Every day you experience hundreds of smells, some are familiar and comforting, some are an unwelcome surprise, some you hardly notice, but how do they work? What makes warm coffee smell like warm coffee, why does your house smell different to newcomers and how do we replicate smells? Here’s the basics on a sense that we often forget the importance of.
The Chemosensory System
Put simply, the chemosensory system are your chemical senses. They’re the systems which detect a variety of stimulants and give off biological responses. Taste is a chemosensory system, as is your sense of smell.
The reason you feel happy when you taste your favourite food or disgusted when you smell your friend’s fart, or scared or sickly when you smell something unnatural or deathly, is all a result of your chemosensory system detecting a stimulant and providing a biological response.
Sensory Cells
Sensory cells called olfactory neurons are what make your sense of smell work. There’s a patch of olfactory neurons behind your nose, at the top of the nasal passage, relatively close to the size of a postage stamp.
Each olfactory neuron has one odour receptor and each of the hundreds of receptors is encoded by a specific gene. Each gene helps you to detect a certain smell. It’s possible for genes to be damaged or be missing. If this is the case, you could be unable to detect a certain smell. A common case of this is not being able to smell camphor.
There’s trillions of smells in the world, many more than the amount of receptors in your nose. Different molecules can stimulate a variety of receptors which send a unique set of signals to your brain by a process called sensory transduction. Your brain recognises these unique combinations of signals as a particular smell.
Your brain can also, over time, get used to familiar cells. The reason for this may be so that you can recognise new (potentially bad) smells easier. That’s why when you leave your house for a while and come back it might smell more like when you first moved in. It’s also because all the smelly little molecules are hanging around waiting for you to open a window and let them out.
Esters – the smelly little molecules
Olfactory neurons are special as unlike most neurons, they are open to the air. They’re also covered in cilia – hair-like projections that help to increase the neuron’s surface area and catch odour molecules called esters.Esters are molecules that evaporate from objects. Different smelling objects give off different esters, which give them different smells. Esters are usually light and volatile – which means they evaporate easily and float in the air.
The ester given off by a banana for example is called isoamyl acetate. Nothing evaporates from steel (it’s a non-volatile solid) so, if you didn’t know, steel has no smell.
An Ester is chemical compound derived from an acid in which at least one hydroxyl group is replaced by alkyl group. We can create esters artificially; this is how we make artificial flavours and scents.
Smelling, or Olfaction to be Fancy
Olfaction is the chemical reception that forms your sense of smell. You smell because of your olfactory system – your nostrils, ethmoid bone, nasal cavity, olfactory epithelium (layers of thin tissue covered in mucus), your olfactory neurons and receptor cells.To smell something, molecules from that thing have to journey into your nose. What are these molecules? Esters. Everything you smell is giving off esters.
Esters reach your olfactory neurons via two routes – your nostrils and the little channel that connects the roof of your mouth to your nose.
Ever had a bad cold and mucus ends up building up in your throat? It’s come through that channel (eew). It’s also the reason why when you have a blocked nose or bunged up face that your sense of smell and sometimes even your sense of taste are less pronounced; because you’re blocking your sensory cells from touching these molecules.
So How does smell Work?
- Objects that smell give off molecules called esters.
- Different objects give off different esters.
- You have hundreds of teeny cells at the back of your nose that catch these esters and send signals to the brain to tell you which combination you’re smelling by a process called sensory transduction.
So, next time you’re sniffing something – maybe one of our scented candles, think about all the brave little esters that make it to your nose to let you know which scent you’re sense of smell is recognising.
Think of all your tiny little olfactory neurons that are doing a great job of catching those esters, so that you can enjoy Happy Piranha’s wide range of awesome smelling scented candles.
Try not to think too much about the fact that everything you’re smelling are all giving off molecules at the same time, as it can make the world seem a very busy and confusing place.
Smelly facts
- Fish are great at smelling. They detect dissolved substances in water with both the taste and smell senses. Historically they were thought not to be able to smell. This was until 1924 when a guy called Fritz Strieck proved that the Common Minnow can smell just fine. Previously it was thought that smell only detects volatile, airborne substances and that taste detected dissolved substances.
- It was previously thought that humans could distinguish more than 10,000 different smells, though some research now estimates it may be more than one trillion.
- Bears and elephants are some of the best sniffers as far as mammals go. Some bears have been observed to follow a scent to food up to 18 miles away and polar bears can smell a seal through 3ft of ice. Here’s some of the best animal smellers.
