Cranial nerves are the nerves that emerge directly from the brain [including the brainstem], in contrast to spinal nerves [which emerge from segments of the spinal cord]. Ten of the cranial nerves originate in the brainstem. Cranial nerves relay information between the brain and
parts of the body, primarily to and from regions of the head and neck. Spinal nerves emerge sequentially from the spinal cord with the spinal nerve closest to the head [C1] emerging in the space above the first cervical vertebra. The cranial nerves, however, emerge from the central nervous system above this level. Each cranial nerve is paired and is present on both sides. In humans there are twelve cranial nerves pairs, which are assigned Roman numerals I–XII. The numbering of the cranial
nerves is based on the order in which they emerge from the brain, front to back [brainstem].Cranial Nerves
Above: Lateral view of the brain stem showing the locations of the cranial nerves III - XII.
The, olfactory nerves [I] and optic nerves [II] emerge from the cerebrum or forebrain, and the remaining ten pairs arise from the brainstem, which is the lower part of the brain.
Above: Inferior view of the brain with the pairs of cranial nerves labeled.
The cranial nerves are considered components of the peripheral nervous system [PNS], although on a structural level the olfactory [I], optic [II], and trigeminal [V] nerves are more accurately considered part of the central nervous system [CNS].
Humans are considered to have twelve pairs of cranial nerves [I–XII]. They are: the olfactory nerve [I], the optic nerve [II], oculomotor nerve [III], trochlear nerve [IV], trigeminal nerve [V], abducens nerve [VI], facial nerve [VII], vestibulocochlear nerve [VIII], glossopharyngeal nerve [IX], vagus nerve [X], accessory nerve [XI], and hypoglossal nerve [XII].
C.N. I | olfactory nerve | olfactory foramina [cribriform plate of the ethmoid bone] | special sensory | olfaction [smell] - olfactory epithelium |
C.N. II | optic nerve | optic canals | special sensory | retina of the eye [sight] |
C.N. III | oculomotor nerve | superior orbital fissure | motor | inferior oblique, medial rectus, superior rectus, and inferior recuts muscles of the eye |
C.N. IV | trochlear nerve | superior orbital fissure | motor | superior oblique muscle of the eye |
C.N. V | trigeminal nerve | |||
C.N. V, branch 1: ophthalmic nerve | superior orbital fissure, supraorbital foramen | sensory | skin on the upper third of the face | |
C.N. V, branch 2: maxillary nerve | foramen rotundum, infraorbital foramen | sensory | skin on the middle third of the face | |
C.N. V, branch 3: mandibular nerve | foramen ovale, mandibular foramen, mental foramen | sensory | skin on the lower third of the face, pain from the tongue | |
C.N. VI | abducens nerve | superior orbital fissure | motor | lateral recuts muscle of the eye |
C.N. VII | facial nerve | internal acoustic meatus, stylomastoid foramen | motor, special sensory | motor: muscles of facial expression special sensory: taste buds on the anterior two-thirds of the tongue |
C.N. VIII | vestibulocochlear nerve | internal acoustic meatus | special sensory | auditory [hearing], balance, and equilibrium - inner ear [cochlear and vestibular apparatus] |
C.N. IX | glossopharyngeal nerve | jugular foramen | motor, special sensory | motor: pharynx muscles special sensory: taste buds on the posterior third of the tongue |
C.N. X | vagus nerve | jugular foramen | motor, sensory, special sensory | motor: heart, smooth muscle of pharynx and organs of the gut sensory: skin across the throat and the external acoustic meatus special sensory: taste, gag reflex |
C.N. XI | accessory nerve | jugular foramen, foramen magnum | motor | trapezius, sternocleidomastoid, muscles of the pharynx |
C.N. XII | hypoglossal nerve | hypoglossal canal | motor | muscles of the tongue |
Mnemonic phrases can be helpful to remember the order of the cranial nerves. Here are two popular mnemonics for the order of the cranial nerves [I-XII]:
- Oh Once One Takes The Anatomy Final, Very Good Vacations Are Heavenly
- Oh, Oh, Oh, To Touch And Feel Very Good Velvet, A-H
The cranial nerves carry motor, sensory, and/or special sensory signals. Motor signals innervate muscles/tissues, sensory signals send information to the CNS from sensory receptors, and special sensory signals send information to the CNS from the special senses [vision, hearing and balance, and taste]. Some cranial nerves carry more than one type of signal; one cranial nerve even carries all three types of signals.
To enter/exit the skull, cranial nerves pass through openings in the base of the skull.
Above: Diagram showing how the cranial nerves enter/exit the cranial cavity through the skull.
Above: Image of cadaver with the left cranial nerves labeled.
Attributions
- "Anatomy 204L: Laboratory Manual [Second Edition]" by Ethan Snow, University of North Dakota is licensed under CC BY-NC 4.0
- "Anatomy and Physiology I Lab" by Victoria Vidal is licensed under CC BY 4.0
- "Brain human normal inferior view.svg" by Patrick J. Lynch, medical illustrator is licensed under CC BY 2.5