In school, you learn that there are five senses: touch, smell, taste, hearing and sight. It turns out though that human beings perceive the world and gather information in more than just five ways. Scientists have established that there are nine verified senses, and some believe the actual number of ways that we sense is more than 20.
What Is a Sense?
So what exactly do scientists consider a sense to be? In simple terms, a sense is a system of gaining information. When you sense something, special cells in the body respond to physical stimulation and transmit signals to the brain that then interprets them, using the information in a number of ways. All of the following phenomena are generally included in the list of human senses:
Sight is seeing the world around you through specialized cells in the eyes. It involves detecting color with cone receptors and brightness with rod receptors.
Your sense of taste comes from a chemical reaction between substances and specialized receptors on your tongue. There are a variety of receptors that detect different types of tastes like bitterness, sourness, saltiness, sweetness and umami. The latter receptors taste an amino acid called glutamate, which is found in many meats.
Touch receptors in our skin sense the texture and feel of objects.
Pressure receptors tell your body when something external to you is exerting force.
Specialized receptors in the skin detect chemicals that are released by the immune system and trigger feelings of itchiness.
This sense allows you to detect whether something is hot or cold and to regulate your internal body temperature. Sometimes, scientists classify it as two separate senses: external temperature sensing by receptors in the skin and internal temperature sensing by receptors in the brain.
Vibrations caused by sound waves stimulate tiny hairs inside of the ears, which allow us to perceive sound.
Like taste, smell is fueled by chemical reactions detected by receptors in the nose. In order to sense flavors, both your senses of smell and taste are required.
This big word refers to a very simple sense–the one that lets you know where the parts of your body are all located at any given time. You rely on this sense to touch any part of your body without looking at it. Alcohol can impede proper proprioperception, which is why touching your fingertip to your nose is commonly used as a field sobriety test if you’re suspected of drunk driving. The term proprioception is derived from the Latin word for “one’s own,” which is “proprius.”
Nociception is the scientific term for sensing pain. Your body is home to three types of pain receptors: visceral receptors located in the organs, somatic receptors found in the bones and joints and cutaneous receptors situated in the skin.
Sensors in the muscles tell your brain when the tissue has contracted. When tension becomes great, sensations of pain can arise.
This sense is what makes it possible for you to maintain your balance and to know when your body is moving with increased speed or in a new direction. The receptors for this sense are located in the inner ear. Called the vestibular labyrinthine system, it is powered by the weight of tiny calcium carbonite deposits located on fine hairs and the movement of fluid in the ear canal.
Receptors located in the digestive system, the lungs and the bladder detect stretching, which can give you the sensation that you can’t take a full breath, have eaten too much or need to urinate. Other stretch receptors can detect when blood vessels dilate and have been linked to certain types of headaches.
Chemoreceptors use chemical reactions to detect the presence of natural and foreign chemicals in the bloodstream. It’s this sense that often leads you to vomit if you’ve drank too much alcohol.
Your sense of thirst lets you know when your body has become dehydrated and is in need of water.
This sense detects when food is needed to fill the stomach.
This weak sense allows humans to detect magnetic fields and is believed to help humans travel in the right direction. Scientists don’t fully understand how magnetoreception works in humans; however, some people believe the sense originates from iron stored in the nose.
Not all scientists agree that humans have the ability to sense time, but there is some evidence to suggest that there are special receptors in the brain that allow humans to sense the passage of time. Scientists do agree that the body has a natural internal clock that controls wake and sleep cycles, but it’s unclear if this is technically a sense.
Other Interesting Facts About the Senses
The simplified five-sense approach that is still widely taught in schools was developed by Aristotle, an Ancient Greek Philosopher.
One study that helped to prove that humans do have at least some ability to detect magnetic fields involved eliminating magnetic fields and then asking people to try and orient themselves to face the north, south, east and west.
In most cases, people are unable to do so properly without any magnetic field present. Other studies using visual imaging have shown that when a strong magnetic field is placed near a person, the brain does respond.
There was a very fascinating study that many scientists point to as proof, that time can be sensed. During the test, groups of people were asked to estimate when 3 minutes of time had elapsed. Adults aged 19 to 24 were able to do so with an accuracy of plus or minus 3 seconds.
Seniors aged 60 to 80 were an average of 40 seconds off, seeming to indicate that the ability to sense time might decline with age. Studies also show that individuals with ADHD and Parkinson’s disease have more difficulty perceiving time.
Many animals and other organisms use magnetoception much better than humans. Magnetotactic bacteria actually build natural magnets inside of their cells, so that they can sense direction in relation to the magnetic field of the Earth. The bacteria use the sense to link up and form long chains. It’s also magnetoreception that allows birds to travel in the right direction when they migrate.
The birds can actually see the magnetic field with the help of a substance in their vision receptor cells called cryptochrome. Cows also typically will stand north to south when out to pasture using magnetoreception. Sea creatures like sharks and stingrays use an organ called the ampullae of Lorenzini to detect electricity. This gives them keen magnetoreception and other abilities.
Some humans have a sense called synesthesia in which other sensory information is seen as a color. These rare individuals may see colors when they experience certain tastes, smell certain smells or hear certain sounds.