Human senses

Pause for a moment and observe. What are five things you can see? What four things can you physically feel? What three things can you hear? What two can you smell?

And what is one thing you can taste? By doing this simple exercise you make observations about the world around you using five of your senses. When you look around, you use your eyes and your sense of sight. Once light reaches the eyes, special cells convert it into visual information and then transform that information into signals. Nerve cells then carry these signals to a part of your brain that interprets them and forms an image — and that is how you see things!

Sight is our strongest sense, so the majority of people rely mostly on their visual perception when experiencing the world. What about the sense of touch? You feel touch through your body’s largest organ — the skin! Your skin is full of nerve cells. Some are specialised to detect pain, temperature, or different textures.

Parts of your body have many more of these cells than others. That’s why your hands or your face are more sensitive than, say, your thighs. These nerve cells then send signals to the brain, which interprets them and causes you to take an action — for example, quickly remove your hand from the hot stove. Remember the things you listened out for at the start? All sounds are vibrations, and your sense of hearing allows you to detect and recognise these vibrations as specific sounds.

Your ears act as funnels for these vibrations, directing them via your eardrum and the three smallest bones in your body, to your inner ear. There, specialised hair-like cells translate vibrations into electrical impulses which travel to the brain via nerve cells. The brain translates these impulses; allowing you to understand different sounds! What about when you smell things? You breathe in...

and air containing scent molecules enters your nose. Some of these molecules attach to hair-like receptors up in your nose. This triggers signals to travel up to your brain, which tells you what the smell is, whether it’s pleasant, familiar, new,... Taste is perhaps the simplest of our senses — we can only detect five different tastes: sweet, bitter, sour, salty and umami. All of these are detected by separate receptors found on those tiny bumps on top of your tongue — the taste buds.

These receptors also send signals to the brain, which then interprets them. This interpretation could then tell us whether we like the taste, or if it might be dangerous for us — like the unusual sourness of spoiled milk means it’s not a good idea to drink it. Let’s try another exercise. Close your eyes and stretch out your hand. Even though you can’t see it, you most likely know exactly where your hand is.

How? There are receptors in your muscles, tendons and joints that detect your movement and position at all times. This is another sense you have — proprioception. Proprioception often works together with other senses, such as visual perception, and it makes tasks like walking, much easier. All senses require specialised cells that detect signals from the environment, translate them and send them to the brain, which then makes sense of it all.

Sight, touch, hearing, smell, taste and proprioception are our most obvious senses and they interact to form a more complete experience of the world. But scientists believe that we could have as many as 21, or even 53 senses! Can you guess what those senses could be?