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Cranial Nerves
CN 0 - Cranial nerve zero
CN I - Olfactory
CN II - Optic
CN III - Oculomotor
CN IV - Trochlear
CN V - Trigeminal
CN VI - Abducens
CN VII - Facial
CN VIII - Vestibulocochlear
CN IX - Glossopharyngeal
CN X - Vagus
CN XI - Accessory
CN XII - Hypoglossal

Cranial nerves are nerves that emerge directly from the brain in contrast to spinal nerves which emerge from segments of the spinal cord. Although thirteen cranial nerves in humans fit this description, twelve are conventionally recognized. The nerves from the third onward arise from the brain stem. Except for the tenth and the eleventh nerve, they primarily serve the motor and sensory systems of the head and neck region. However, unlike peripheral nerves which are separated to achieve segmental innervation, cranial nerves are divided to serve one or a few specific functions in wider anatomical territories.

Names of Nerves

The 12 pairs of cranial nerves are traditionally abbreviated by the corresponding Roman numerals. They are numbered according to where their nuclei lie in the brain stem, e.g. Cranial Nerve III (the Oculomotor nerve) leaves the brainstem at a higher position than Cranial nerve XII, whose origin is located more caudally (lower) than the other cranial nerves.

# Name Nuclei Function
0 Cranial nerve zero (CN0 is not traditionally recognized.)[1] olfactory trigone, medial olfactory gyrus, and lamina terminalis

Still controversial

New research indicates CN0 may play a role in the detection of pheromones [2][3]

I Olfactory nerve Anterior olfactory nucleus Transmits the sense of smell; Located in olfactory foramina of ethmoid
II Optic nerve Lateral geniculate nucleus Transmits visual information to the brain; Located in optic canal
III Oculomotor nerve Oculomotor nucleus, Edinger-Westphal nucleus Innervates levator palpebrae superioris, superior rectus, medial rectus, inferior rectus, and inferior oblique, which collectively perform most eye movements; Located in superior orbital fissure
IV Trochlear nerve Trochlear nucleus Innervates the superior oblique muscle, which depresses, pulls laterally, and intorts the eyeball; Located in superior orbital fissure
V Trigeminal nerve 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 superior orbital fissure (ophthalmic branch), foramen rotundum (maxillary branch), and foramen ovale (mandibular branch)
VI Abducens nerve Abducens nucleus Innervates the lateral rectus, which abducts the eye; Located in superior orbital fissure
VII Facial nerve Facial nucleus, Solitary nucleus, Superior salivary nucleus Provides motor innervation to the muscles of facial expression and stapedius, 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 and runs through internal acoustic canal to facial canal and exits at stylomastoid foramen
VIII Vestibulocochlear nerve (or auditory-vestibular nerve or statoacustic nerve) Vestibular nuclei, Cochlear nuclei Senses sound, rotation and gravity (essential for balance & movement; Located in internal acoustic canal
IX Glossopharyngeal nerve 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 (essential for tactile, pain, and thermal sensation). Sensation is relayed to opposite thalamus and some hypothalamic nuclei. Located in jugular foramen
X Vagus nerve Nucleus ambiguus, Dorsal motor vagal nucleus, Solitary nucleus Supplies branchiomotor innervation to most laryngeal and pharyngeal muscles; provides parasympathetic fibers to nearly all thoracic and abdominal viscera down to the splenic flexure; and receives the special sense of taste from the epiglottis. A major function: controls muscles for voice and resonance. Symptoms of damage: dysphagia (swallowing problems). Located in jugular foramen
XI Accessory nerve (or cranial accessory nerve or spinal accessory nerve) Nucleus ambiguus, Spinal accessory nucleus Controls muscles of the neck and overlaps with functions of the vagus. Examples of symptoms of damage: inability to shrug, weak head movement, velopharyngeal insufficiency; Located in jugular foramen
XII Hypoglossal nerve Hypoglossal nucleus Provides motor innervation to the muscles of the tongue and other glossal muscles. Important for swallowing (bolus formation) and speech articulation. Located in hypoglossal canal

Nerves and nuclei

As well as the visible nerves outside of the brain, most of the cranial nerves have associated nuclei within the brainstem. These nuclei are areas of grey matter, and damage to them can have a similar affect to the severing of an actual nerve. Axons to (and from) cranial nerves synapse first at the nuclei.

