Synonyms in the broadest sense
cranial nerve, cranial nerve, cranial nerves, optic nerve, olfactory nerve, oculomotor nerve, trochlear nerve, trigeminal nerve, facial nerve, abducens nerve, vestibulocochlear nerve, glossopharyngeal nerve, vagus nerve
Definition
The generic term cranial nerves (Nervi craniales) refers to 12 specific nerves of outstanding importance on each half of the body. For practical reasons, these are usually abbreviated with Roman numerals, i.e. from I (1) to XII (12). All but one of them (the 11th cranial nerve, Nervus accessorius) have in common that they either originate from the brain and leave it or enter it directly.
By definition, cranial nerves are actually so-called “peripheral nerves”, i.e. comparable, for example, to nerves that exit the spinal cord and supply our arms (body nerves). Ultimately, however, there are also deviations (e.g. in the 2nd cranial nerve, optic nerve), which are mainly due to the fact that the meninges are grouped differently around the actual nerve fibers of the nerve. Incidentally, the medical term for a normal peripheral nerve (e.g. a cranial nerve) always refers to a large number of nerve fibers, including special connective tissue, and not the axon of a single nerve cell (neuron).
The finished nerves and their nerve branches then partially follow a very characteristic course in the skull or on the outside of the skull, in certain connective tissue spaces, or even on the neck, which is described in more detail for the individual nerves. Of course, the attending physician does not only have to consider this course during surgical interventions, but also systematically examines the cranial nerves as part of a typical neurological examination. The order 1-12 of the cranial nerves reflects for most cranial nerves the height of the location of their core areas (nuclei) in the brain stem (this assignment does not apply to the 1st, 2nd and 11th cranial nerves due to certain special features, see there).
For example, the nerve cells which in their entirety make up the nucleus of the 4th cranial nerve are located higher up (cranially) in the brain stem than the nerve cells which bundle together to form the 12th cranial nerve. Each cranial nerve is formally assigned 1-4 core areas in the brain, smaller nerves such as the 4th cranial nerve originate/emerge from/into only one core area, larger nerves such as the 5th cranial nerve originate/into 4 cores! It is also possible that a single core shares fibers with several cranial nerves: The nucleus responsible for our sensitivity in the head area (Nucleus spinalis trigeminalis) contains influxes from 3 cranial nerves, namely V, IX and X.
