 Introduction/Background The human body has 12 paired cranial nerves (CNs) that provide specialized sensory and motor innervation to the head and neck region. As a group, the CNs have both sensory and motor components similar to those of the spinal nerves. Individually the CNs may be purely sensory, purely motor, or a mixture of both sensory and motor. Functions of the CNs may be divided into three sensory and three motor categories. The sensory group includes visceral sensory, which supplies sensory input from the internal organs; general sensory, which supplies tactile, pain, temperature, and other sensations; and special sensory, which includes the special senses of smell, vision, taste, hearing, and balance. Of the three motor functions, somatic motor nerves innervate muscles that develop from the body somites; branchial motor nerves innervate muscles derived from the branchial arches; and visceral motor nerves innervate the viscera, glands, and smooth muscle [1-4]. The CNs emerge in an orderly fashion from the rostral portion of the embryologically developing neural tube, which develops to form the brain. Anatomically, the 12 pairs of CNs are designated by numbers I-XII. The CNs include the olfactory (CN I), optic (CN II), oculomotor (CN III), trochlear (CN IV), trigeminal (CN V), abducens (CN VI), facial (CN VII), vestibulocochlear (CN VIII), glossopharyngeal (CN IX), vagus (CN X), spinal accessory (CN XI), and hypoglossal (CN XII) nerves. The olfactory (CN I) and optic (CN II) nerves are actually tracts formed from the telencephalon and diencephalon, respectively, and are not considered true nerves [4,5]. The CN nuclei arise in the brainstem, largely topologically arranged between the midbrain and the rostral cervical spine (CN XI). Current knowledge of CN anatomy has been improved by modern microsurgical techniques and endoscopic dissections, allowing visualization of the CN brainstem exit zones [3,4,6-13].
Cranial Neuropathy.  Introduction/Background The human body has 12 paired cranial nerves (CNs) that provide specialized sensory and motor innervation to the head and neck region. As a group, the CNs have both sensory and motor components similar to those of the spinal nerves. Individually the CNs may be purely sensory, purely motor, or a mixture of both sensory and motor. Functions of the CNs may be divided into three sensory and three motor categories. The sensory group includes visceral sensory, which supplies sensory input from the internal organs; general sensory, which supplies tactile, pain, temperature, and other sensations; and special sensory, which includes the special senses of smell, vision, taste, hearing, and balance. Of the three motor functions, somatic motor nerves innervate muscles that develop from the body somites; branchial motor nerves innervate muscles derived from the branchial arches; and visceral motor nerves innervate the viscera, glands, and smooth muscle [1-4]. The CNs emerge in an orderly fashion from the rostral portion of the embryologically developing neural tube, which develops to form the brain. Anatomically, the 12 pairs of CNs are designated by numbers I-XII. The CNs include the olfactory (CN I), optic (CN II), oculomotor (CN III), trochlear (CN IV), trigeminal (CN V), abducens (CN VI), facial (CN VII), vestibulocochlear (CN VIII), glossopharyngeal (CN IX), vagus (CN X), spinal accessory (CN XI), and hypoglossal (CN XII) nerves. The olfactory (CN I) and optic (CN II) nerves are actually tracts formed from the telencephalon and diencephalon, respectively, and are not considered true nerves [4,5]. The CN nuclei arise in the brainstem, largely topologically arranged between the midbrain and the rostral cervical spine (CN XI). Current knowledge of CN anatomy has been improved by modern microsurgical techniques and endoscopic dissections, allowing visualization of the CN brainstem exit zones [3,4,6-13].