Cranial nerves contain sensory and motor neuron pathways that connect directly to the brain. Twelve pairs of cranial nerves pass through the openings in the skull to innervate regions of the head and neck. One of the pairs, the vagus nerves, also extend caudally to innervate respiratory system bronchi and digestive system organs including the stomach and intestines.

In embryological descending order, the twelve cranial nerves, always designated by Roman numerals, are:

• I. Olfactory
• II. Optic
• III. Oculomotor
• IV. Trochlear
• V. Trigeminal
• VI. Abducens
• VII. Facial
• VIII. Auditory (also termed the Vestibulocochlear)
• IX. Glossopharyngeal
• X. Vagus
• XI. Spinal Accessory
• XII. Hypoglossal.

There is a classic mnemonic (a saying where the first letter of each word stands for each of the cranial nerves) used to remember the twelve cranial nerves: "On Old Olympus Towering Tops A Finn And German Viewed Some Hops."

In addition to purely sensory...