The gustatory sensory system enables you to be aware of chemical composition and flavors of foods. If you “tasted it” – your gustatory system was responsible for that (well, with some help from your olfactory system).
How does the Gustatory System work?
Let’s hop a ride on a piece of chocolate and follow it through your gustatory system. It doesn’t have to be chocolate. It could be a piece of kale… No? You’d prefer chocolate? Let’s see why…
Pop that piece of chocolate in your mouth. The first thing it comes into contact with is your tongue. Your tongue is covered with little bumps called papillae. Each papilla has a little fluid-filled hole in the top, and a little bit of chocolate mush is swept inside. The inside of the papilla contains your taste buds (most papillae have 3-5 taste buds, but some types of papillae have several thousand taste buds inside!).
Taste buds are bud-shaped structures made up of gustatory (taste sensing) cells – anywhere from 10-50 cells per bud. Each cell has receptors that connect with substances with a particular chemical structure – and upon doing so, activate a nerve impulse.
The five chemical structures that your taste cells can detect are:
- Umami (or, savory)
The buds are surrounded by nerve cells that detect pain and heat. These cells are responsible for the pain sensation triggered by eating steaming hot stew, or by eating stew with lots of chili peppers (the chemical capsaicin found in hot peppers and other spicy things causes a pain sensation), or by biting your tongue when eating stew.
(Stew apparently has a lot more pain-triggering potential than chocolate. Let’s get back to chocolate.)
Your liquified chocolate mush comes into contact with all these gustatory cells. Some of the cells have glucose receptors, making them “sweet cells.” The glucose in the chocolate connects with the glucose receptors in the sweet cells, and the cell fires off a nerve signal: “Glucose detected! This thing is sweet!”
The sweet signal races along its pathway until it hooks up with one of the cranial nerves. It’s off to the brain.
The nerve signal carrying the “sweet” signal, along with any and all other taste signals inspired by your piece of chocolate, are carried along the cranial nerves on their way to the gustatory cortex. If it was chocolate with 72% cocoa solids, it’s likely to have triggered some “bitter” gustatory cells. If it was chocolate studded with pop rocks, it will have induced some “sour” signals. If it was chocolate laced with MSG, it will have triggered some “umami” gustatory cells. Either that, or it will have triggered vomiting once the “sweet + umami” signal combination hits your brainstem. That’s where gustatory signals head first.
Gustatory signals – like most other sensory signals – travel first to your brainstem, the clearinghouse and determiner of your unconscious reactions. If the taste is perceived as too intense or unpleasant, the result is nausea and the desire to vomit (or actual vomiting).
Your brainstem also contains the amygdala, the seat of emotional memory and reaction. If your piece of chocolate has the same chemical taste signature as the chocolate you shared with your best friend right after you finished an intense ten-hour hike together – it will evoke powerful memories of confidence, accomplishment and strong bonds of friendship. On the other hand, if your chocolate has a similar chemical taste signature as the chocolate frosting on the cake at your 6 year old birthday party where you didn’t get any good presents, lost all the games and wet your pants – you’re probably not going to want another bite, no matter how “objectively” tasty the chocolate is.
After the brainstem, the final destination of the gustatory signals is the gustatory cortex, where the signals from all the gustatory cells converge. In order to round out the five tastes and different layers of intensity, the smell signals from the olfactory system contribute their input here, too. Now you’ll be able to consciously savor the sweet taste of your chocolate.
What happens when it doesn’t work right?
Some people naturally have significantly more papillae than average. Anyone with a high volume of papillae will sense tastes with much more intensity than the norm. Chocolate that to an average person tastes sweet will taste SUPER sweet to them. A sour lemon will taste extraordinarily sour. The increase in papillae means an increase in the pain cells surrounding them, and so these taste-sensitive individuals will also be super-sensitive to spicy or hot foods. They actually feel the heat at triple the intensity of the average person biting into the same salsa.
Alternatively, the tactile sensory system and the proprioceptive sensory system can impact how a person experiences and deals with food (making it look like a gustatory system issue).
Issues with the tactile system can make people under-sensitive or over-sensitive to the texture of food. Mom! The sardines are too slimy!
Issues with the proprioceptive system can make people under-sensitive or over-sensitive to the physical experience felt in their joints while chewing. People who are over-sensitive may avoid crackers like the plague, whereas people who are under-sensitive will seek stimulation from popcorn, carrots, hard pretzels… the crunchier, the better.
See here for more details on Sensory Processing Disorder, how it manifests and what to do about it.