front) part.
• The glossopharyngeal nerve (IX) corresponds to taste buds in the tongue’s posterior (back) part.
• The vagus nerve (X) corresponds to the taste buds in the very back area of the tongue.

The cranial nerves transmit taste information to the brain’s various regions.

Gustatory System: Pathway

The gustatory system does a lot of work behind the scenes when you eat your favorite food. Let’s look at the process of producing taste.

Our taste buds send nerve impulses to the gustatory nucleus in the medulla oblongata through the facial, glossopharyngeal, and vagus nerves. The brain’s lowest portion is the medulla oblongata. This region is a vital pathway for nerve signals traveling to and from the body.

Inside the gustatory nucleus are neurons that store information about taste. Neurons then terminate their signals in the gustatory nucleus, and the new information passes now to the thalamus. All movement and sensory information—aside from smell—passes through the thalamus, found in the brain’s center, before being relayed to the cerebral cortex and limbic system.

From the thalamus, the information goes to the gustatory cortex, located in the cerebral cortex (outermost brain surface).

The limbic system, composed of the hippocampus, hypothalamus, and amygdala, involves our emotional states and memories. This part of the brain tells us whether the taste we receive is pleasant.