Cranial Nerves Lab Evaluation at Cape Fear Community College

C. Abducens The abducens nerve (Cranial Nerve VI) innervates the lateral rectus muscle, which is responsible for abducting the eye—moving the eyeball outward, away from the nose. Injury to CN VI results in the inability to abduct the affected eye, causing medial deviation (esotropia) and horizontal double vision.

B. Superior rectus The superior rectus muscle elevates the eye and assists with medial rotation and adduction. CN III provides motor innervation, enabling upward gaze. If weakened, the eye will have difficulty looking upward, especially in a straight-ahead position. C. Medial rectus The medial rectus adducts the eye, moving it toward the nose. Controlled by CN III, this muscle is essential for convergence, such as when reading. Damage causes difficulty crossing the eyes or eyes drifting outward (exotropia). D. Inferior rectus The inferior rectus depresses the eye and contributes to adduction and external rotation. Innervated by CN III, it helps move the eye downward. Dysfunction impairs downward gaze, impacting tasks such as walking down stairs. F. Inferior oblique The inferior oblique elevates the eye and assists in external rotation when the eye is adducted. CN III controls this muscle. Weakness results in vertical diplopia and difficulty looking up when the eye is turned inward.

A. Oculomotor The oculomotor nerve (Cranial Nerve III) innervates the majority of the extraocular muscles: the superior rectus, medial rectus, inferior rectus, and inferior oblique. These muscles allow the eyes to move up, down, and medially, and assist in eye rotation and focusing. Damage to CN III may cause ptosis, pupil dilation, and the eye resting “down and out.”

Cranial nerve IV (trochlear nerve) controls the superior oblique muscle, allowing the eye to move downward and inward. To test CN IV, the nurse asks the client to follow an object with the eyes and assesses downward–inward gaze. Dysfunction may cause diplopia and difficulty going down stairs or reading due to impaired eye movement.

The glossopharyngeal nerve (CN IX) is evaluated by observing swallowing and soft-palate movement. Asking the client to swallow and watching the soft palate move up and down assesses gag reflex and pharyngeal muscle function. Proper elevation indicates intact CN IX function, essential for swallowing and airway protection.

A. Glossopharyngeal The glossopharyngeal nerve (CN IX) provides sensation to the posterior tongue, soft palate, and oropharynx, playing a key role in the gag reflex and airway protective reflexes. Before extubation, airway competence must be confirmed—adequate gag reflex and swallowing ability indicate readiness. During an awake fiber-optic intubation, the glossopharyngeal nerve is often blocked to reduce gagging and improve patient comfort.

E. Superior oblique Cranial nerve IV (Trochlear nerve) innervates the superior oblique muscle. This muscle depresses the eye and rotates it inward, especially when the eye is adducted. Damage to CN IV results in vertical diplopia (double vision) and difficulty looking down, such as when reading or walking downstairs. Patients may tilt their head away from the affected side to compensate.

Cranial nerve II is the optic nerve, responsible for vision. The nurse tests CN II by assessing visual acuity, most commonly using a Snellen eye chart. Each eye is tested separately to identify deficits in central vision. This helps determine clarity of sight and identifies potential neurological or ocular problems such as optic neuritis or visual field loss.

B. Glossopharyngeal The glossopharyngeal nerve (Cranial Nerve IX) provides parasympathetic innervation to the parotid salivary gland via the otic ganglion. This nerve stimulates saliva production from the parotid gland. Damage to CN IX can result in decreased salivation and impaired swallowing.