What are cranial nerves?

The 12 cranial nerves extend from your brain and brain stem, responsible for helping you control different motor and sensory functions.
The 12 cranial nerves extend from your brain and brain stem, responsible for helping you control different motor and sensory functions.

Twelve cranial nerves extend from your brain and brain stem, responsible for helping you control different motor and sensory functions. Cranial nerves facilitate communication between the brain and other parts of the body, mainly to the head and neck region.

Cranial nerves come in pairs on both sides of the brain and brain stem. Each one is numbered based on the place in the brain where they emerge, from front to back. When these nerves end up damaged and start malfunctioning because of an illness or injury, it affects your body’s ability to move and feel. Cranial nerve disorders are also called cranial neuropathies.

The 12 cranial nerves and their functions are:

  1. Olfactory nerve — It controls your sense of smell.
  2. Optic nerve — It carries visual information from your retina to your brain.
  3. Oculomotor nerve — It controls most of your eye movements along with the way your pupil constricts and the ability to keep your eyelid open.
  4. Trochlear nerve — It feeds nerves to the major muscle around your eyes that controls how they rotate.
  5. Trigeminal nerve — It provides sensation to your face and mouth along with motor control of their functions.
  6. Abducens nerve — It feeds nerves to the lateral rectus muscles of the eyes that control their lateral movements.
  7. Facial nerve — It controls muscles responsible for generating your facial expressions. It also provides taste sensations to two-thirds of your tongue and mouth.
  8. Vestibulocochlear nerve — It transmits sound and balance information from your inner ear to your brain.
  9. Glossopharyngeal nerve — It takes in sensory information from your middle ear, tonsils, pharynx, and the rest of your tongue.
  10. Vagus nerve — It is responsible for various tasks like sweating, your heart rate, muscle movements in your mouth, and making sure your larynx remains open for breathing.
  11. Spinal accessory — It controls specific functions of your neck and shoulders.
  12. Hypoglossal nerve — It controls your tongue movements for speech, eating, and swallowing.

Signs and symptoms of cranial nerve disorders

Cranial nerve issues can show up in people of any age. The symptoms you might experience depends on each cranial nerve’s function. Some of the most common signs that can indicate a cranial nerve disorder include:

  • Pain in different regions of the body
  • Tingling sensations in places like your arms, legs, or neck
  • Skin sensitivity when touched
  • Vertigo
  • Hearing loss
  • Loss of smell
  • Inability to control your facial expression
  • Problems with speech
  • Trouble swallowing
  • Weakened or paralyzed muscles

Types of cranial nerve disorders

Some examples of common disorders that are related to your cranial nerves include:

Trigeminal neuralgia

This condition results from a malfunctioning of the trigeminal cranial nerve. You experience severe facial pain, typically due to an artery's abnormal positioning that puts pressure on the nerve. It can feel like short bursts of stabbing pain in the lower part of your face.

Bell palsy

You typically experience paralysis or weakness on one side of their face when the facial cranial nerve stops functioning correctly. Bell palsy, or Bell’s palsy, can be brought on by an immune disorder or a viral infection. You may lose the ability to taste things with the front of your tongue on the side of your face that is affected.

Internuclear ophthalmoplegia

Damage to the lower part of the brain stem can lead to issues with your horizontal eye movement, sometimes leading to double vision. This cranial nerve disorder usually occurs when there is an injury to the fibers connecting the oculomotor nerve, the trochlear nerve, and the abducens nerve. Internuclear ophthalmoplegia often occurs in people who’ve had a stroke or in younger people with multiple sclerosis.

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Causes of cranial nerve disorders

Various conditions can lead to problems in how cranial nerves function, including:

  • Injuries to the head
  • Infections like Lyme disease and shingles
  • Tumors
  • Lack of blood supply
  • Pressure placed on the nerve
  • Medical disorders that cause deterioration of the nerve cells, like multiple sclerosis
  • Disorders that cause inflammation in your blood vessels
  • Toxins like mercury
  • Certain medications

Tests for cranial nerve disorders

The kind of test requested by your doctor will depend on your symptoms. Tests typically performed to diagnose neuropathy include:

  • A neurological exam to check your reflexes, sensations, balance, and mental state
  • An electromyogram (EMG) to measure the level of electrical activity in your muscles when they are active and at rest
  • Computerized tomography (CT) and magnetic resonance imaging (MRI) scans that allow doctors to get an image of your brain
  • Skin and nerve biopsies to check the extent of damage to your cranial nerves function
  • Hearing tests
  • Angiography to get pictures of your heart and blood vessels

Treatments for cranial nerve disorders

Some cranial nerve disorders can clear up on their own. Other recommendations from your medical provider might include medication for treating the symptoms of your neuropathy. They may also recommend surgical intervention to repair damage. Cranial nerve disorders can cause extensive damage so it is important to get tested and get treatment.

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Medically Reviewed on 1/4/2021
References
Johns Hopkins Medicine: "Multiple Cranial Neuropathies."

Merck Manual: "Bell Palsy."

Merck Manual: "Internuclear Ophthalmoplegia."

Merck Manual: "Overview of the Cranial Nerves."

Merck Manual: "Trigeminal Neuralgia."

Penn Medicine: "Cranial Nerve Disorders: Conditions and Diagnosis."

UC Davis LibreTexts: "Brief Overview of Cranial Nerves."