The twelve cranial nerves innervate the muscles and skin of the head, neck, and, in the case of the vagus, sacral, and |spinal accessory nerves|, many other important structures throughout the body. These ~nerves~ originate in the |pons|, the forebrain, |medulla| oblongata, and the uppermost part of the |spinal cord|, between the first few |cervical vertebrae|. The first four include the olfactory (1st), which innervates the nasal mucous layer and allows the sense of smell, the optic (2nd) which innervates the |retina| and allows the sense of sight, the oculomotor (3rd) which innervates the |pupil| and |cilia| of the |eye|, and the trochlear (4th) which innervates the superior oblique |eye| muscles. The next cranial ~nerve~ is the trigeminal (5th) which has three divisions: the ophthalmic (eye), maxillary (upper palate and face), and mandibular (jawbone, |tongue|, and auriculotemporal region). The sixth, seventh, and eigth ~nerves~ are the abducens (lateral rectus of |eye|), the facial (face and |ear| muscles), and the acoustic (outer and inner |ear| structures), respectively. The ninth cranial ~nerve~ is the glossopharyngeal, which innervates the |pharynx|, |tongue|, and tympanus of the |ear|. The tenth cranial ~nerve~, the vagus, has many branches which innervate a number of important structures, including the |heart|, |lungs|, and |stomach|. The eleventh cranial ~nerve~ is the accessory spinal ~nerve~, which innervates structures of the neck and throat, including the |pharynx| and the cervical ~lymph~ |glands|. The twelfth cranial ~nerve~ is the hypoglossal ~nerve~, which innervates the |tongue|.
