Science News

What Is a Smell, And How Does The Nose Work ?

Sun, 13th Feb 2005

Part of the show Science of Sex, Smell and Pheromones...

 

Chris - Your research is orientated towards the sense of smell and olfaction. What is a smell?

Peter – A smell is a chemical. The chemicals float around in the air around us and can tell us what is nearby. We have special receptors in the nose that can pick up these chemicals. This causes a response, which is then transmitted to our brain.

Chris – What about when there are lots of smells mixed up in the air? Your nose must get bombarded. How does the brain work out what it is smelling?

Peter – Coffee, for example, has around one hundred different odour components to it. When these go up someone’s nose, lots of cells are activated. It’s the pattern of these activated cells that the brain recognises as coffee odour. A slightly different pattern will show the difference between a normal coffee and an elaborate one.

Kat – I’ve noticed that food doesn’t taste right when I have a cold. Is that related?

Peter – Despite what you would think, a lot of the flavour of food comes in through the nose. When you chew, chemicals are released into your mouth and some go up the back of your throat into your nose. Your tongue is not as refined at telling flavours apart, so your nose is an important part of tasting. When you have a cold, your nose gets blocked up and the chemicals from the food can’t get through. This is why food can taste bland or different.

Chris - Why do dogs have such an acute sense of smell?

Peter – There are two ways in which a sense of smell can be better. One way is that the dog can be more sensitive and pick up smaller concentrations of a chemical, such as in a scent trail. The second way is to have more of the different types of receptors. This gives them a finer-grained ability, so they can tell things smell differently even when we might think they are same.

Chris – If you look at the brain of a dog, over a third of it is dedicated to smelling. This is in contrast to humans, which have sight as our main sense. Dogs really do live in a olfactory world.

Peter – Yes, and this is the same with most animals. Our sense of smell has actually been decreasing over evolutionary time. We have remnants of genes coding for these different receptors, but they don’t work anymore. For that reason, they are called pseudogenes. Humans now have about 350 types of receptors. Rats might have about 1000 receptors picking up smells, which indicates the different smell worlds we live in.

Kat – I love the smell of my boyfriend’s t-shirts. Does that mean that he’s the man for me?

Peter – It could do. It’s well known that people have different body odours, and it’s these odours that dogs pick up on when trying to follow someone. It has also been suggested that people unrelated to you have particularly attractive body odours. Alternatively, when you get to know someone really well, you could just get to like everything about him, including the way he smells.

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