Cranial Nerve I: Olfactory Nerve
What’s unique about the Olfactory Nerve?
The Olfactory Nerve is the first cranial nerve and is the shortest of all of the cranial nerves. It has a purely sensory function, transmitting our sense of smell, otherwise known as olfaction.
What is the function of the nerve?
Sensory: Sense of smell
What are the signs of dysfunction?
Symptoms of impact to the olfactory nerve vary:
• Anosmia, complete loss of smell
• Dysomia (also called phantosmia), unpleasant or strange odors that occur spontaneously
• Hyposmia, partial loss of smell
• Parosmia, distorted sense of smell (for example, familiar foods may smell like chemicals or mold)
How might this nerve be impacted?
Several conditions can affect the olfactory nerve:
• Sinus infection and nasal polyps
• Tobacco use
• Poor dental hygiene
• Environmental toxins and chemicals like insecticides
• Severe head injuries, including concussions
• Medications like antibiotics
• SARS-CoV-2, the virus that causes COVID-19
• Head and neck cancer
• Diabetes
• Alzheimer’s disease
• Brain tumor
• Parkinson’s disease
• Epilepsy
How can you work with this nerve?
• Notice the midline crista galli, the attachment site of the falx that the optic bulb sits beside, the frontal lobe, and the ethmoid bone, and offer wide space for decompression for each.
• Visualize the pathway, from the mucosa, through the cribriform plate of the ethmoid bone, arising in the olfactory bulb and becoming the olfactory tract beneath the frontal lobe.
• Notice the quality of potency moving through the nerve.
• Hold space for any held patterns along the pathway to shift.
The olfactory bulb sits on top of the cribriform plate of the ethmoid bone.
Holes in the cribriform plate house downward projections from the bulb into the nasal epithelium which pick up scents that enter via the nostrils or the mouth.
At the end of these projections are cilia, which are the small hair like extensions at the terminal end of the olfactory sensory neuron.
Odorous particles that are dissolved in the mucus layer stimulate the cilia.
Messages are passed up via the dendrites.
Messages then move through the cell bodies.
The cell bodies pass the message on to the axons. The axons then synapse with a mitral cell in the olfactory bulb above the bone.
It is the mitral cell that carries information on the individual odors back to the brain.
Posteriorly, the olfactory bulb thins to become the olfactory tract, which runs inferiorly along the frontal lobe.
As it approaches the brainstem, the olfactory tract divides into olfactory stria.
The olfactory stria communicate with the uncus, where information enters the olfactory cortex. The olfactory cortex has connections to many other areas, allowing it to decipher different smells.