162. The Art of Smelling

Sometimes people really never remember to smell things. We are so busy thinking that we forget to smell what we eat, what we drink, how we smell to others, how are partner smells....how life smells.

Smell is a very direct sense. In order for you to smell something, molecules from that thing have to make it to your nose. Everything you smell, therefore, is giving off molecules -- whether it is bread in the bakery, onions, perfume, a piece of fruit or whatever. Those molecules are generally light, volatile (easy to evaporate) chemicals that float through the air into your nose. A piece of steel has no smell because nothing evaporates from it -- steel is a non-volatile solid.

At the top of your nasal passages behind your nose, there is a patch of special neurons about the size of a postage stamp. These neurons are unique in that they are out in the open where they can come into contact with the air. They have hair-like projections called cilia that increase their surface area. An odor molecule binds to these cilia to trigger the neuron and cause you to perceive a smell.

According to the book Molecular Biology of the Cell:

Humans can distinguish more than 10,000 different smells (odorants), which are detected by specialized olfactory receptor neurons lining the nose.... It is thought that there are hundreds of different olfactory receptors, each encoded by a different gene and each recognizing different odorants.

Each of the hundreds of receptors are encoded by a specific gene. If your DNA is missing a gene or if the gene is damaged, it can cause you to be unable to detect a certain smell. For example, some people have no sense for the smell of camphor.

When you smell many fruits or flowers, what you are smelling is esters evaporating from the fruit or flower. Esters are organic molecules. For example, the ester that gives a banana its smell is called isoamyl acetate, and the formula for it is CH₃COOC₅H₁₁. The primary smell of an orange comes from octyl acetate, or CH₃COOC₈H₁₇. Esters can now be made artificially, and that is where artificial flavors come from.

A big batch of cookies coming out of the oven. Your gym bag full of dirty clothes. How do you smell these smells and thousands more? It's your nose, of course.

Your nose lets you smell and it's a big part of why you are able to taste things. The nose is also the main gate to the respiratory system, your body's system for breathing. Let's be nosy and find out some more about the nose.

Nose Parts

The nose has two holes called nostrils. The nostrils and the nasal passages are separated by a wall called the septum (say: SEP-tum). Deep inside your nose, close to your skull, your septum is made of very thin pieces of bone.

Closer to the tip of your nose, the septum is made of cartilage(say: KAR-tel-ij), which is flexible material that's firmer than skin or muscle. It's not as hard as bone, and if you push on the tip of your nose, you can feel how wiggly it is.

Behind your nose, in the middle of your face, is a space called thenasal cavity. It connects with the back of the throat. The nasal cavity is separated from the inside of your mouth by the palate (roof of your mouth).

Getting the Air in There

When you inhale air through your nostrils, the air enters the nasal passages and travels into your nasal cavity. The air then passes down the back of your throat into the trachea (say: TRAY-kee-uh), or windpipe, on its way to the lungs.

Your nose is also a two-way street. When you exhale the old air from your lungs, the nose is the main way for the air to leave your body. But your nose is more than a passageway for air. The nose also warms, moistens, and filters the air before it goes to the lungs.

The inside of your nose is lined with a moist, thin layer of tissue called a mucous membrane (say: MYOO-kus MEM-brayne). This membrane warms up the air and moistens it. The mucous membrane makes mucus, that sticky stuff in your nose you might call snot. Mucus captures dust, germs, and other small particles that could irritate your lungs. If you look inside your nose, you will also see hairs that can trap large particles, like dirt or pollen.

If something does get trapped in there, you can probably guess what happens next. You sneeze. Sneezes can send those unwelcome particles speeding out of your nose at 100 mph!

Further back in your nose are even smaller hairs called cilia (say: SILL-ee-uh) that you can see only with a microscope. The cilia move back and forth to move the mucus out of the sinuses and back of the nose. Cilia can also be found lining the air passages, where they help move mucus out of the lungs.

Sniff, Sniff, Take a Whiff

The nose allows you to make scents of what's going on in the world around you. Just as your eyes give you information by seeing and your ears help you out by hearing, the nose lets you figure out what's happening by smelling. It does this with help from many parts hidden deep inside your nasal cavity and head.

Up on the roof of the nasal cavity (the space behind your nose) is the olfactory epithelium (say: ol-FAK-tuh-ree eh-puh-THEE-lee-um). Olfactory is a fancy word that has to do with smelling. The olfactory epithelium contains special receptors that are sensitive to odor molecules that travel through the air.

These receptors are very small — there are about 10 million of them in your nose! There are hundreds of different odor receptors, each with the ability to sense certain odor molecules. Research has shown that an odor can stimulate several different kinds of receptors. The brain interprets the combination of receptors to recognize any one of about 10,000 different smells.How Signals Get SentWhen the smell receptors are stimulated, signals travel along the olfactory nerve to the olfactory bulb. The olfactory bulb is underneath the front of your brain just above the nasal cavity. Signals are sent from the olfactory bulb to other parts of the brain to be interpreted as a smell you may recognize, like apple pie fresh from the oven. Yum!Identifying smells is your brain's way of telling you about your environment. Have you ever smelled your toast burning? In an instant, your brain interpreted the smell and a problem and you knew to check on your toast.You learned to associate a certain smell with burning and now your brain remembers that smell so you recognize it. Your sense of smell also can help you keep safe. For example, it can warn you not to eat something that smells rotten or help you detect smoke before you see a fire.

Tastes Great!Most people just think of the tongue when they think about taste. But you couldn't taste anything without some help from the nose! The ability to smell and taste go together because odors from foods allow us to taste more fully.Take a bite of food and think about how it tastes. Then pinch your nose and take another bite. Notice the difference? It's just another reason to appreciate your knockout of a nose!

Listen to the song by Paul Young " Love is in the air"

https://www.youtube.com/watch?v=HUaIdOsJqF8