Cranial nerves are nerves that emerge directly from the brain, in contrast to spinal nerves which emerge from segments of the spinal cord. In humans, there are 12 pairs of cranial nerves. Only the first and the second pair emerge from the cerebrum; the remaining 10 pairs emerge from the brainstem.
Cranial nerves in non-human vertebrates
Human cranial nerves are nerves similar to those found in many other vertebrates. Cranial nerves XI and XII evolved in other species to amniotes (non-amphibian tetrapods) thus totaling twelve pairs. In some primitive cartilaginous fishes, such as the spiny dogfish or mud shark (Squalus acanthias), there is a terminal nerve numbered zero (as it exits the brain before the traditionally designated first cranial nerve).
List of cranial nerves
New research indicates CN0 may play a role in the detection of pheromones  Linked to olfactory system in human embryos
As the list is important to keep in mind during the examination of the nervous system, there are many mnemonic devices in circulation to help remember the names and order of the cranial nerves. Because the mind recalls rhymes well, the best mnemonics often use rhyming schemes. Three of the best known examples are, "On Old Olympus's Towering Tops, A Fine-Vested German Viewed Some Hops," "Oh, Oh, Oh To Take A Family Vacation! Go Vegas After Hours!", and "Oh, Oh, Oh, To Touch And Feel, A Good Velvet, Ahh, Heaven." A useful mnemonic for remembering which nerves are motor (M), sensory (S), or both (B) is, "Some Say Money Matters But My Brother Says Big Brains Matter Most". There are many more mnemonics from many sources, for example OLd OPie OCcasionally TRies TRIGonometry And Feels VEry GLOomy, VAGUe, And HYPOactive.
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