I- Olfactory

II- Optic

III- Oculomotor

IV- Trochlear

V- Trigeminal

VI- Abducens

VII- Facial

VIII- Vestibulocochlear

IX- Glossopharyngeal

X- Vagus

XI- Accessory

XII- Hypoglossal

12 pairs primarily serving the head and neck; only one pair, the VAGUS NERVES, extends into the thoracic and abdominal cavities; all but first 2 (olfactory & optic) arise from the brain stem & pass through foramina in the base of the skull to reach their destination; most are mixed nerves; 3 pairs are strictly sensory in function (optic, olfactory & vestibulocochlear)

Origin & Course: Fibers arise from olfactory epithelium and run through cribriform plate of ethmoid bone to synapse in olfactory bulbs

Function: Purely sensory- carries afferent impulses associated with sense of smell.

Testing: Person is asked to sniff aromatic substances and identify.

Origin & Course: Fibers arise from retina of eye to form the optic nerve and pass through optic canal of orbit. Fibers partially cross over at the optic chiasma and continue on to the thalamus as the optic tracts. Final fibers of this pathway travel from the thalamus to the optic cortex as optic radiation.

Function: Purely sensory- carries afferent impulses associated with vision.

Testing: Vision & vision field are determined w/eye chart & by testing the point at which the person first sees an object (finger) moving into the visual plane. Fundus of eye viewed w/ opthalmoscope to detect papilledema (swelling of optic disc, or point at which optic nerve leaves the eye) and to observe the blood vessels.

Origin & Course: Fibers emerge from dorsal midbrain and course ventrally to enter the orbit. They exit from skull via superior orbital fissure.

Function: Primarily motor- somatic motor fibers to inferior oblique and superior, inferior, and medial rectus muscles, which direct eyeball, and to levator palpebrae muscles of the superior eyelid; parasympathetic fibers to iris and smooth muscle controlling lens shape (reflex responses to varying light intensity and focusing of eye for near vision). Sensory (proprioceptor) afferents, which run from same four extrinisc eye muscles to brain.

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

Origin & Course: Fibers emerge from midbrain and exit from skull via superior orbital fissure.

Function: Primarily motor- provides somatic motor fibers to superior oblique muscle (an extrinsic eye muscle).

Testing: Tested in common with cranial nerve III.

Origin & Course: Fibers emerge from pons and form three divisions, which exit separately from skull: mandibular division through foramen ovale in sphenoid bone, and opthalmic division through superior orbital fissure of eye socket.

Function: Mixed- major sensory nerve of face; conducts sensory impulses from skin of face and anterior scalp, from mucosae of mouth & nose, and from surface of eyes; mandibular division also contains motor fibers that innervate muscles of mastication and muscles of floor of mouth.

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

Origin & Course: Fibers leave inferior pons and exit from skull via superior orbital fissure to run to eye.

Function: Carries motor fibers to lateral rectus muscle of eye.

Testing: Tested in common with cranial nerve III.

Origin & Course: Fibers leave pons and travel through temporal bone via internal acoustic meatus, exiting via stylomastoid foramen to reach the face.

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

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

Origin & Course: Fibers run from inner-ear equilibrium and hearing apparatus, housed in temporal bone, through internal acoustic meatus to enter pons.

Function: Purely sensory- vestibular branch transmits impulses associated with sense of equilibrium from vestibular apparatus and semicircular canals; cochlear branc transmits impulses associated with hearing from cochlea.

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

Origin & Course: Fibers emerge from medulla and leave skull via jugular foramen to run to throat.

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

Testing: A tongue depressor is used to check the position of the uvula. Gag and swallowing reflexes are checked. Subject is asked to speak and cough. Posterior third of tongue may be tested for taste.

Origin & Course: Fibers emerge from medulla and pass through jugular foramen and descend through neck region into thorax and abdomen.

Function: Mixed- fibers carry somatic motor impulses to pharynx and larynx and sensory fibers from same structures; 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 craneal nerve IX (IX & X are tested in common since they both innervate muscles of throat and mouth).

Origin & Course: Fibers arise from medulla and superior aspect of spinal cord and travel through jugular foramen to reach muscles of neck and back.

Function: Mixed (but primarily motor in function)- provides somatic motor fibers to sternocleidomastoid and trapezius muscles and to muscles of soft palate, pharynx, and larynx (spinal and medullary fibers respectively)

Testing: Sternocleidomastoid and trapezius muscles are checked for strength by asking a person to rotate head and shoulders against resistence.

Origin & Course: Fibers arise from medulla and exit from skull via hypoglossal canal to travel to tongue.

Function: Mixed (but primarily motor in function)- carries somatic motor fibers to muscles of tongue.

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