Today in class we learned about the functioning of olfactory nerves. It was really quite interesting, especially to find out how the olfactory system is organized. Let’s begin in the nasal cavity. Here, present in the mucus layer, are projections of the olfactory receptor cells. Each receptor cell is only capable of binding to one specific type of odorant molecule. These receptor cells travel through the porous bone separating the skull from the nasal cavity, and feed into a specific glomerulus. Glomeruli are located in the olfactory bulb, and have multiple receptors feeding into them. However, each glomerulus receives input from only one receptor type. In the glomerulus, the receptor neurons make excitatory connections with other cells, whose own axons project into the olfactory cortex in the brain. What is cool here is that there are about 1000 different types of olfactory receptor neurons, which each have their own proteins. This means that there are most likely 1000-2000 genes encoding for olfaction. It has been shown that this is not a combinatorial system like that developed for immunity.
Another cool thing I learned was that every time someone blows their nose, they are losing part of their brain. Seriously though, it’s not quite as bad as it sounds. What is really happening is that you are losing the olfactory receptor cells that protrude out into the mucus layer inside the nasal cavity. The neat thing is that these cells are able to regenerate, which is unusual for other human neural cells. I was wondering, if perhaps, due to the organization of the olfactory nerves, regeneration is able to happen because of the interaction between the olfactory receptor neurons and the glomeruli. Perhaps the protruding parts of the cells are able to be regenerated because they are actually only part of the cell, not the entire cell. If this is true, then if the glomerulus were destroyed, would that permanently destroy the sense of smell? Or would the glomerulus be capable of regeneration, like the olfactory receptor cells that feed into it?