Our senses enable us to navigate and make sense of our environment, but more importantly, they enable us to find food and mates, and to avoid danger. Our sense of taste and smell help us to learn what’s poisonous and what’s edible. Our sense of touch tells us when our feet are touching the ground, and that fi re is hot. And as an added bonus, our senses allow us to hear and see beautiful things, to feel the softness of a kitten’s fur or take pleasure in the touch of others and to enjoy what we’re eating and drinking. Our combination of senses offer us a unique and varied experience of the world that no other living creature completely shares. Mammals, birds, fi sh and insects all have their own unique experience of their environment that we can never share. While we usually hear of our five senses, we now know that those five (sight, hearing, touch, taste and smell) are only the most central. The actual number is still in dispute. The one, and most important organ involved in all of our senses is the brain. The senses collect the data, but it’s the brain that interprets and makes ‘sense’ of it all. And it does it at amazing speed.
Humans are very visually oriented. We make a lot of our decisions based on sight. It’s how most of us navigate the world. But the fact that blind people live otherwise normal and fulfilling lives tells us it is no longer necessary for survival. Our vision evolved because it gave us an advantage over potential predators and information about our environment that made it easier to overcome difficulties. To see, specialized cells in our eyes receive light, which activates chemical responses and sends signals to the brain. The brain then analyzes these signals, decoding the color, shape and intensity; deciding if it’s a person, place or thing and finally giving you an image – all in just milliseconds. Most of us see in color, though we are only able to perceive a small part of the light spectrum – colors from red to violet. Not everyone sees the same colors, though. Some people are color-blind, they are not able to detect all the wavelengths. Most color-blind people have trouble distinguishing red, yellow and green from each other.
Hearing was the last sense to evolve, emerging as animals left the sea for land. Sound is produced by vibration, and the number of vibrations per second determines its pitch. Sounds above human hearing are called ultrasonic, those below are known as subsonic. Dogs, bats and some insects are capable of ultrasonic hearing. Whales and elephants produce subsonic sounds, but it is unknown for sure if they hear them. Our ears are divided into 3 parts. The outer ear (the part you see) serves to enhance and focus the vibrations received, funneling them into the middle ear. The middle ear amplifies the vibrations and sends the signals to the inner ear, where they are converted to electrical impulses and sent to the brain. Cats have some of the best hearing of all mammals, able to hear into the ultrasonic range. Humans use hearing primarily for communication. We also enjoy hearing sounds, just as we enjoy what we see. Humans are not alone in appreciating music – dogs have been shown to be calmed by classical music, and cows react to relaxing music by producing more milk. Elephants are able to keep a beat, perhaps better than humans.
The senses of taste and smell are closely entwined. You may have noticed that food seems to have little taste when you have a cold. This is because the odor of the food is integral to its taste. Mouthfeel and temperature also affect our perception of flavor. The taste-buds on our tongues and elsewhere in our mouths and throats sense flavor molecules in our food. There are multiple versions of these cells, and each reacts to a certain aspect of flavor – sweet, salty, sour, bitter and savory are the primary sensations. We may also have receptors for fat and other taste sensations. Our nose brings in odor molecules with every breath. Our noses are lined with nerve cells that bind to these molecules which send electrical impulses to the brain. Dogs are known for their excellent scent detection. While we have the ability to detect smell almost as well as they do, dogs use their senses differently. It is the most important sense in the dog’s world, in the way that vision is for us.
Touch receptors are found all over (and inside) our body. Touch is really only one of a group of somatosensory senses. We have receptors for every type of skin contact we experience – pressure, temperature, pain and more. We also have receptors that tell the brain our position and control movement. Proprioception, the sense of where our body is in space, combines with all the above senses to coordinate our moves and together allow us to navigate and understand our world.
