The olfactory nerve is a collection of nerve rootlets which extends from the olfactory bulb to the olfactory epithelium, the area of the nose which actually intercepts scents. The nerve cells in this part of the nose are chemosensitive, responding to chemical signals which are converted to electrical impulses which are carried up the olfactory nerve to the olfactory bulb. Once these impulses reach the microregion in the olfactory bulb which corresponds with the nerve cells which were stimulated, the signals are passed on to various areas in the brain, and the owner of the nose is allowed to perceive the smell.
Also known as the first cranial nerve, this nerve is the shortest of the cranial nerves. It is also the only cranial nerve, other than the optic nerve, which does not meet up with the brainstem. People have two olfactory nerves, one on each side of the face, and these nerves can be tested independently by plugging one side of the nose and exposing a patient to various odors. It helps to use a strong or pungent aroma for a stronger response.
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This nerve is one of the most basic, reflecting the early origins of the olfactory system, which is one of the oldest sensory systems in most living organisms. It is also very vulnerable to damage, as it extends beyond the hard protection of the skull to the softer areas of the face, which means that it can be injured as a result of facial trauma. Someone with a broken nose, for example, may have an injured olfactory nerve as well.
Exposure to harsh chemicals, strong odors, and certain types of infections can also lead to olfactory nerve damage. Since patients may only damage one olfactory nerve at a time, they may not be immediately aware of the damage, attributing a diminished sense of smell to a stuffy nose or not even noticing the decreased sensitivity to odors. A doctor can diagnose olfactory nerve damage by exposing a patient to strong odors and monitoring the patient's reaction.
This nerve makes up an important part of the larger olfactory system, the system which allows organisms to intercept and perceive smells. The sensitivity of the olfactory system is largely determined by the size of the olfactory epithelium; the larger the epithelium, the more smells an organism can isolate, and the more precisely an organism can differentiate between different smells. Although humans may feel like they are living in a world of smell sometimes, they in fact have comparatively weak olfactory systems when compared to many other animals.