Cranial nerve
| Nerve: Cranial nerves | |
|---|---|
 | |
| Inferior view of the brain and brain stem showing the cranial nerves (with the exception of nerve 0). An unlabelled version is here. | |
| Latin | nervus cranialis (plural: nervi craniales) |
| Code | TA A14.2.00.038 |
Cranial nerves are nerves that emerge directly from the brain, in contrast to spinal nerves, which emerge from segments of the spinal cord. In humans, there are traditionally twelve pairs of cranial nerves (although an additional anterior pair of nerves, numbered 0, also exists). The first three pairs (including nerve 0) emerge from the cerebrum; the remaining ten pairs emerge from the brainstem.
The cranial nerves are part of the peripheral nervous system (PNS), with the exception of cranial nerve II (the optic nerve), which is not a true peripheral nerve but a tract of the diencephalon leading to the retina; both the optic nerve and the retina are hence part of the central nervous system (CNS).[1] The axons of the remaining twelve nerves extend beyond the brain and are therefore considered part of the PNS.[2] The ganglia of the cranial nerves originate in the CNS.
Cranial nerves in non-human vertebrates
Other amniotes (non-amphibian tetrapods) have cranial nerves similar to those of humans. In anamniotes (fishes and amphibians), in contrast, cranial nerves XI and XII do not exist as such, nerve XI being an integral part of nerve X and nerve XII being represented by a variable number of spinal nerves emerging from vertebral segments fused into the occiput; nerves XI and XII only became discrete nerves in the ancestors of amniotes (non-amphibian tetrapods).
List of cranial nerves
| Number | Name | Sensory, motor, or both | Origin/Target | Nuclei | Function |
| 0 | Terminal | Purely sensory | Lamina terminalis | Septal nuclei | Involved in the detection of pheromones.[3] |
| I | Olfactory | Purely sensory | Telencephalon | Anterior olfactory nucleus | Transmits the sense of smell from the nasal cavity.[4] Located in the olfactory foramina in the cribriform plate of the ethmoid bone. |
| II | Optic | Sensory | Retinal ganglion cells | Lateral geniculate nucleus[5] | Transmits visual signals from the retina of the eye to the brain.[6] Located in the optic canal. |
| III | Oculomotor | Mainly motor | Anterior aspect of Midbrain | Oculomotor nucleus, Edinger-Westphal nucleus | Innervates the levator palpebrae superioris, superior rectus, medial rectus, inferior rectus, and inferior oblique, which collectively perform most eye movements. Also innervates the sphincter pupillae and the muscles of the ciliary body. Located in the superior orbital fissure. |
| IV | Trochlear | motor | Dorsal aspect of Midbrain | Trochlear nucleus | Innervates the superior oblique muscle, which depresses, rotates laterally, and intorts the eyeball. Located in the superior orbital fissure. |
| V | Trigeminal | Both sensory and motor | Pons | Principal sensory trigeminal nucleus, Spinal trigeminal nucleus, Mesencephalic trigeminal nucleus, Trigeminal motor nucleus | Receives sensation from the face and innervates the muscles of mastication. Located in the superior orbital fissure (ophthalmic nerve - V1), foramen rotundum (maxillary nerve - V2), and foramen ovale (mandibular nerve - V3). |
| VI | Abducens | Mainly motor | Nuclei lying under the floor of the fourth ventricle Pons | Abducens nucleus | Innervates the lateral rectus, which abducts the eye. Located in the superior orbital fissure. |
| VII | Facial | Both sensory and motor | Pons (cerebellopontine angle) above olive | Facial nucleus, Solitary nucleus, Superior salivary nucleus | Provides motor innervation to the muscles of facial expression, posterior belly of the digastric muscle, stylohyoid muscle, and stapedius muscle. Also receives the special sense of taste from the anterior 2/3 of the tongue and provides secretomotor innervation to the salivary glands (except parotid) and the lacrimal gland. Located in and runs through the internal acoustic canal to the facial canal and exits at the stylomastoid foramen. |
