Brain and Smell

The olfactory nerve or CN1, the first of 12 cranial nerves located within the head, is responsible for decoding sensory stimuli that result in the brain interpreting the data as ‘smells.’ Like the optical nerve, the olfactory nerve does not connect with the brain stem—the only two cranial nerves for which this is true. Apparently, smell exists only inside your own brain. Your sense of smell gives rise to the perception of odors. Millions of olfactory receptor neurons are found in a small patch of tissue (olfactory epithelium) located in back of the nasal cavity. The neurons function as sensory signaling cells. Each neuron has cilia (tiny hair-like projections) that are in direct contact with air. Airborne particles that enter the nasal cavity interact with these neuron receptors. Common odors that you are accustomed to, such as your own body odor, are less noticeable to you than external or uncommon odors due to habituation. The sense of smell tires quickly after continuous exposure to an odor but recovers rapidly after the odor stimulus is removed. Environmental conditions can impact the process of ‘smelling.’ For example, when the air is cool and dry, odors usually are more easily distinguishable by the brain. Blunt trauma damage to the olfactory nerve can lead to a reduced or even absent sense of smell. Nasal pain typically will still register in the brain, however, because pain is transmitted by the trigeminal nerve.