Sensory Function Nerves
Cranial nerves (CN) I, II and VIII are primarily sensory related.
- CN I, the olfactory nerve, carries information regarding smell from the nose to the brain. Loss of the sense of smell may indicate damage to CN I, such as from a tumor, known as an olfactory groove meningioma, according to Mayfield.
- CN II, the optic nerve, carries visual information to the brain for processing. Loss of vision or perception may indicate damage to the optic nerve.
- The vestibulocochlear nerve, CN VIII, controls hearing and balance. Loss or a decrease of hearing may indicate nerve damage.
Motor Function Nerves
Cranial nerves associated primarily with motor function are IV, VI, XI and XII.
- CN IV is the trochlear nerve, which controls inward and downward eye movement. Damage can cause double vision.
- CN VI, or abducens nerve, controls outward eye movement. An interruption to the abducens nerve can cause double vision.
- Neck turning and shoulder movement are controlled by CN XI, or the accessory nerve. Damage can cause shoulder drooping and prevent head rotation.
- CN XII, hypoglossal, controls the ability to move the tongue in all directions. Damage can cause difficulty speaking and swallowing.
Mixed Function Nerves
Cranial nerves III, V, VII, IX and X have a mixture of motor, sensory and parasympathetic functions.
- CN III, oculomotor, controls upward, inward and downward eye movement and upper eyelid movement. In addition, it controls the pupil’s response to light. Damage to CN III may be revealed as a dilated pupil unresponsive to light, which may indicate brain death.
- CN V, or trigeminal, controls facial sensation and the ability to chew. Damage to CN V can cause a loss of sensation to your face or the ability to open and close your jaws.
- CN VII, the facial nerve, allows you to smile or frown, carries taste sensations from the front of your tongue to the brain and provides stimulus to the lacrimal and salivary glands. Damage may cause facial drooping.
- CN IX, glossopharyngeal, and X, vagus, are responsible for the gag reflex and the ability to speak and swallow. These are sensations from the pharynx and larynx. In addition, Merck Manuals Online Medical Library reports the vagus nerve controls muscles in your internal organs, such as your heart.
Treatment for Cranial Nerve Damage
Treatment for cranial nerve damage depends on the location, cause and extent of damage. Potential causes include tumors, injuries and infections. Infection of the nerve can cause swelling, which puts pressure on the nerve and interferes with the nerve functioning properly. According to the UC San Diego Health System, treatment options include steroids for swelling, medications for bacterial or viral infections and surgical intervention to release the pressure on the nerve.
Treatment options for tumor-related CN damage include surgery and radiation. For a head trauma injury, intervention may include immediate surgery to repair structural damage, such as a crushed skull, and relieving the pressure on the affected nerve or nerves.
Recovery from cranial nerve damage also varies, depending on the location and extent of the damage and can range from a few weeks or months to years. Damage caused by infections and pressure from swelling may resolve with treatment. Severe injuries may be permanent or life threatening.
Mayfield: Meningiomas https://www.mayfieldclinic.com/PE-MENI.htm
Merck Manuals Online Medical Library: Testing Cranial Nerves https://www.merckmanuals.com/home/sec06/ch096/ch096a.html
UC San Diego Health System: Facial Nerve Disorders https://health.ucsd.edu/specialties/surgery/neuro/cnd/facial/