The senses help animals interpret their world. Some animals rely on unique senses. For example, bats and whales use echolocation (Ek-oh-loh-KAY-shun) — a sort of sonar system — to improve their understanding of the placement of things in their environment. Some fish can detect electrical fields around them. We humans rely on other ways to sense what’s in and around us.
Our sensory systems use signals coming to us from both outside and inside our bodies. Senses can also be shaped by experiences and feelings. It’s the brain’s role to make sense — literally — of all those incoming data. Indeed, most sensory information is meaningless until processed by the brain.
Some senses work from a distance, others only upon contact. For instance, we can see objects many kilometers (miles) away. But smell and taste rely on detecting chemicals in the air or in your mouth. To taste something, it needs to touch receptor cells in your mouth or other parts of the digestive tract.
Some senses work together. For instance, smell, touch and taste combine to give us flavor. Vision and hearing can work as a pair to help us read other people’s lips.
Experts vary on how many senses humans use. But below are the ones most commonly described.
Sight: This is how we understand what’s in front of our eyes. Eyes are the primary organs for sight. Light entering them activates light-sensing cells in the back of the eye. There are two types of these photoreceptors: rods and cones. Cones help us perceive color. Rods help with low-light (night) vision. Both types of receptors send electrical signals to the brain through the optic nerve. The brain transforms those signals into visual images.
Hearing: Sounds enter our bodies through our ears. Each outer ear is like a funnel. It collects sound waves arriving from different angles and directs them to the ear canal. The waves vibrate the eardrum. Its movements shift small bones in the middle ear. These send the vibrations to the inner ear, to a snail-shaped structure called the cochlea (KOKE-lee-uh).
The cochlea holds a liquid that moves in response to vibrations. The liquid’s motion will move nearby sensory cells called hair cells. Different hair cells respond to different sound frequencies. Their motion will then trigger an electrical signal that moves down the auditory nerve to the brain. It’s the brain, again, that interprets what this system has sensed.
Smell: Also known as olfaction, smell works by detecting scent molecules in the air. After entering the nose or mouth, these molecules bind to specific receptors. Those receptors send electrical signals down the olfactory nerve to the brain.
Taste: Like smell, taste is a chemical sense. The tongue is full of taste buds. But they appear in other places as well, including the lungs. These buds have sensory cells that respond to certain chemicals in food. Nerve fibers on the taste buds relay signals to the brain to help the body interpret what you’re eating. There are five basic agreed-upon tastes: sweet, salty, sour, bitter and savory (also known as umami). However, some scientists believe there may be more taste sensors, including one for fat.
Touch: Touch is one of the first senses to develop in babies. It plays a key role in helping infants bond with caregivers. The sense of touch relies on specialized neurons found throughout the skin. When stimulated, these neurons send signals to the brain.
Sometimes, touch is divided into specific categories. These include pressure, temperature, vibration and pain. But some experts argue that each of these is its own sense. Why? Because these sensations rely on different receptors and nerve endings.
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Proprioception: Your brain tracks when, where and how parts of the body bend and move through proprioception (PROH-pree-oh-SEP-shun). This sensory system has lots of moving parts. Neurons that sense body motions sit in the body’s muscles and tendons. They help inform the brain which parts are moving and in what way.
Proprioception helps you adapt to your environment. If you’ve ever been on a boat, when you get off you may find your body still feeling like you’re at sea. This is because proprioception helps you adapt to the movement of the ocean’s waves. Once back on land, your body uses proprioception to reorient itself to solid footing.
Vestibular sense: Somewhat related to proprioception, this sense is important for balance and spatial orientation. It’s what helps us stay on our feet and move smoothly. It also tracks changes in the head’s position and movements.
To do this, the vestibular system relies on organs in the ear that are filled with fluid. As the head moves, so does that fluid — allowing it to wiggle hair cells in the inner ear. The movement of those hair cells triggers signals to the brain about where the body is in space. For example, they help interpret if you are upright and unmoving, twirling or in the process of leaning over.
Other neurons in the brain can respond to help the body compensate for such movements. For instance, we may change our footing, arm placement or posture to keep from falling over.
