What are the Cranial Nerves?

Human EyeBy Ashly Westrick, Research Manager

This past Tuesday, June 17, 2013, we posted a blog about a new study from New York University that will investigate the use of eye tracking technology to assess patients with hydrocephalus. Eye tracking technology utilizes the movements of the eyes to assess the function of the cranial nerves. In hydrocephalus, cranial nerves can be damaged due to intracranial pressure. The researchers hypothesize that analyzing the movement of the eyes could be used to detect hydrocephalus. This research utilizes the cranial nerves but what are the cranial nerves and which specifically help control the eyes?

We hope this blog is both educational and supplemental to Dr. Uzma Samadani’s summary of their current research study.

What are the Cranial Nerves?

There are twelve cranial nerves located in the brain:

I. Olfactory: functions in smell.II. Optic: sensory impulses for sight.III. Oculomotor: motor nerves – raises eyelids, rotate eyes, adjust amount of light.

IV. Trochlear: smallest cranial nerve – helps control eye movement.

V. Trigeminal: largest cranial nerve – sensory input (touch and pain) from the face, chewing.

VI. Abducens: originates from the pons – controls abduct of the eyes (moves the eyes away from the nose).

VII. Facial: facial expressions, impulses to salivary glands, impulses to taste receptors.

VIII. Vestibulocochlear: sensory nerve with two branches. The cochlear branch is responsible for hearing and the vestibular branch is responsible for balance.

IX. Glossopharyngeal: tongue and pharnyx.

X. Vagus: carries impulses from the throat, esophagus, thorax, and abdomen to the brain. Motor fibers supply the heart and many smooth muscles and glands.

XI. Accessory: carries impulses to the muscles of the throat, muscles to the back and neck (controls muscles used in head movement).

XII. Hypoglossal: motor nerve – moves the tongue in speaking, chewing and swallowing.

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The four cranial nerves involved in vision and movement of the eyes are the optic (I) nerve, oculomotor (III) nerve, trochlear (IV) nerve and the abducen (VI) nerve. The optic nerve is the sensory nerve for vision. It transmits information from the eyes to the brain. The oculomotor, trochlear, and abducen nerves are responsible for movement of the eyes. The oculomotor nerve is a motor nerve responsible for controlling movement of the eyes such as raising the eyelids, rotation of the eyes and dilation of the pupils. The trochlear nerve is the smallest of the cranial nerves and helps control the eyes moving down and out. The abducen nerve originates from the pons and abducts the eyes or moves the eyes away from the nose.

The Cranial Nerves and Hydrocephalus

Damage and weakening of these nerves from intracranial pressure can result in eye misalignment. Adults can experience double vision from this and children may see double at first but, without treatment, can develop a lazy eye. The abducen nerve is especially susceptible to injury due to hydrocephalus. Damage to this nerve can cause the eyes to cross (esotropia). Increased intracranial pressure can produce pressure on the optic nerve, damaging the nerve. Swelling of the optic nerve due to hydrocephalus is called “papilledema” which can result in reduced vision, reduced color vision, and visual field loss. (Read our blog on papilledema.)

The pressure and damage to the cranial nerves due to intracranial pressure can affect vision and movement of the eyes. Using eye tracking technology, the researchers hope to be able to assess the function of the cranial nerves and from this be able to assess the intracranial pressure. Learn more about the study and if you might be eligible to participate. In addition, you can learn more about vision and hydrocephalus by checking out our fact sheet Eye Problems Associated with Hydrocephalus.

References:

Cranial Nerves. Yale University School of Medicine, Yale Center for Advanced Instructional Media. Last revised: March 22, 1998. http://www.yale.edu/cnerves/

 

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