There are two chemical senses: taste (gustation) and smell (olfaction). They are chemical senses since the stimuli are the molecules of the object you are tasting or smelling.
Every sense has its purpose, and these two serve as warning signs. For example, if you smell food that's old or rotten, you won't eat it, therefore saving your body from later pain. If you are in your house and you smell smoke, your senses would be heightened and you would escape immediately. Chemical senses help us survive in any environment.
We have five main taste receptors: sweet, sour, salty, bitter, and umami. Umami is often described as "savory" or "meaty"—the kind of taste we experience when we eat things like broth, gravies, soups, and soy sauce.
When you eat something, your taste buds catch the chemicals of the food. Taste buds are the most concentrated on your tongue, but there are also some on the roof of your mouth. Something really interesting is that you can only taste food that dissolves with your saliva.
Babies 👶🏼 show a preference for sweet 🍭 and salty 🥨 foods and avoid bitter and sour foods. We often all have a preference for sweet and salty, and they allow us to survive, whereas if a baby tastes something bitter or sour, they would think poison or rotten.
Remember: expectations influence perception. Therefore, your expectations of how food tastes could change what you think of it when you really try it.
Also, taste is very subjective and can change based on culture and emotion as well. Generally, you should be aware that pleasurable tastes attracted our ancestors to rich, good-tasting foods that enabled our survival.
Our sense of smell also enabled our survival. We only smell something when molecules of that substance reach a cluster of our receptor cells in our nose. Isn’t that wild? Everything that you smell actually touches your nose!
These receptor cells respond to a familiar sense and instantly alert the brain. For example, mothers and infants form a chemistry relationship because of their sense of smell. Infants always know exactly who their mother is just by the familiar scent.
Remember the trichromatic theory? We only have three color, receptors but when multiple are activated, we see infinite colors 🌈 This happens with smell as well. Certain molecules excite certain receptors and a mix could create new smells.
As people age, we lose our sensitivity to taste and smell. This is why you may see an older person overusing spices.
—This is the only sense that doesn't go through the thalamus.
If you recall, whatever you see goes from your eyes, to the optic nerve, to the thalamus, and then finally to the visual cortex. The same goes for every other sense, besides smell.
Image Courtesy of Coffee Association.