Interoception: This is our sense of events happening inside us. Interoception collects information from internal organs, such as your heart, lungs, gut, bladder and kidneys. Motion, pain or other signals from our organs may help inform the brain about how hungry we are, whether we’re hot or if we’re scared (such as a rapid heartbeat). These signals can even warn when we may be about to vomit (have nausea) or need to pee (pressure in the bladder).
Power Words
More About Power Wordsactivate: (in biology) To turn on, as with a gene or chemical reaction.
angle: The space (usually measured in degrees) between two intersecting lines or surfaces at or close to the point where they meet.
auditory nerve: The nerve that carries electrical signals that represent sound from the ear to the brain.
bladder: A flexible bag-like structure for holding liquids. (in biology) The organ that collects urine until it will be excreted.
cell: (in biology) The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall. Depending on their size, animals are made of anywhere from thousands to trillions of cells.
chemical: A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O.
cochlea: A fluid-filled hollow tube in the inner ear of humans and many vertebrates that has a spiral shape. That shape lets different sound frequencies (wavelengths) stimulate particular regions of the spiral. This creates a sort of map for incoming sounds and enables animals recognize different pitches of sound.
cones: (in biology) A type of eye cell thatis part of theretina inside the back of the eye. These cellscan sense red, green or blue light. Recent research has uncovered evidence that many can sense white light — but only white light.
data: Facts and/or statistics collected together for analysis but not necessarily organized in a way that gives them meaning. For digital information (the type stored by computers), those data typically are numbers stored in a binary code, portrayed as strings of zeros and ones.
develop: To emerge or to make come into being, either naturally or through human intervention, such as by manufacturing. (in biology) To grow as an organism from conception through adulthood, often undergoing changes in chemistry, size, mental maturity or sometimes even shape.
echolocation: (in animals) A behavior in which animals emit calls and then listen to the echoes that bounce back off of solid things in the environment. This behavior can be used to navigate and to find food or mates. It is the biological analog of the sonar used by submarines.
environment: The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature andhumidity (or even theplacement of things in the vicinity of an item of interest).
fat: A natural oily or greasy substance occurring in plants and in animal bodies, especially when deposited as a layer under the skin or around certain organs. Fat also is a vital nutrient, though it can be harmful if consumed in excessive amounts.
flavor: The particular mix of sensations that help people recognize something that has passed through the mouth. This is based largely on how a food or drink is sensed by cells in the mouth. It also can be influenced, to some extent, by its smell, look or texture.
GI tract: Short for gastrointestinal tract. These are the organs — largely the stomach and intestines — that break down and absorb the nutrients needed by the body.
gut: An informal term for the gastrointestinal tract, especially the intestines.
hair cells: These are the sensory receptors inside the ears of vertebrates that allow them to hear. These actually resemble stubby hairs.
kidney: Each in a pair of organs in mammals that filters blood and produces urine.
literally: An adjective indicating that the phrase it modifies is precisely true. For instance, to say: "It's so cold that I'm literally dying,"means that this person actually expects to soon be dead, the result of getting too cold.
molecule: An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).
muscle: A type of tissue used to produce movement by contracting its cells, known as muscle fibers. Muscle is rich in protein, which is why predatory species seek prey containing lots of this tissue.
nausea: The feeling of being sick to one's stomach, as though one could vomit.
nerve: A long, delicate fiberthat transmits signalsacross the body of an animal. An animal’s backbone contains many nerves, some of which control the movement of its legs or fins, and some of which convey sensations such as hot, cold or pain.
neuron: The main cell type of the nervous system — the brain, spinal column and nerves. These specialized cells transmit information by producing, receiving and conducting electrical signals. Neurons also can transmit signals to other cells with chemical messengers.
olfaction: (adj. olfactory) The sense of smell.
optic nerve: A nerve that carries information, as electrical impulses, to the brain from the retina of the eye. The brain then translates those signals to images.
organ: (in biology) Various parts of an organism that perform one or more particular functions. For instance, an ovary is an organ that makes eggs, the brain is an organ that makes sense of nerve signals and a plant’s roots are organs that take in nutrients and moisture.
