Olfactory Nerve

What is the olfactory nerve?

Your olfactory nerve is the first cranial nerve (CN I). It’s also part of your autonomic nervous system, which regulates body functions. This nerve enables your sense of smell. Cranial nerve 1 is the shortest sensory nerve in your body. It starts in your brain and ends in the upper, inside part of your nose.

What is the function of cranial nerve 1?

CN I makes it possible to detect scents, odors, aromas and more. Substances that smell give off tiny molecules. Inhaling moves these molecules into your nose. There, special cells (olfactory receptors) detect these molecules. The receptors relay this information to your brain through your olfactory nerve and allow you to perceive smell.

How does my sense of smell work?

Your olfactory system enables sense of smell in two ways:

• Nostrils: Substances that smell give off tiny molecules that can stimulate olfactory receptors. Receptors engage in specific combinations, enabling you to identify different types of smells.
• Back of your throat: Chewing food or taking a sip of a drink also releases molecules that help you smell. These molecules travel up your throat to the olfactory receptors in the back of your nose.

Your olfactory mucosa plays a significant role in your ability to smell. This membrane is in the upper part of your nasal cavity and contains different types of cells:

• Olfactory receptor cells, which support two processes: dendritic process and central process. Dendritic processes propel cells toward tiny hairs in your olfactory mucosa where they stimulate olfactory cells. Central processes direct cells in the opposite direction.
• Sustentacular cells, which provide support to nearby tissue.
• Basal cells, from which both olfactory receptor cells and sustentacular cells develop.

What is the anatomy of the olfactory nerve?

Your olfactory nerve is one of two nerves (visual nerve or cranial nerve 2) that originate directly from your cerebrum. This is the upper part of your brain. Other cranial nerves start in the lower parts of your brain, including your midbrain, pons and medulla oblongata, collectively referred to as your brainstem.

Olfactory nerve fibers travel a short distance to an area in the upper part of your nose (olfactory bulb). Before reaching your olfactory bulb, the nerve fibers pass through your cribriform plate. This spongy, lightweight skull bone separates your nasal area from your brain.

What are symptoms of impaired olfactory nerve function?

Issues that affect your olfactory system can cause:

• Anosmia, complete loss of smell.
• Dysosmia (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.

What conditions can affect cranial nerve 1?

Medical conditions and other situations that may affect olfactory nerve function include:

• 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 coronavirus (COVID-19) disease.
• Head and neck cancer.
• Diabetes.
• Alzheimer’s disease.
• Brain tumor.
• Parkinson’s disease.
• Epilepsy.

How does COVID-19 affect my olfactory system?

Up to half of the people with COVID-19 experience loss of smell. Researchers are still exploring why. But it’s possible that viral infections, like SARS-CoV-2, the virus that causes COVID-19, damage olfactory receptors. Many people regain their sense of smell. But it can take several months.

How can I prevent issues with CN I?

It might not be possible to prevent certain conditions from affecting your sense of smell. Complications from neurological disease or brain tumors may be unavoidable.

Preventive measures that are within your control include:

• Avoiding dangerous activities that could result in a brain injury.
• Getting the COVID-19 vaccine.
• Protecting your nose from chemical exposure by wearing a mask.
• Quitting smoking, vaping or other tobacco products if you use them.
• Brushing your teeth and flossing regularly.
• Staying current with treatments for conditions that can affect your olfactory system.
• Using protective equipment, like helmets, during sports to avoid a concussion.

When should I call a healthcare provider about problems with my olfactory nerve?

You should contact your healthcare provider if you notice:

• A change in the way things smell.
• Sudden loss of sense of smell.
• Foul odors with no cause.

It’s important to seek medical attention for these symptoms. They can raise your risk for health and safety issues that include:

• Eating too much food or not enough if you can’t smell it.
• Missing signs of danger, like a gas leak, smoke from a fire or food that has gone bad.

A note from Cleveland Clinic

Your olfactory nerve is the first cranial nerve (CN I). This nerve enables your olfactory system and sense of smell. Many conditions can affect cranial nerve 1, including COVID-19, diabetes and Alzheimer’s. It’s important to see your healthcare provider for difficulties with your sense of smell. They can let you know if it’ll come back or return to normal. They may also discuss ways to stay safe and healthy without it.