Psychology 101: Intro to Psychology

How do taste, touch and smell work? Also, what is proprioception? Throughout this lesson, you'll get a detailed description on each of these remarkable senses.

Vision and hearing help us to navigate the world; to locate objects, to communicate and to avoid potential danger. Our other senses--taste, touch and smell--may seem less critical, but they still make valuable contributions to our rich sensory experiences. The sense we have of what's going on inside our body, known as proprioception, isn't taught to schoolchildren as one of the 'five senses,' but it's still an important part of how we make sense of our bodies' actions and reactions.

Taste and smell are pretty closely related to one another; if you've ever had a stuffy nose, you've probably noticed that certain foods just don't taste as good or as interesting when you can't smell them at the same time. This is because the areas of the brain that process these two senses are right next to each other. Taste and smell both work by having specific receptors designed to detect the presence of substances like sugar, acid, other molecules and compounds.

There are five main taste sensations that our tongues can detect: sweet, salty, sour, bitter and umami (also known as savory). You're probably familiar with the first four. You've definitely tasted umami, but you might not think of it as its own separate taste; it's that meatiness and earthiness present in soy sauce, cheese, ripe tomatoes and mushrooms. Each of the five basic tastes is associated with a different kind of taste bud, or receptor on the tongue that tells neurons to fire off signals when certain substances touch them. People have anywhere between 2,000 and 8,000 taste buds on their tongues; taste buds die off and regrow quickly, living on average for only about five days. For taste buds that detect sweetness, that substance is the sugar molecule; for taste buds that detect saltiness, that substance is sodium. Some umami taste buds respond to the chemical MSG, sometimes used to enhance flavor, particularly in Asian cuisines.

The tongue can feel additional sensations that are not exactly tastes, but which are still made by compounds activating certain receptors. Fattiness and minty-ness are examples of this; there are receptors which respond to certain compounds in fatty and minty foods. The burning sensation you feel when you eat spicy food or drink alcohol is another kind of nerve reaction not directly related to taste.

As for smell, your nose has odor receptor neurons that respond to tons of different substances that can be floating in the air. A neuron will only fire if a particular odor molecule comes along and activates it; this is known as a lock-and-key system. Even the human nose can tell apart almost 10,000 odors, and our sense of smell is way less developed than other mammals'. As we age, our noses gradually get less sensitive; this happens with taste as well.

Touch and proprioception are separate senses both considered part of the somatosensory system, which reports sensations of pressure, body position and pain. Your skin, which is actually considered the body's largest organ, has four different kinds of receptors that respond to different things. You can feel pressure, hot, cold and pain; everything else you feel is a combination of these basic sensations. For example, the feeling of your skin being wet is caused by a combination of a pressure sensation with a cold sensation. You also have specialized neurons inside your body that fire off signals when your muscles move to help you keep track of where your limbs are. This is known as your sense of proprioception. Your vestibular system also helps you keep track of where your body is; this is controlled by the fluid inside your ears. If you have an ear infection or a cold, sometimes this can mess with your vestibular system and cause you to feel dizzy or disoriented.

So we've talked about three senses; taste, smell and touch, including proprioception. Taste and smell are related, and both involve receptors that respond to particular kinds of molecules and compounds. Touch involves receptors on the skin that detect pain, hot, cold and pressure and combine these four sensations into all the feelings we have. We also have neurons inside our bodies that help us know where the parts of our body are.