Arrangement of the nuclei

Just as grey matter in the ventral (closer to front of a human) spinal cord tends to be efferent (motor) fibers, and the dorsal horn tends to contain sensory neurons, nuclei in the brainstem are arranged in an analogous way.

  • Close to the midline are the somatic efferent nuclei, such as the oculomotor nucleus, which control skeletal muscle. Just lateral to this are the autonomic (or visceral) efferent nuclei (for instance, the Edinger-Westphal nucleus, which controls tears).
  • There is a separation, called the sulcus limitans, and lateral to this are the sensory nuclei. Near the sulcus limitans are the visceral afferent nuclei, namely the solitary tract nucleus.
  • More lateral, but also less posterior, are the general somatic afferent nuclei. This is the trigeminal nucleus. Back at the dorsal surface of the brainstem, and more lateral are the special somatic afferents, this handles sensation such as balance.
  • Another area, not on the dorsum of the brainstem, is where the branchial efferent nuclei reside. These formed from the branchial arches, in the embryo. This area is a bit below the autonomic motor nuclei, and includes the nucleus ambiguus, facial nerve nucleus, as well as the motor part of the trigeminal nerve nucleus.


Cranial nerves in non-human vertebrates

Human cranial nerves are evolutionarily homologous to those found in many other vertebrates. Cranial nerves XI and XII evolved in the common ancestor to amniotes (non-amphibian tetrapods) thus totalling twelve pairs. These characters are synapomorphies for their respective clades. In some primitive cartilagenous fishes, such as the dogfish (Squalos acanthos), there is a terminal nerve numbered zero (as it exits the brain before the first cranial nerve).

Mnemonic devices

As the list is important to keep in mind during the examination of the nervous system, 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. The best known example is, "On Old Olympus' Towering Tops A Finn And German Viewed Some Hops,"[4] where And represents auditory vestibular and Some represents spinal accessory. There are numerous mnemonics one example: "Ohh, Ohh, Oh, To Touch And Feel Virgin Girls' Vaginas And Hymens"

Another to help remember the types of information these nerves carry (sensory, motor, or both) is thus:

  • Some Say Money Matters, But My Brother Says Big Boobs Matter More.

For additional memonics, see b:Transwiki:List of mnemonics for the cranial nerves


Thirteen cranial nerves?

Although twelve nerves are classically described in humans, there is a theory that finds favour with some authors, that humans really have thirteen cranial nerves (Andy Lelli , 1999). If the C1 spinal nerve were considered the thirteenth cranial nerve, C2 through C8 would be renamed as the first through seventh cervical nerves (though anatomists might change the term 'cervical' to 'nuchal' or some other term to avoid confusion between the two nomenclatures). This would make the numbering system consistent all the way through the spinal column - every nerve would exit below its corresponding vertebra, and the number of vertebrae would equal the number of spinal nerves.

Alternatively, C1 could be considered the spinal root of the hypoglossal nerve (CN XII). This would, again, make the numbering system consistent.

See also

External links

References

  1. Fuller GN, Burger PC. "Nervus terminalis (cranial nerve zero) in the adult human." Clin Neuropathol 9, no. 6 (Nov-Dec 1990): 279-283.
  2. Merideth, Michael. "Human Vomeronasal Organ Function." Oxford Journals: Chemical Senses, 2001.
  3. Fields, R. Douglas. "Sex and the Secret Nerve." Scientific American Mind, February 2007.
  4. Herlevich NE (1990). Reflecting on old Olympus' towering tops. Journal of ophthalmic nursing & technology 9 (6): 245–6.
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This page uses Creative Commons Licensed content from Wikipedia (view authors).

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