Think you of the fact that a deaf person cannot hear. Then, what deafness may we not all possess? What senses do we lack that we cannot see and cannot hear another world all around us?
-The Orange Catholic Bible, Dune
A sense, broadly defined, is the physiological capacity of an organism to perceive its environment. It is the interface between brain and surroundings that allows the organism to adapt its actions.
One of the most persistent medical myths is that of the five senses. Most first graders can rattle them off by rote: sight, hearing, smell, taste, touch. While it is a good start, it is an unnecessarily limiting categorization. First of all, it is extremely anthro-centric. Animals have many senses that we do not, such as the ability to detect the proximity of objects through electrical fields (sharks) and an internal compass that can detect the Earth’s magnetic field (birds). Other animals possess such sensitive traditional senses that the human versions seem primitive in comparison, such as how dogs can construct a 3D map of their surroundings just by sniffing the air. In the great sphere of possible sensory experiences, the entire human sensory spectrum amounts to a tiny pinprick.
But even stopping at the edges of the human body, there are a great many additional senses that don’t get the same amount of recognition as the “big five.” Some experts might tell you that they are all subsets of the sense of touch, but I believe they deserve their own independent study, and lumping everything into “touch” is a gross oversimplification. Without further ado, here are five interesting and important senses not contained within the traditional big five:
Also known as the kinesthetic sense, proprioception is the ability to tell where your body is located in space. While information from sight and touch is also used to calculate the positions of your limbs, you have an innate ability to sense where your body is even without enlisting senses other than proprioception.
You can “feel” this sense with a simple experiment: close your eyes and move your arms around slowly. You’ll notice that even though you cannot see your limbs and you are not moving them fast enough to get much information from changes in air pressure, you still know almost exactly where your arms are located relevant to the rest of your body. That is called proprioception.
There are documented cases of individuals who have lost this sense. With time, they can learn to walk, but only if they can see where their legs are. Turn out the lights and they will collapse. If you’ve got the seven minutes, this documentary clip about a man who lost his proprioception is well worth your time:
Also known as the vestibular system, this is your sense of balance. It is how you know that you are right-side-up or upside down. It works in conjunction with other senses but also has its own unique method of leveling contained in the inner ear. Small tubes filled with fluid act as your own personal accelerometer, able to tell the direction and speed of your head’s rotation. Other parts of the inner ear can even detect linear acceleration.
Malfunction of the vestibular system is what causes vertigo, a form of permanent dizziness. Temporary disruption is easily achieved by spinning around in a circle for a bit – you can easily tell that your sense of balance is at least somewhat independent from your sense of touch.
This is your physiological sense of pain. It is different from the sense of touch because it uses different receptors. There are nerve endings called nociceptors throughout your body that are specialized to detect everything from mechanical distress to extreme heat. This network triggers a broad range of physical and mental reactions, including the subjective experience of pain.
You actually have two pain networks. The first, known as “Fast Pain,” detects mechanical distress and extreme temperatures. It travels by a type of fast-signaling nerve fiber that has a special relationship with your spinal cord, enabling the unthinking reflex motion that lets you quickly pull your hand away from a hot stove. In contrast, “Slow Pain” is associated with chemical distress, goes more directly to the brain along slower-signaling nerve fibers, and is felt as an aching or throbbing pain over a large and nonspecific area of the body.
“Oxygenoception” (not a technical term)
Lining the walls of your aortic arch and the branch of your carotid artery (the split artery that sends blood up to your brain) are clusters of specialized cells canned peripheral chemoreceptors. Their function is to constantly monitor the concentrations of oxygen and carbon dioxide in your blood. When all is well, you do not notice this sense, even though your nervous system is hard at work regulating your breathing to maintain an optimum balance. But too much carbon dioxide triggers that horrible feeling of suffocation that occurs if you hold your breath for too long.
“Vomitoception” (not a technical term)
There is an area of the medulla in your brain called the chemoreceptor trigger zone. It is connected with another brain structure called the area postrema. One function of these two organs can be classified as chemoreception – they are constantly monitoring your blood for signs of toxins that indicate you have eaten something poisonous. Detection creates the “red alert” that signals your stomach to evacuate its contents.
So you know when you start getting that feeling that you need to puke? That’s actually a result of a specialized sense organ in your brain that is hard at work monitoring the toxicity of your blood at all times. Take a moment to appreciate that next time you’re praying to the porcelain goddess.