| VIII | Vestibulocochlear (also known as the auditory-vestibular or acoustic nerve) | Mostly sensory | Lateral to CN VII (cerebellopontine angle) | Vestibular nuclei, Cochlear nuclei | Senses sound, rotation, and gravity (essential for balance and movement). More specifically, the vestibular branch carries impulses for equilibrium and the cochlear branch carries impulses for hearing. Located in the internal acoustic canal. |
| IX | Glossopharyngeal | Both sensory and motor | Medulla | Nucleus ambiguus, Inferior salivary nucleus, Solitary nucleus | Receives taste from the posterior 1/3 of the tongue, provides secretomotor innervation to the parotid gland, and provides motor innervation to the stylopharyngeus. Some sensation is also relayed to the brain from the palatine tonsils. Located in the jugular foramen. |
| X | Vagus | Both sensory and motor | Posterolateral sulcus of Medulla | Nucleus ambiguus, Dorsal motor vagal nucleus, Solitary nucleus | Supplies branchiomotor innervation to most laryngeal and pharyngeal muscles (except the stylopharyngeus, which is innervated by the glossopharyngeal). Also provides parasympathetic fibers to nearly all thoracic and abdominal viscera down to the splenic flexure. Receives the special sense of taste from the epiglottis. A major function: controls muscles for voice and resonance and the soft palate. Symptoms of damage: dysphagia (swallowing problems), velopharyngeal insufficiency. Located in the jugular foramen. |
| XI | Accessory (often separated into the cranial accessory and spinal accessory nerves) | Mainly motor | Cranial and Spinal Roots | Nucleus ambiguus, Spinal accessory nucleus | Controls the sternocleidomastoid and trapezius muscles, and overlaps with functions of the vagus nerve (CN X). Symptoms of damage: inability to shrug, weak head movement. Located in the jugular foramen. |
| XII | Hypoglossal | Mainly motor | Medulla | Hypoglossal nucleus | Provides motor innervation to the muscles of the tongue (except for the palatoglossus, which is innervated by the vagus nerve) and other glossal muscles. Important for swallowing (bolus formation) and speech articulation. Located in the hypoglossal canal. |
Mnemonic devices
There are many mnemonic devices in circulation to help remember the names and order of the cranial nerves. Because the mind recalls rhymes well, the best mnemonics often use rhyming schemes.
An example mnemonic sentence for the initial letters "OOOTTAFAGVSH" is "On old Olympus's towering tops, a Finn and German viewed some hops,"[7] and for the initial letters "OOOTTAFVGVAH" is "Oh, oh, oh, to touch and feel very good velvet...ah, heaven."[8] The differences between these depend on "acoustic" versus "vestibulocochlear" and "spinal-accessory" versus "accessory".
A useful mnemonic for remembering which nerves are motor (M), sensory (S), or both (B) is, "Some Say Marry Money But My Brother Says Big Brains Matter More". There are many more mnemonics from many sources, for example OLd OPie OCcasionally TRies TRIGonometry And Feels VEry GLOomy, VAGUe, And HYPOactive.[9]
See also
References
- ↑ Board Review Series – Neuroanatomy, Fourth Edition, Lippincott Williams & Wilkins, Maryland 2008, p. 177. ISBN 978-0-7817-7245-7.
- ↑ James S. White (21 March 2008). Neuroscience. McGraw-Hill Professional. pp. 1–. ISBN 978-0-07-149623-0. Retrieved 17 November 2010.
- ↑ R. Douglas Fields, Sex and the Secret Nerve, February/March 2007; Scientific American Mind
- ↑ McCracken, Thomas (2000). New Atlas of Human Anatomy. China: MetroBooks. pp. 1–240. ISBN 1-5866-3097-0.
- ↑ Henry Gray (1821–1865). Anatomy of the Human Body. 1918.
- ↑ McCracken, Thomass (2000). New Atlas of Human Anatomy. China: MetroBooks. pp. 1–240. ISBN 1-5866-3097-0.
- ↑ Dennis Long (2006). Vive Les Verbes Français!: 6,000 Verbs to Add Savoir-Flair to Your French. McGraw-Hill Professional. p. 8. ISBN 9780071478755.
- ↑ Kevin C. Wang, Rita A. Mukhtar, and Rodrigo E Saenz (2005). Hardcore Neuroscience. Lippincott Williams & Wilkins. p. 23. ISBN 9781405104715.
- ↑ Saladin, Kenneth S. (2008). Human anatomy (2nd ed.). McGraw-Hill Higher Education. ISBN 0071102094.
Additional images
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3D rendering of cranial nerves (inferior view).
External links
Animations of cranial nerve input to extraocular muscles can be found here (University of Liverpool Veterinary School).
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