Senses are our windows on the world

Our senses give us information about things we come across in the environment, such as what a thing is, how much of it there is and where it is. We have five senses:

• Smell
• Vision
• Hearing
• Touch
• Taste

Smell

The world is a smelly place. Some smells are nice, others are not so pleasant.

In fact, our sense of smell is all about chemistry. Dr Marie Migaud is a senior lecturer in organic chemistry at Queen’s University Belfast. She knows all about the science of smells - how the sense of smell can vary from person to person and why some things are smellier than other things.

“When you smell something from a dish, the molecules are evaporating from the dish and making their way to your nose,” she says. “They are being detected inside your nose by receptors.”

For example, if you smell the spice cinnamon, molecules of cinnamaldehyde (C9H8O), the chemical that smells of cinnamon, make their way to your nose and are detected.

“We are able to smell up to 10,000 types of smells,” says Dr Migaud. “We have roughly 2,000 receptors. They’re at the side of the nose and the top of the buccal cavity.” (That’s the cavity at the back of the mouth.) “Not everyone has the same receptors. We’re all slightly different,” says Marie. This explains why there are so many different types of perfume on the market.

What’s interesting is that you can’t have taste without smell – they are both linked. That’s why when you have a cold and your nose is blocked, food tastes bland. Looking at food gives people an appetite, but smelling food makes people salivate.

Touch

We also experience touch through many thousands of receptors. These sensory receptors are embedded in our skin and they relay information about our environment to our brains.

The concentration of touch receptors in our finger tips is actually higher than anywhere else on our bodies. This is because we use our hands to sense so much. In fact, there’s more of our brain dedicated to the sensors in our fingertips than in our legs and arms put together.

We also have more pain sensors than any other nerve endings. There are about 200 per square centimetre of your skin surface, all connected to your brain via your spinal cord.

Taste

We detect taste with receptor cells which are clustered into taste buds, connected to the surface of the tongue.

There are five different sensations of taste:

• Sour
• Sweet
• Bitter
• Salty
• Umami (the response to salts of certain acids like monosodium glutamate [MSG], a flavour enhancer used in some processed foods)

Our sense of taste protects us from unsafe foods – rotten food often tastes (and smells) revolting, so we don’t eat it.

On the other hand, things like chocolate usually taste really good. The sweet taste and fatty texture of chocolate appeal to our built-in taste preferences. The fat in the cocoa butter also creates a melt-in-the-mouth sensation, as chocolate has a melting point of about 34 or 35 degrees, a few degrees lower than our own body temperature.

Learn more:

Learn more about the senses on ThinkQuest

Read how the five senses work at the UK science museum

Put your senses to the test with the BBC’s senses challenge

Science of disgust

The sense of disgust is involved with the rest of our senses. It’s one of nature’s ways of keeping us out of danger, by making us want to avoid contaminated or diseased things.

SCOPE checks out the science of disgust with the help of celebrities Aidan Power, Kathryn McKiernan amd Pamela Flood.

Sight: If we compare the sight of a bowl of blue coloured water to the sight of a bowl of raw egg with red sauce in it, most people will think the egg looks much more disgusting. That’s because blue objects are usually not alive and are unlikely to carry disease, whereas the texture of the egg and red sauce suggests things like puss, mucus and blood – in other words, disease.

Smell: Our second comparison is between sweaty gym gear and stink bombs. Sweat doesn’t smell good but it doesn’t indicate disease. However stink bombs contain sulphur, a chemical released by bacteria and therefore associated with disease.

Touch: SCOPE compares the feel of some grapes in wallpaper paste and the feel of some wriggling maggots. Although the grapes in paste are harmless, their sliminess could suggest things like body parts. But because the maggots are alive, there’s a chance that they could be disease-carrying creatures so are deemed more disgusting.

Did you know? Girls are usually more disgusted by these things than boys. This is to do with their innate mothering and nurturing role – mothers need to prevent their children eating things like maggots.

Learn more about the feeling of disgust