3.6 Chemical Senses

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. 

Gustation 👅

** 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. Your taste buds are embedded in a tissue called fungiform papillae, which are the little bumps on your tongue. Taste is one of those senses that differ greatly from person to person. If you have more taste buds, the more chemicals are absorbed so you taste the food more intensely. 

** Fun fact: What we think as flavor is actually a combination of taste and smell!**

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.

Olfaction 👃

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!

The receptor cells then send information to the olfactory bulb, which gathers more information and sends it to the brain. This message goes directly to the amygdala (for emotional impulses) and then to the hippocampus (memory). 

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. This direct connection to the brain is the reason why smell is such a powerful trigger for memories!

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.

**Fun Fact—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. **

This becomes very interesting and explains why certain smells may remind you of a person or place. Your sense of smell goes directly to the brain and there is an immediate response of these receptors and molecules.

Image Courtesy of Coffee Association.

Practice MCQs

Now let's dig into a little practice, shall we??

1. Sell and taste are called _______ because _______.

   A. energy senses; they send impulses to the brain in the form of electric energy.

   B. chemical senses; they detect chemicals in what we taste and smell.

   C. flavor senses; smell and taste combine to create flavor.

   D. chemical senses; they send impulses to the brain in the form of chemicals.

   E. memory senses; they both have powerful connections to memory.

2. Our sense of smell may be a powerful trigger for memories because

   A. we are conditioned from birth to make strong connections between smells and events.

   B. the nerve connecting the olfactory bulb sends impulses directly to the limbic system.

   C. the receptors at the top of each nostril connect with the cortex.

   D. smell is a powerful cue for encoding memories into long-term memory.

   E. strong smells encourage us to process events deeply so they will most likely be remembered. 

✨✨

✨✨

✨✨

✨✨

✨✨

✨✨

✨✨

✨✨

Answer:

1. Sell and taste are called _______ because _______.

B. chemical senses; they detect chemicals in what we taste and smell.

Taste and smell is sensed through absorbing chemicals. Energy senses are sight, hearing and ouch. Every other senses do not exist. D is incorrect because signal is never sent chemically, it is always converted into an electric message.

1. Our sense of smell may be a powerful trigger for memories because

B. the nerve connecting the olfactory bulb sends impulses directly to the limbic system.

The nerve connected to the olfactory bulb is directly connected to the amygdala and hippocampus, which is why it's a powerful trigger for both emotions and memory.