I. Olfactory. These are the tiny sensory nerves (filaments) of smell, which run from the nasal mucosa to synapse with the olfactory bulbs.
Olfactory nerve fibers arise from olfactory receptor cells located in olfactory epithelium of nasal cavity and pass through cribriform plate of ethmoid bone to synapse in olfactory bulb.
II. Optic. Because this sensory nerve of vision develops as an outgrowth of the brain, it is really a brain tract.
Origin and course: Fibers arise from retina of eye to form optic nerve, which passes through optic canal of orbit. The optic nerves converge to form the optic chiasma where fibers partially cross over, continue on as optic tracts, enter thalamus, and synapse there. Thalamic fibers run (as the optic radi- ation) to occipital (visual) cortex, where visual interpretation occurs
III. Oculomotor. The name oculomotor means "eye mover." This nerve supplies four of the six extrinsic muscles that move the eyeball in the orbit.
Origin and course: Fibers extend from ventral midbrain (near its junction with pons) and pass through bony orbit, via superior orbital fissure, to eye.
The name trochlear means"pulley"and it innervates an extrinsic eye muscle that loops through a pulley-shaped ligament in the orbit.
Origin and course: Fibers emerge from dorsal midbrain and course ventrally around midbrain to enter orbit through superior orbital fissure along with oculomotor nerves.
V. Trigeminal. Three (tri) branches spring from this, the largest of the cranial nerves. It supplies sensory fibers to the face and motor fibers to the chewing muscles.
Largest of cranial nerves; fibers extend from pons to face, and form three divisions (trigemina threefold): ophthalmic, maxillary, and mandibular divisions. As major general sensory nerves of face, transmit afferent impulses from touch, temperature, and pain receptors. Cell bodies of sensory neurons of all three divisions are located in large trigeminal ganglion.
VI. Abducens. This nerve controls the extrinsic eye muscle that abducts the eyeball (turns it laterally).
Origin and course: Fibers leave inferior pons and enter orbit via superior orbital fissure to run to eye.
VII. Facial. A large nerve that innervates muscles of facial expression (among other things).
Origin and course: Fibers issue from pons, just lateral to abducens nerves (see Figure 13.5), enter temporal bone via internal acoustic meatus, and run within bone (and through inner ear cavity) before emerging through stylomastoid foramen; nerve then courses to lateral aspect of face.
VIII. Vestibulocochlear. This sensory nerve for hearing and balance was formerly called the auditory nerve.
Origin and course: Fibers arise from hearing and equilibrium apparatus located within inner ear of temporal bone and pass through internal acoustic meatus to enter brain stem at pons-medulla border. Afferent fibers from hearing receptors in cochlea form the cochlear division; those from equilibrium receptors in semicircular canals and vestibule form the vestibular division (ves- tibular nerve); the two divisions merge to form vestibulocochlear nerve
IX. Glossopharyngeal. The name glossopharyngeal means "tongue and pharynx," and reveals the structures that this nerve helps to innervate.
Origin and course: Fibers emerge from medulla and leave skull via jugular foramen to run to throat.
Function: Mixed nerves that innervate part of tongue and pharynx. Provide somatic motor fibers to, and carry proprioceptor fibers from, a superior pharyngeal muscle called the stylopharyngeus, which ele- vates the pharynx in swallowing. Provide parasympathetic motor fibers to parotid salivary glands (some of the nerve cell bodies of these parasympathetic motor neurons are located in otic ganglion).
This nerve's name means "wanderer" or "vagabond," and it is the only cranial nerve to extend beyond the head and neck to the thorax and abdomen.
Origin and course: The only cranial nerves to extend beyond head and neck region. Fibers emerge from medulla, pass through skull via jugular foramen, and descend through neck region into thorax and abdomen.
XI. Accessory. Considered an accessory part of the vagus nerve, this nerve was formerly called the spinal accessory nerve.
Origin and course: Unique in that they are formed from ventral rootlets that emerge from the spinal cord, not the brain stem. These rootlets arise from superior region (C1-C5) of spinal cord, pass upward along spinal cord, and enter the skull as the accessory nerves via fora- men magnum. The accessory nerves exit from skull through jugular foramen together with the vagus nerves, and supply two large neck muscles. Until recently, it was thought that the accessory nerves also received a contribution from cranial rootlets, but it has now been de- termined that in almost all people, these cranial rootlets are instead part of the vagus nerves. This raises an interesting question: Should the accessory nerves still be considered cranial nerves? Some anato- mists say "yes" because they pass through the cranium. Others say "no" because they don't arise from the brain. Stay tuned!
XII. Hypoglossal. The name hypoglossal means under the tongue. This nerve runs inferior to the tongue and innervates the tongue muscles.
Origin and course: As their name implies (hypo below; glossal tongue), hypoglossal nerves mainly serve the tongue. Fibers arise by a series of roots from medulla and exit from skull via hypoglossal canal to travel to tongue.