There are twelve cranial nerves in total. The olfactory nerve (CN I) and optic nerve (CN II) originate from the cerebrum.
Cranial nerves III – XII arise from the brain stem (Figure 1). They can arise from a specific part of the brain stem (midbrain, pons or medulla), or from a junction between two parts:
Midbrain – the trochlear nerve (IV) comes from the posterior side of the midbrain. It has the longest intracranial length of all the cranial nerves.
Midbrain-pontine junction – oculomotor (III).
Pons – trigeminal (V).
Pontine-medulla junction – abducens, facial, vestibulocochlear (VI-VIII).
Medulla Oblongata – posterior to the olive: glossopharyngeal, vagus, accessory (IX-XI). Anterior to the olive: hypoglossal (XII).
The cranial nerves are numbered by their loca