A
cranial nerve nucleus is a collection of
neurons (
gray matter) in the
brain stem that is associated with one or more
cranial nerves.
Axons carrying information to and from the cranial nerves form a
synapse first at these
nuclei. Lesions occurring at these nuclei can lead to effects resembling those seen by the severing of nerve(s) they are associated with. All the nuclei except that of the
trochlear nerve (CN IV) supply nerves of the same side of the body.