Cranial nerves

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Cranial nerves

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]


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
II Optic nerve Lateral geniculate nucleus Transmits visual information to the brain
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
IV Trochlear nerve Trochlear nucleus Innervates the superior oblique muscle, which depresses, pulls laterally, and intorts the eyeball
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
VI Abducens nerve Abducens nucleus Innervates the lateral rectus, which abducts the eye
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
VIII Vestibulocochlear nerve (or auditory-vestibular nerve or statoacustic nerve) Vestibular nuclei, Cochlear nuclei Senses sound, rotation and gravity (essential for balance & movement)
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.
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).
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)
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.

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 Top A Finn And German Viewed Some Hops,"[4] where And represents auditory vestibular and Some represents spinal accessory.

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 Brains Matter More.

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. PMID 2254946. 



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