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How does the tongue recognize different tastes?
Papillae vs Taste Buds
A concept that is critical in understanding taste is the difference between papillae and taste buds. Papillae are the bumps that you can see on the surface of your tongue and are not your taste buds (Source: Neuroscientifically Challenged). Taste buds, however, are located in the walls and crevices of these papillae and are responsible for tasting substances (Source: WhatsUp Dude).
Step 1:
Bits of food particles fall into the crevices of the papillae. These food particles fall into the taste pore of the taste bud, which is considered to be the opening of the taste bud (Source: WhatsUp Dude).
Step 2:
The taste hairs come into contact with fallen food particles that can be tasted, also known as tastants (Source: Neuroscientifically Challenged). These tastants bind to taste receptor cells that are specific to their taste: sour, salty, sweet, savory, and bitter (Source: Frontiers for Your Minds).
Step 3:
To relay specific messages to the brain, these cells must be depolarized or stimulated, causing ions to rapidly shift and release neurotransmitters and ATP, which are chemical substances and molecules used for cellular energy, respectively (Source: Neuroscientifically Challenged). Neurotransmitters and ATP are released depending on the type of cell. Type II cells that detect sweet, savory, and bitter tastes release ATP, while Type III cells that detect sour release neurotransmitters, such as serotonin (Source: Neuroscientifically Challenged). The primary sensory neurons are ignited, creating an impulse (Source: Frontiers for Young Minds). In other words, these sensory neurons are nerve cells that become activated from external stimuli, and they will produce an electrical impulse that will be sent to other areas of the body to communicate a certain message (such as the brain).
Step 4:
The primary sensory neurons run impulses to the cranial nerves located above. The three important cranial nerves involved in tasting are facial, glossopharyngeal, and vagus nerves, which all connect to the taste regions in the brainstem (Source: How Taste and Smell Work). The facial nerve responds to cells in the front ⅔ of the tongue, the glossopharyngeal nerve is the back ⅓ of the tongue, and the vagus nerve is the back of the mouth and part of the esophagus (Source: Neurological Aspects of Taste Disorders).
Step 5:
Once the impulses reach the brainstem, they travel up towards the thalamus, which is responsible for sorting sensory information (Source: Neuroscientifically Challenged). Once the sensory information has been stored, it then can be sent to the gustatory cortex, which is located in the outer portion of the brain called the cerebral cortex. In the gustatory cortex, this is where specific tastes are perceived and interpreted which allows us to experience different tastes (Source: How Taste and Smell Work).
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