smell2.html

How do you Smell?

Many things need to happen for you to be able to sense a smell. First there must be an odor source. Molecules from the odor source must go up your nose - swept in on the intake of breath or in the act of sniffing. (Twice as much of the air you breathe reaches your olfactory membrane when you sniff.) Those odor molecules are swirled around and warmed up in your nasal cavity with the aid of the turbinate bones. They then are trapped in the mucus surounding your olfactory membrane. The odor molecules then interact with chemoreceptors on the cilia of your olfactory membrane. Those receptors send a message to your brain via the olfactory bulb. Your brain then interprets the information it receives, compares it to past experiences and you think, "rose," or "smelly shoe," or whatever it was that released the odor molecules in the first place.

Here's a more detailed look at those chemoreceptors.

The picture on the left is a magnification of part of the olfactory membrane. The bright blue shapes are the receptor cells. The finger-like projections you see on them are the cilia we were talking about above.

The picture on the right is a magnified view of the cilia. The chemoreceptors are represented by the notches or holes on the cilia. The odor molecules are the colorful shapes floating around among to the cilia. Scientists think that the shape and size of the odor molecule allow it to interact with only a few receptors. Our brain can tell which receptors detect molecules and so can tell what the smell is.

Smell and your brain.
The chemoreceptors have just sent a message through some nerves into the olfactory bulb of your brain. From there the message first goes to the limbic system. The limbic system is the part of your brain that controls your moods and emotions. It is also where memories are stored. This close connection to the limbic system makes smells a powerful trigger for vivid memories and/or emotions. None of your other senses are so intimately associated with memory or emotion. Next time you are on a walk keep your "nose open" ... and see what memories smells can evoke.

"Smells are surer than sights or sounds to make your heartstrings crack."
- Rudyard Kipling

Definitions:

Chemoreceptors: Chemical sensors on the cilia of the receptor cells.
Cilia: Short hair-like structures that project from the surfaces of some cells.
Limbic system: The portion of the brain that controls our moods, emotions, and storage and retrieval of memories.
Nasal Cavity: The empty space inside and behind your nose.
Odor molecules: Molecules capable of being detected by your nose's chemoreceptors.
Olfactory bulb: The first part of the brain to receive olfactory sensory inputs.
Olfactory membrane: Layer of sensory cells in the upper rear of the nose.
Proboscis: The external part of your nose.
Receptor cell: Ciliated cell in the olfactory membrane that senses odor molecules.
Turbinate bones: The thin, scroll-like boney plates extending from the walls of the nasal cavity. Their shape causes the air to swirl around in the nasal cavity as you breath it in.

All information and programs subject to change without notice.