Cranial Nerves - The Twelve Pairs
Cranial nerves emerge directly from the brain, unlike spinal nerves that are connected to different segments of the spinal cord. There are 12 pairs of cranial nerves, 10 of 12 emerge directly from the brain stem. The nerves function is relay information bewteen different parts of the body and the brain, predominantly to areas of the head and neck.
The cranial nerves are connected to the central nervous system, the nerves are paired and are present of both sides of the brain. It is commonly stated there are 12 to 13 cranial nerve pairs, in medical annotation they are assigned Roman numerals from I-XII. The numbering is in order in which they appear in the brain from front to back.
Ten pairs emerge from the brainstem whereas the first two pairs, cranial nerve pairs (I) the olfactory nerves and (II) the optic nerves arise from the cerebum and forebrain respectively.
Generally, cranial nerves are described as being components of the peripheral nervous system (PNS), however on a structural level the olfactory, optic an terminal nerves are more concisely considered to be part of the central nervous system (CNS).
Most typically, humans are considered to have twelve pairs of cranial nerves (I–XII). They are: the olfactory nerve (CN I), the optic nerve (CN II), oculomotor nerve (CN III), trochlear nerve (CN IV), trigeminal nerve (CN V), abducens nerve (CN VI), facial nerve (CN VII), vestibulocochlear nerve (CN VIII), glossopharyngeal nerve (CN IX), vagus nerve (CN X), accessory nerve (CN XI), and hypoglossal nerve (CN XII).