Cranial Nerve Exam

Olfactory: Function

afferent impulses for sense of smell

Optic: Function

afferent impulses for vision and visual acuity

Occulomotor: Function

efferent impulses for eye movement, eyelid elevation, and pupil constriction.

Trochlear: Function

Somatic motor fibers to the superior oblique muscle, which controls eye movement and helps rotate the eyeball.

Trigeminal: Function

Sensory impulses from the face and anterior two-thirds of tongue. Motor fibers for mastication.

Abducens: Function

Efferent impulses for lateral eye movement, innervating the lateral rectus muscle.

Facial: Function

Controls muscles of facial expression, provides taste sensations from the anterior 2/3 of the tongue, and supplies glands for saliva and tears.

Vestibulocochlear/Auditory: Function

Transmits sound and balance information from the inner ear to the brain.

Glossopharyngeal: Function

Provides taste sensations from the posterior 1/3 of the tongue, controls pharyngeal muscles, contributes to swallowing and salivation, impulses from chemoreceptors in the carotid body, (O2, CO2, respiratory rate) impulses from baroreceptors of carotid sinus (blood pressure)

Vagus: Function

Controls autonomic functions, including heart rate, digestion, and respiratory rate; provides sensation from the throat and voice box. Carry general somatic sensory information from small area of skin on external ear. Carry proprioceptor fibers from muscles of larynx and pharynx

Accessory: Function

Controls shoulder and neck muscles, facilitating head movement. Motor fibers to trapezius and sternocleidomastoid muscles.

Hypoglossal: Function

Controls tongue movements for speech and swallowing.

Carry somatic motor fibers to intrinsic and extrinsic muscles of tongue, and proprioceptor fibers from same muscles to brain stem.

Olfactory: Origin/Course

Originates in the nasal cavity, travels through the cribriform plate of the ethmoid bone to the olfactory bulb.

Fibers of olfactory bulb neurons extend posteriorly as olfactory tract, which runs beneath frontal lobe to enter cerebral hemispheres and terminates in primary olfactory cortex.

Optic: Origin/Course

Originates in the retina, travels through the optic canal of the sphenoid bone to the optic chiasm, where some fibers cross over. The optic tract continues to the nucleus of the thalamus before projecting to the primary occipital cortex.

Occulomotor: Origin/Course

Originates in the ventral midbrain, travels through the bony orbit, via superior orbital fissure, to eye.

Trochlear: Origin/Course

Originates in the dorsal midbrain, and travels ventrally around midbrain to enter orbit through superior orbital fissure along with oculomotor nerves.

Trigeminal: Origin/Course

Ophthalmic: Fibers run from face to pons via superior orbital fissure.

Maxillary: Fibers run from face to pons via foramen rotundum.

Mandibular: Fibers pass through skull via foramen ovale.

Abducens: Origin/Course

Fibers leave inferior pons and enter orbit via superior orbital fissure to run to eye

Facial: Origin/Course

Fibers issue from pons, enter temporal bone via internal acoustic meatus, run within bone (through inner ear cavity) before emerging through stylomastoid foramen. Then to lateral aspect of face

Vestibulocochlear/Auditory: Origin/Course

Fibers arise from hearing/equilibrium apparatus within inner ear of temporal bone, through internal acoustic meatus to enter brain stem at pons-medulla border.

Afferent fibers from hearing receptors in cochlea form the cochlear division

Equilibrium receptors in semicircular canals and vestibule form the vestibular division

Glossopharyngeal: Origin/Course

Fibers emerge from medulla and leave skull via jugular foramen to run to throat

Vagus: Origin/Course

Fibers emerge from medulla, pass through skull via jugular foramen, and descend through neck region into thorax and abdomen

Accessory: Origin/Course

Rootlets arise laterally from superior region (C1-Cs) of spinal cord, pass upward along spinal cord, and enter the skull as the accessory nerves via foramen magnum. The accessory nerves exit from skull through jugular foramen together with the vagus nerves, and supply two large neck muscles.

Hypoglossal: Origin/Course

Fibers arise by a series of roots from medulla and exit from skull via hypoglossal canal to travel to tongue.

Olfactory: Deficiencies

Fracture of ethmoid bone or lesions of olfactory fibers may result in partial or total loss of smell, a condition known as anosmia

Optic: Deficiencies

Damage to optic nerve results in blindness in eye served by nerve. Damage to visual pathway beyond the optic chiasma results in partial visual losses. Visual defects are called anopsias

Occulomotor: Deficiencies

In oculomotor nerve paralysis, eye cannot be moved up, down, or inward. At rest, eye rotates laterally. Upper eyelid droops (ptosis), and the person has double vision and trouble focusing on close objects.

Trochlear: Deficiencies

Damage to a trochlear nerve results in double vision (diplopia) and impairs ability to rotate eye inferolaterally.

Trigeminal: Deficiencies

Trigeminal neuralgia caused by inflammation of trigeminal nerve, is widely considered to produce most excruciating pain known. The stabbing pain lasts for a few seconds to a minute, but it can be relentless, occurring a hundred times a day. Thought to be caused by a loop of artery or vein that compresses the trigeminal nerve near its exit from the brain stem. Several drugs are used to treat this frustrating condition. In severe cases, traditional or gamma knife surgery relieves the agony

Abducens: Deficiencies

In abducens nerve paralysis, eye cannot be moved laterally. At rest, eyeball rotates medially

Facial: Deficiencies

Bell's palsy is characterized by paralysis of facial muscles on affected side and partial loss of taste sensation. Caused by inflamed and swollen facial nerve, possibly due to herpes simplex 1 viral infection. Lower eyelid droops, corner of mouth sags, tears drip continuously from eye and eye cannot be completely closed (dry-eye syndrome may occur). Treated with corticosteroids. (70% recovery rate)

Vestibulocochlear: Deficiencies

Lesions of cochlear nerve or cochlear receptors result in central, or nerve, deafness. Damage to vestibular division produces dizziness, rapid involuntary eye movements, loss of balance, nausea, and vomiting.

Glossopharyngeal: Deficiencies

Injured or inflamed glossopharyngeal nerves impair swallowing and taste

Vagus: Deficiencies

vagal nerve paralysis can lead to hoarseness or loss of voice. Other symptoms are difficulty swallowing and impaired digestive system motility.

sympathetic nerves, which mobilize and accelerate vital body processes (and shut down digestion), would dominate.

Accessory: Deficiencies

Injury to one accessory nerve causes head to turn toward the injured side as a result of sternocleidomastoid muscle paralysis. Shrugging that shoulder becomes difficult

Hypoglossal: Deficiencies

Damage to hypoglossal nerves causes difficulties in speech and swallowing. If both nerves are impaired, the person cannot protrude tongue. If only one side is affected, tongue deviates toward affected side; eventually paralyzed side begins to atrophy.