The Cranial Nerves

 

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Cranial Nerve

Composition

Function

Origin

Effect of Damage

Clinical Test

I Olfactory Nerve

Sensory

Smell

Olfactory mucosa in nasal cavity

Impaired sense of smell

Use an aromatic substance

II Optic Nerve

Sensory

Vision

Retina

Blindness in part of all of the visual field

Inspect retina with ophthalmoscope, test peripheral vision and visual acuity

III Oculomotor Nerve

Predominantly

motor

Eye movements

Midbrain

Drooping eyelid; dilated pupil; inability to move eye in some directions; double vision

Look for differences in size and shape of right and left pupils; test pupillary response to light; test ability to track moving objects

IV Trochlear Nerve

Predominantly

motor

Eye Movements

Midbrain

Double vision and inability to rotate eye inferolaterally

Test ability of eye to rotate inferolaterally

V Trigeminal Nerve - largest nerve, has three divisions

Sensory

Mixed

Touch, temperature, and pain sensations from upper face, mastication

Superior, middle, and inferior region of the face

Loss of sensation from upper and middle face; impaired chewing

Test corneal reflex; test sense of touch, pain and temperature with light touch, pinpricks, hot and cold objects; assess motor functions by palpating while subject clenches teeth

VI Abducens Nerve

Predominantly

motor

Lateral eye movement

Inferior pons

Inability to turn eye laterally

Test lateral eye movement

VII Facial Nerve

Mixed

Sensory - taste

Motor - facial expression, secretion of tears, salvia, nasal & oral mucus

Sensory: taste buds of anterior two-thirds of tongue

Motor: Pons

Inability to control facial muscles; sagging due to loss of muscle tone; distorted sense of taste, especially for sweets

Test tongue with substances - sugar, salt, vinegar

Test response of tear glands

Test ability to smile, frown, whistle, raise eyebrows

VIII Vestibulocochlear Nerve

Predominantly

sensory

Hearing and equilibrium

Sensor: Cochlea, vestibule & semicircular ducts of inner ear

Motor: Pons

Nerve deafness, dizziness, nausea, loss of balance and nystagmus

Look for nystagmus

Test hearing, balance and ability to walk a straight line

IX Glossopharyngeal Nerve

Mixed

Sensory: taste, tough, pressure, pain & temperature sensations from tongue & other ear

Motor: salivation, swallowing, gagging

Sensory: pharynx, middle and outer ear

Motor: medulla oblongata

Loss of bitter and sour taste, impaired swallowing

Test gag reflex, swallowing, and coughing

Test tongue with bitter and sour substances

X Vagus Nerve

Mixed

Sensory: taste, sensations of hunger, fullness & GI discomfort

Motor: swallowing, speech, deceleration of heart, bronchoconstriction

Sensory: thoracic & abdominal viscera, root of tongue, pharynx, larynx, etc

Motor: medulla oblongata

Hoarseness or loss of voice

Impaired swallowing and GI motility

 

Examine palatal movements during speech

Check for abnormalities of swallowing, absence of gag reflex, weak hoarse voice, inability to cough forcefully

XI Accessory Nerve

Predominantly

motor

Swallowing, head, neck, and shoulder movements

Medulla oblongata and spinal cord segments C1 to C6

Impaired movement of head, neck & shoulders; difficult shrugging shoulder on damaged side; paralysis of sternocleidomastoid

Test ability to rotate head and shrug shoulders against resistance

XII Hypoglossal Nerve

Predominantly

motor

Tongue movements of speech, food manipulation and swallowing

Medulla oblongata

Impaired speech and swallowing; inability to protrude tongue; deviation of tongue toward injured side

Note deviations of tongue

Test ability to protrude tongue against resistance