orientation: (v. orient) The deliberate arrangement of your position (of that of something else) relative to the cardinal directions (north south, east or west), to the ordinal directions (northeast, southeast, southwest or northwest) or to some landmark (such as the horizon, a particular street corner or a statue).
pressure: Force applied uniformly over a surface, measured as force per unit of area.
receptor: (in biology) A molecule in cells that serves as a docking station for another molecule. That second molecule can turn on some special activity by the cell.
rods: (in biology) A type of eye cell thatis part of theretinainside the back of the eye. These cells are rod shaped and sensitive to light. Although more sensitive to light than cone cells are, rods can not tell what color something is.
sea: An ocean (or region that is part of an ocean). Unlike lakes and streams, seawater — or ocean water — is salty.
sensor: A device that picks up information on physical or chemical conditions — such as temperature, barometric pressure, salinity, humidity, pH, light intensity or radiation — and stores or broadcasts that information. Scientists and engineers often rely on sensors to inform them of conditions that may change over time or that exist far from where a researcher can measure them directly. (in biology) The structure that an organism uses to sense attributes of its environment, such as heat, winds, chemicals, moisture, trauma or an attack by predators.
sonar: A system for the detection of objects and for measuring the depth of water. It works by emitting sound pulses and measuring how long it takes the echoes to return.
sound wave: A wave that transmits sound. Sound waves have alternating swaths of high and low pressure.
spatial: An adjective for things having to do with the space where something is located or the relationships in space between two or more objects.
system: A network of parts that together work to achieve some function. For instance, the blood, vessels and heart are primary components of the human body's circulatory system. Similarly, trains, platforms, tracks, roadway signals and overpasses are among the potential components of a nation's railway system. System can even be applied to the processes or ideas that are part of some method or ordered set of procedures for getting a task done.
taste: One of the basic properties the body uses to sense its environment, especially foods, using receptors (taste buds) on the tongue (and some other organs).
taste buds: A collection of 50 to 100 or so taste receptors.They’re found on the tongues of land animals. When certain chemicals in food or other materials trigger a response in these receptors, the brain detects one or more of five types of tastes —sweet, sour, salty, bitter or umami.A collection of 50 to 100 or so taste receptors.They’re found on the tongues of land animals. When certain chemicals in food or other materials trigger a response in these receptors, the brain detects one or more flavors — sweet, sour, salty, bitter or umami.
tendon: A tissue in the body that connects muscle and bone.
umami: One of the five major tastes (along with sweet, sour, salty and bitter). It has been described as savory but most people find the mild flavor hard to characterize. It is particularly prized as a flavor in Japanese cuisines.
unique: Something that is unlike anything else; the only one of its kind.
vibrate: To rhythmically shake or to move continuously and rapidly back and forth.
wave: A disturbance or variation that travels through space and matter in a regular, oscillating fashion.
Citations
Webpage: M. Barker, R. Brewer and J. Murphy. What is interoception and why is it important? Frontiers for Young Minds. June 30, 2021. doi: 10.3389/frym.2021.558246.
Video: Alila Medical Media. The Vestibular System, Animation. 2022.
Webpage: National Institute on Deafness and Other Communication Disorders. How Do We Hear? May 2015.
Journal: J.C. Tuthill and E. Azim. Proprioception. Current Biology. Vol. 28, March 5, 2018, p. R194. doi: 10.1016/j.cub.2018.01.064.
Webpage: University of Utah Genetic Science Learning Center. Proprioception: additional information. Accessed November 3, 2023.
Journal: C. Pfeiffer, A. Serino and O. Blanke. The vestibular system: a spatial reference for bodily self-consciousness. Frontiers in Integrative Neuroscience. Vol. 8, April 17, 2014. doi: 10.3389/fnint.2014.00031.
Magazine: D.V. Smith and R.F. Margolskee. Making sense of taste. Scientific American. Vol. 284, March 2001, p. 32.
Journal: A.J. Hudspeth. How hearing happens. Neuron. Vol. 19, November 1997, p. 947.
