cranial nerves

Cranial nerves:

There are twelve cranial nerves, ten of which originate from the brain stem. All cranial nerves are either mixed or sensory. Once, it was believed that the third, fourth, sixth, eleventh and twelfth were entirely motor tracts

The first cranial nerve is the olfactory tract. The olfactory tract is a purely sensory tract for smell

The second cranial nerve is the optic nerve, a sensory nerve for vision. The optic nerve arises from the retina and forms the optic chiasma, where the tracts cross one another

The third cranial nerve is the oculomotor, a mixed nerve. The oculomotor nerve controls movement of the eyelid and eye, accommodation of the lens for near vision and constriction of the pupil. The sensory function of the oculomotor nerves is proprioception (muscle sense) of the optic muscles

The fourth cranial nerve is the trochlear nerve. The trochlear nerve is mainly motor for the movement of the oblique external (trochlear) muscle of the eye, but also serves as a muscle sense nerve

The fifth cranial nerve is the trigeminal nerve, the largest of the cranial nerves. The trigeminal nerve serves a motor function in controlling chewing. The trigeminal splits into three areas for sensory purposes:

maxillary, containing sensory fibers for the mucosa of the nose, palate, sections of the pharynx, upper lip and teeth, lower eyelid and cheek
mandibular, containing sensory fibers for the anterior two thirds of the tongue, lower teeth, sides of the head in front of the ear and the skin over the mandible
ophthalmic, containing sensory fibers for the skin of the upper eyelid, nasal cavity, lacrimal glands, eye, forehead, and the anterior half of the scalp

The sixth cranial nerve is the abducens nerve, primarily a motor nerve. The abducens nerve serves to control the lateral muscles of the eye and proprioception in the lateral rectus muscles, rolling the eye laterally

The seventh cranial nerve is the facial nerve. The facial nerve's motor function controls the facial, scalp, neck muscles, parasympathetic distribution to the lacrimal, submandibular, nasal, sublingual, and palatine glands. Sensory input to the facial nerve comes from taste buds on the posterior one third of the tongue and proprioceptors in the scalp and face

The eighth cranial nerve is the vestibulocochlear nerve. The vestibulocochlear nerve has two branches. The cochlear branch is concerned with hearing. The vestibular, with equilibrium

The ninth cranial nerve is the glossopharengeal nerve. The glossopharengeal nerve controls the muscles involved in swallowing and the secretion of saliva. It also is involved in taste, the regulation of blood pressure and proprioception

The tenth cranial nerve is the vagus nerve. This is the only nerve to extend to the abdominal cavity. The motor portion helps control the respiratory passageways, heart, lungs, stomach, small intestine, esophagus and gallbladder. Sensory impulses are sent through the vagus from the internal organs and some abdominal muscles

The eleventh cranial nerve is the accessory nerve. The accessory nerve helps control swallowing, head movement, and sensory purposes in the muscles

The twelfth cranial nerve is the hypoglossal nerve. The hypoglossal nerve controls the tongue during speech and for proprioceptic purposes