Are there more senses

Some say we have seven senses, while others put the total at nine, ten, or twelve. It all depends on how you define things.

The idea of five classical senses dates back at least to Aristotle, himself a rather classy guy. In De Anima Of the Soul he argues that, for every sense, there is a sense organ. Because when you start counting sense organs, you get to six right away: the eyes, ears, nose, tongue, skin, and the vestibular system. We now know that the vestibular system, located in the inner ear, is an integral part of how we balance ourselves, but it also plays a critical role in vision, allowing us to keep our two eyes focused on things even while our heads are moving about.

Instead of a sense organ, each separate sense really only requires a different kind of sensory receptor. In the skin alone, there are at least four different kinds of sensory receptors: those for touch, temperature, pain, and proprioception or body awareness.

A sensory receptor is a specialized cell that sends electrical signals to the brain in response to the type of stimuli the cell is optimized for. The rods and cones in the retina are sensory receptors. They send signals when stimulated by light of various wavelengths and intensities. This belief is so ingrained that even the scientifically literate will treat it as taken-for-granted common knowledge. Today, the five senses are considered such an elementary truth that it is sometimes used as a point of consensus before writers embark on more mysterious or contentious topics.

If only it were that simple. One, somewhat vague, definition might argue that a human sense is simply a unique way for the brain to receive information about the world and the body. If that is the case, then we can claim with confidence that there are certainly more than five human senses.

First consider the senses that relate to the position of our bodies. Close your eyes, and then touch your right forefinger to your left elbow tip. How did you do it? Somehow you knew where the end of your finger was and you also knew the position of your left elbow. Proprioception is possible thanks to receptors in our muscles known as spindles, which tell the brain about the current length and stretch of the muscles. Now imagine you are blindfolded and I tilted you forwards slowly.

This is thanks to the fluid-filled vestibular system in your inner ear, which helps us keep balance. This system also gives us our experience of acceleration through space, and it links up with the eyes, making it possible to cancel out our own motion. There are also numerous senses providing us with information about the inner state of our bodies.

The most obvious of these are hunger and thirst, inner body pain, and the need to empty the bladder or bowel. Examples are flavour, which the brain constructs from gustatory taste and olfactory smell data, and wetness, which is created from touch and temperature. Your brain actually predicts what you might see before you see it, based on past experience, the state of your body and your current situation.

It combines its predictions with the incoming sense data from your retinas to construct your visual experience of the world around you. You experience them with your brain.