A cranial nerve is any nerve which is attached directly to the brain or brainstem. This is different from spinal nerves which are attached to segments of the spinal cord. Cranial nerves relay information more directly between the brain and body (mostly parts of the head and neck).
Each cranial nerve exists as a pair and is present on both sides of the central nervous system. All cranial nerves appear above the first vertebra in the neck (cervical vertebra).
In humans there are twelve cranial nerves pairs. They are numbered using Roman numerals I–XII based on their order from the front of the brain to the back, where the brainstem is.