Smell

Human nose
See also parts two and three.

Not everyone smells the same. It seems to be true that every human has their own bouquet, other than identical twins. Even dogs can’t tell identical twins apart by smell, and dogs smell far better than humans. Maybe in both senses of the word. How would we know? We don’t smell especially well.

We smell well enough to survive and thrive in our environmental niche, and no more. Our bodies by nature don’t waste their finite resources where they’re not needed. The proteins deployed in the sensory system, and the neurons used to process the subsequent sensory information can be used elsewhere. Still, on average, we are estimated to be able to discriminate about 10,000 different odors.

Smells are chemicals. They are distinct arrangements of molecules; particles with particular shapes and distinct modes of vibration. The particles have to be small enough to float in the air, so we can breathe them into our noses. Then we dissolve them in the mucus lining our olfactory tissue in the region called the nasal mucosa. Humans have about ten million receptor cells, which have a stem tipped by a knob that has hairs. The actual smell receptors are on the tiny hairs.

Each receptor is attended by a neuron, whose job is to send a signal to the brain when a smell particle is identified. Although we have hundreds of different kinds of odor receptors, for identifying hundreds of molecules, only a few kinds are on each hair. The types, numbers and distribution of receptors vary through the population. We don’t all smell the same.

Smell has the shortest path to the brain of all the senses. The information goes directly into the limbic system, a most ancient part of the brain. The limbic system is strongly involved in basic motivation, emotions and memory. This region has a rich network of connections with other parts of the brain, going both ways.

Not all smells are passed on to the brain. Some we simply can’t detect, not having the required receptor. Sometimes the neuron doesn’t fire, if the system is saturated by that smell, for instance. Not all smells are passed to our awareness if the limbic system decides it’s not necessary. So a lot of the smells that we react to, we don’t even notice.

We all have a different smell. Likewise, we all have a different sense of smell. Not everyone smells the same.

rjb

About arjaybe

Jim has fought forest fires and controlled traffic in the air and on the sea. Now he writes stories.
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5 Responses to Smell

  1. mixedupmeme says:

    All I know is that this time of year my nose is itching and running from the cedar allergies. 🙂

  2. emmylgant says:

    I am intrigued by smells short path to the limbic system… How have we used this to protect ourselves or move fast? We say funny things like I smell danger, or I smell a rat. In French they say ” I can’t smell him” to mean “I can’t stand him.” Interesting..

  3. arjaybe says:

    I’m going to have to think about that for a while. It would be natural for me to interpret “I can’t smell him” as “I can’t figure him out” or something similar. I’ll have to think about how it equates to “can’t stand.”

    rjb

  4. Pingback: Smell – Part Two | Green Comet

  5. Pingback: Smell – Part Three | Green Comet

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