How does taste occur

Such differences are heritable and reflect differences in the number of fungiform papillae and hence taste buds on the tongue. In addition to signal transduction by taste receptor cells, it is also clear that the sense of smell profoundly affects the sensation of taste. Think about how tastes are blunted and sometimes different when your sense of smell is disrupted due to a cold.

The sense of taste is equivalent to excitation of taste receptors, and receptors for a large number of specific chemicals have been identified that contribute to the reception of taste. Despite this complexity, five types of tastes are commonly recognized by humans:. None of these tastes are elicited by a single chemical. Also, there are thresholds for detection of taste that differ among chemicals that taste the same.

For example, sucrose, 1-propyl-2 aminonitrobenzene and lactose all taste sweet to humans, but the sweet taste is elicited by these chemicals at concentrations of roughly 10 mM, 2 uM and 30 mM respectively - a range of potency of roughly 15,fold. Substances sensed as bitter typically have very low thresholds. It should be noted that these tastes are based on human sensations and some comparative physiologists caution that each animal probably lives in its own "taste world".

For animals, it may be more appropriate to discuss tastes as being pleasant, unpleasant or indifferent. Additionally, there are some clear differences among animals in what they can taste.

Cats, for example, do not respond to sweets due to a deletion in the gene that encodes one of the sweet receptors. Perception of taste also appears to be influenced by thermal stimulation of the tongue. In some people, warming the front of the tongue produces a clear sweet sensation, while cooling leads to a salty or sour sensation. A very large number of molecules elicit taste sensations through a rather small number of taste receptors.

Furthermore, it appears that individual taste receptor cells bear receptors for one type of taste. Foods have many different properties that contribute to enjoyment: smell, temperature, and even how they feel in your mouth. One of the most important properties of food is taste, the combination of sweet, sour, salty, bitter, and savory sensations coming from your tongue. How are these signals conveyed from the mouth to the brain? This has long been a mystery. However, scientists looking closely have uncovered remarkable details about the pieces making up the taste system, and how these pieces fit together [ 1 ].

What do we see when we stick out our tongues? Lots of bumps. Most people think they are taste buds, but it is a little more complicated than that Figure 1. The bumps we see are called papillae , and they are a special tough part of our skin. The real taste buds are made up of delicate cells nestled like sections of an orange beneath the surface of the papillae, where they are well protected.

Only the tips of the taste buds poke through to the surface of the tongue. The taste buds cannot be seen with the naked eye, but if you could zoom in, you would see that each of our papillae contains thousands of taste buds, all peeking out [ 2 ]. At their very tips, where they poke out from the tongue, each taste bud cell stores tiny proteins called taste receptors Figure 1 [ 3 ].

The role of taste receptor proteins is to detect substances in your mouth, such as food particles. Taste receptors activate when chewed food mixes with saliva, then flows over and around the papillae like a mushy river.

The receptor proteins ignore most of the mix, but when they detect their target food particles they react, notifying their cells that a taste substance has been detected. This process can be imagined as if the receptors are locks and the food particles are keys. Just as a lock opens only with its matching key, a taste receptor reacts only to its matching type of food particle. When a taste bud cell is notified that a substance such as food has been detected, it goes into action Figure 2.

The taste bud puts dozens of proteins inside the cell to work. These proteins cooperate, rapidly shifting electrically charged atoms called ions here and there, to produce a tiny electrical current inside the cell [ 2 ]. This impulse is so tiny you cannot feel it. However, it is detected by the nerves in your tongue, which are specialists at detecting and passing on electric signals. When the nerves in your tongue receive signals from taste bud cells, they pass them on to more nerves and then more, sending the message racing out the back of your mouth, up through a tiny hole in your skull, and into your brain.

There, your gustatory cortex the taste center of your brain finishes the job of telling you, which taste you perceive, sweet, salty, bitter, sour, or savory. The basic taste system is the same for all of us. Even toddlers pucker their faces at sour lemons, smile when tasting sweet things, and dislike bitterness.

However, people do differ from each other in important ways. All odors that we perceive are molecules in the air we breathe. If a substance does not release molecules into the air from its surface, it has no smell. If a human or other animal does not have a receptor that recognizes a specific molecule, then that molecule has no smell.

Humans have about olfactory receptor subtypes that work in various combinations to allow us to sense about 10, different odors.

Compare that to mice, for example, which have about 1, olfactory receptor types and, therefore, probably sense many more odors. Uniform distribution of taste receptors the myth of the tongue map : Humans detect taste using receptors called taste buds.

Recent evidence suggests that taste receptors are uniformly distributed across the tongue; thus, this traditional tongue map is no longer valid. The senses of smell and taste combine at the back of the throat. When you taste something before you smell it, the smell lingers internally up to the nose causing you to smell it. Both smell and taste use chemoreceptors, which essentially means they are both sensing the chemical environment.

This chemoreception in regards to taste, occurs via the presence of specialized taste receptors within the mouth that are referred to as taste cells and are bundled together to form taste buds.

These taste buds, located in papillae which are found across the tongue, are specific for the five modalities: salt, sweet, sour, bitter and umami. These receptors are activated when their specific stimulus i. In addition to the activation of the taste receptors, there are similar receptors within the nose that coordinates with activation of the taste receptors. When you eat something, you can tell the difference between sweet and bitter. It is the sense of smell that is used to distinguish the difference.

Although humans commonly distinguish taste as one sense and smell as another, they work together to create the perception of flavor. Odorants and tastants produce signal molecules received by receptors, which are then processed by the brain to identify smells and tastes. Odorants odor molecules enter the nose and dissolve in the olfactory epithelium, the mucosa at the back of the nasal cavity.

The olfactory epithelium is a collection of specialized olfactory receptors in the back of the nasal cavity that spans an area about 5 cm 2 in humans. Recall that sensory cells are neurons.

An olfactory receptor, which is a dendrite of a specialized neuron, responds when it binds certain molecules inhaled from the environment by sending impulses directly to the olfactory bulb of the brain.

Humans have about 12 million olfactory receptors distributed among hundreds of different receptor types that respond to different odors. Twelve million seems like a large number of receptors, but compare that to other animals: rabbits have about million, most dogs have about 1 billion, and bloodhounds dogs selectively bred for their sense of smell have about 4 billion.

Human olfactory system : In the human olfactory system, a bipolar olfactory neurons extend from b the olfactory epithelium, where olfactory receptors are located, to the olfactory bulb.

Olfactory neurons are bipolar neurons neurons with two processes from the cell body. Each neuron has a single dendrite buried in the olfactory epithelium; extending from this dendrite are 5 to 20 receptor-laden, hair-like cilia that trap odorant molecules.