It is too small to see but not too small to smell. Sometimes we can’t even see where the smell is coming from. An average person can smell maybe around 10,000 different odors. How do we do it? There are tiny sensors called ‘receptors’ found on cells that line the inside of our nose in something called the nasal cavity. These receptors are small measuring less than ten nanometers across. Is that small? Well it all depends. Only ten of these receptors would fit across a transistor that is found in your average computer chip. The odor molecules drift along in the air until they are sucked into our nose when we take a breath. If the odor molecule bumps into the right receptor, it binds to it and then transmits a signal to our brain. The signal goes through a special kind of cell called a nerve cell. Nerve cells are the wires throughout our body that takes all sorts of signals like smells, images and touch and then moves these signal to our brain. Once there, our brain processes that signal and ah ha! we realize that we have smelled something stinky.

Some of the stinkiest odor molecules are really stinky. One of the stinkiest is ethyl mercaptan (also known as ethane thiol). Skunks use ethyl mercaptans to keep enemies away and it is also used in natural gas to let us know when there is a leak. We can smell about 50 parts per billion of ethyl mercaptan in the air. Hmm is that a lot? Well not really. In one cubic foot of air (think of a cube that is one foot on each side) there are about 10²³ molecules of air. If we sniffed a small fraction of that lets say one cubic inch, it would take about 10¹³ molecules for of ethyl mercaptan for us to smell it. That seems like a lot but that is only ten nanograms! And there are a billion nanograms in a gram. Your average skunk weighs about two thousand grams so 10¹³ is a tiny, tiny amount.

Want to know more? Go to an interview with Christina Zelano.

Image Sources: C. Zelano, UC Berkeley | Answers.com