Taste & Smell ( ESSAY )

Now we are going to started diving into our "world of senses". How we experience our six major senses all boils down to one thing : "sensory cells translating chemical, electromagnetic, and mechanical stimuli into the "language" of our nervous system, which is action potentials". The process that changes chemical, electromagnetic, and mechanical stimuli into action potentials is called "transduction" and every organ of our body each have a different way to do it. Our vision functions with the help of photoreceptors, cells that detect light wave, while our senses of touch, hearing, and balance uses mechanoreceptors that detect sound waves and pressure on your skin. But our sense of taste or gustation, and smell or olfaction, works by sensing mechanical senses. They call on the help of chemoreceptors on our nose and mouth to interpret that stimuli into action potentials. The thought of our senses is just 5 or 6 are wrong. We actually have tons of secondary senses, like the ability to sense temperature, pain, acceleration, etc. That is all considered senses. Our most primitive and fundamental are our sense of taste and smell. Believe it or not, the sense of taste and smell are most strong at birth. As we get older, those two senses "decline", so the older we are, the less "good" our sense of smell and taste is. Tastes and smell are also powerful at activating memories, triggering emotions, and alerting us to danger. Now lets start to analyze how you can detect chemicals in the air and then turn them into the thoughts of "hmmm nice smelling pizza". All process starts as you and I sniff the molecules (or chemicals) of, lets say pizza. That means that the molecules are floating in the air, and that also means that the molecules are in a gaseous form, or volatile. And yes, when you smell poop, there is actually poop particles in your nose right there and then. Those pizza molecules that are floating in the air are vacuumed up your nose. Most of these is filtered out by your nose hair but not all of them. A few make it all the way to the back of the nose and hit your olfactory epithelium. This is your olfactory system's main organs. But here's the wonder of our sense of smell : Each olfactory neuron has receptors to detect a single kind of smell. At any given thing, like the pizza that you are smelling, there are hundreds of chemicals, like the thymol of the oregano, the butyric acid of the cheese, and much more. All the receptors that are "turned on" by the chemicals in the air, sends a signal to the brain, then the brain combined that all and tell you that, wow this is a very delicious smelling pizza. Scientist estimate that our 40 million different olfactory receptors neurons helps us identify about 10.000 different smell, maybe even more. Now just imagine a piano with thousands of keys able to produce millions of different combinations of sounds, you'll get an idea of how amazing our sense of smell are. So once the smell of pizza hit the olfactory neuron, it sends it to your brain through the olfactory tract to the olfactory cortex of the brain. From there, the pizza-smell hits the brain through two avenues : One brings the information to the frontal lobe, where they can be consciously identified, like oh, the smell of pizza; while the other pathway heads straight to your emotional ground control -- the hypothalamus, amygdala, and other parts of your limbic system. This emotional pathway is quick, intense, and fast to trigger memories. If the odor is associated to danger, like the smell of smoke, it quickly activates your sympathetic nervous system's "flight of fight" response. And these same intellectual and emotional apply to taste as well. Because taste is basically 80 percent smell. That's why when you couldn't smell, you usually also couldn't taste. As you chew your food, air is forced up your nasal passages, so your olfactory receptor cells are registering information at the same time your taste receptors are, so you are basically tasting and smelling at the same time. So, it's true when you caught a bad cold, or just hold your tongue so that air couldn't pass through your nose, you could still taste some food, but it would not be the same. So you can hold your nose and taste that something is sweet, but you could not pinpoint that it is caramelized sugar or just plain old sugar. Most of your taste buds are located on your tongue, but some is also located on your cheeks and other places on your mouth. As soon as you take a bite, all of the sensory information is quickly sorted by the ten thousand or so taste buds located on your tongue, mouth, and upper throat. Oh yeah, by the way, the taste maps of your tongue, that you probably have seen, are wrong. Those tongue diagrams date back to the early 1900s, when German scientist D.P Hanig tried to measure the sensitivity of different areas of your tongue for sweet, salty, sour, and bitter. The map that are resulted are pretty subjective, pretty much just reflecting on what his volunteers felt like they were sensing. While it's true that taste can be grouped into sweet, salty, bitter, and sour, all your taste buds, wherever they are can still taste all of those tastes. A little experiment. Try putting salt on the tip of your tongue, where the taste map tells us that that region is for tasting sweet, you would still taste the salt in all it's glorious saltiness.


P.S. : I mostly gathered the information to create this post from Crash Course. If you don't know 'em, check out their youtube channel, it's awesome, I'll promise you that.