The Cranial Nerves

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I. Olfactory

Function: Purely sensory- Carries impulses for sense of smell

Testing: Person is asked to sniff and identify aromatic substances, such as oil or cloves and vanilla


II. Optic

Function: Purely sensory- Carries impulses for vision

Testing: Vision and visual fields are determined with eye chart and by testing the point at which the person first sees the object (finger) moving into the visual field. Eye interior viewed with ophthalmoscope to detect swelling of optic disc (point which optic nerve leaves the eye) and to observe blood vessels


III. Oculomotor

Function: Mixed- motor fibers to inferior oblique and superior,inferior, and medial rectus muscles, which direct eyeball; to levator palpebrae muscles of eyelids; to iris and smooth muscle controlling lens shape and pupil size

Testing: Pupils are examined for size, shape, and equality. Pupillary reflex is tested with penlight (pupils should constrict when illuminated). Convergence for near vision is tested, as is subject's ability to follow objects up, down, side to side, and diagonally with eyes


IV. Trochlear

Function: Mixed- provides motor fibers to superior oblique muscle (an extrinsic eye muscle)

Testing: Tested in common with cranial nerve III


V. Trigeninal

Function: Mixed-conducts sensory impulses from skin of face and anterior scalp, from mucosae of mouth and nose; also contains motor fibers that activate the chewing muscles

Testing: Sensations of pain, touch, and temperature are tested with safety pin and hot and cold objects. Corneal reflex tested with wisp of cotton. Motor branch assessed by asking person to clench his teeth, open mouth against resistance, and move jaw side to side


VI. Abducens

Function: Carries motor fibers to lateral rectus muscle of eye

Testing: tested in common with cranial nerve III.


VII. Facial

Function: Mixed- supplies motor fibers to muscles of facial expression and to lacrimal and salivary glands; carries sensory fibers from taste receptors of anterior tongue

Testing: Anterior two-thirds of tongue is tested for ability to taste sweet (sugar), salty, sour (vinegar), and bitter (quinine) substances. Symmetry of face is checked. Subject is asked to close eyes, smile, whistle, and so on. Tearing is assessed with ammonia fumes


VIII. Vestibulocochlear

Function: Purely sensory- transmits impulses for senses of equilibrium and hearing

Testing: Hearing is checked by air and bone conduction using tuning fork


IX. Glossopharyngeal

Function: Mixed- motor fibers serve pharyngeal muscles and salivary glands; sensory fibers carry impulses from pharynx, posterior tongue (taste buds), and pressure receptors of carotid artery

Testing: Gag and swallowing reflexes are checked.subject is asked to speak and cough. Posterior third of tongue may be tested for taste.


X. Vagus

Function: Mixed- motor fibers to pharynx and larynx and sensory fibers from same structures; a very large portion is composed of parasympathetic motor fibers, which supply heart and smooth muscles of abdominal visceral organs; transmits sensory impulses from viscera

Testing: As for cranial nerve IX (IX and X are tested in common, since they both serve muscles of the throat and mouth.)


XI. Accessory

Function: Mixed- provides motor fibers to sternocleidomastoid and trapezius muscles

Testing: Sternocleidomastoid and trapezius muscles are checked for strength by asking person to rotate head and elevate shoulders against resistance


XII. Hypoglossal

Function: mixed- motor fibers serve muscles of tongue and sensory fibers carry impulses from tongue.

Testing: Person is asked to protrude and retract tongue. Any deviations in position are noted


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