Cranial nerves
| Nerve: Cranial nerves | |
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| Inferior view of the brain and brain stem showing cranial nerves. An unlabelled version is here | |
| Latin | nervus cranialis (plural: nervi craniales) |
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 12 pairs of cranial nerves. Only the first and the second pair emerge from the cerebrum, the remaining 10 pairs emerge from the brainstem.
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Origin and function
The trochlear nucleus is unique in that its axons run dorsally and cross the midline before emerging from the brainstem. Thus a lesion of the trochlear nucleus affects the contralateral eye. Lesions of all other cranial nuclei affect the ipsilateral side (except of course the optic nerves - cranial nerves II - which innervate both eyes).
Cranial nerves in non-human vertebrates
Human cranial nerves are nerves 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 totaling twelve pairs. These characters are synapomorphies for their respective clades. In some primitive cartilaginous fishes, such as the spiny dogfish or mud shark (Squalus acanthias), there is a terminal nerve numbered zero (as it exits the brain before the traditionally designated first cranial nerve).
List of cranial nerves
| # | Name | Sensory, Motor or Both |
Origin | Nuclei | Function |
| 0 | Cranial nerve zero (CN0 is not traditionally recognized.)[1] | Sensory | olfactory trigone, medial olfactory gyrus, and lamina terminalis |
New research indicates CN0 may play a role in the detection of pheromones [2][3] Linked to olfactory system in human embryos[4] |
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| I | Olfactory nerve | Purely Sensory | Anterior olfactory nucleus | Transmits the sense of smell; Located in olfactory foramina in the Cribiform plate of ethmoid | |
| II | Optic nerve | Purely Sensory | Ganglion cells of retina[5] | Transmits visual information to the brain; Located in optic canal | |
| III | Oculomotor nerve | Mainly Motor | Midbrain | Oculomotor nucleus, Edinger-Westphal nucleus | Innervates levator palpebrae superioris, superior rectus, medial rectus, inferior rectus, and inferior oblique, which collectively perform most eye movements; Also innervates m. sphincter pupillae. Located in superior orbital fissure |
| IV | Trochlear nerve | Mainly Motor | Midbrain | Trochlear nucleus | Innervates the superior oblique muscle, which depresses, rotates laterally (around the optic axis), and intorts the eyeball; Located in superior orbital fissure |
| V | Trigeminal nerve | 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 superior orbital fissure (ophthalmic nerve - V1), foramen rotundum (maxillary nerve - V2), and foramen ovale (mandibular nerve - V3) |
| VI | Abducens nerve | Mainly Motor | Posterior margin of Pons | Abducens nucleus | Innervates the lateral rectus, which abducts the eye; Located in superior orbital fissure |
| VII | Facial nerve | 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, and stapedius muscle, 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 statoacoustic nerve) | Mostly sensory | Lateral to CN VII (cerebellopontine angle) | Vestibular nuclei, Cochlear nuclei | Senses sound, rotation and gravity (essential for balance & movement). More specifically. the vestibular branch carries impulses for equilibrium and the cochlear branch carries impulses for hearing.; Located in internal acoustic canal |
| IX | Glossopharyngeal nerve | 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 (essential for tactile, pain, and thermal sensation). Some sensation is also relayed to the brain from the palatine tonsils. Sensation is relayed to opposite thalamus and some hypothalamic nuclei. Located in jugular foramen |
| X | Vagus nerve | Both Sensory and Motor | Posterolateral sulcus of Medulla | Nucleus ambiguus, Dorsal motor vagal nucleus, Solitary nucleus | Supplies branchiomotor innervation to most laryngeal and all pharyngeal muscles (except the stylopharyngeus, which is innervated by the glossopharyngeal); 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 and the soft palate. Symptoms of damage: dysphagia (swallowing problems), velopharyngeal insufficiency. Located in jugular foramen |
| XI | Accessory nerve (or cranial accessory nerve or spinal accessory nerve) | Mainly Motor | Cranial and Spinal Roots | Nucleus ambiguus, Spinal accessory nucleus | Controls sternocleidomastoid and trapezius muscles, overlaps with functions of the vagus. Examples of symptoms of damage: inability to shrug, weak head movement; Located in jugular foramen |
| XII | Hypoglossal nerve | Mainly Motor | Medulla | Hypoglossal nucleus | Provides motor innervation to the muscles of the tongue (except for the palatoglossus, which is innervated by the vagus) and other glossal muscles. Important for swallowing (bolus formation) and speech articulation. Located in hypoglossal canal |
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. Two of the best known examples are, "Oh, Oh, Oh To Take A Family Vacation! Go Vegas After Hours!", or "On Old Olympus' Towering Top, A Finn And German Viewed A Hop". Others are more explicit, for example: "On the Occasion Of Party The Attractive Faces Are Girl Visitors, Say Hello".Its also "OOOPTAFAGV SH"
A very useful way of remembering which nerve is motor and which is sensory use, "Some Say Marry Money But My Brother Says Big Boobs Matter More". Although many exist from many sources, for example OLd OPie OCcasionally TRies TRIGonometry And Feels VEry GLOomy, VAGUe, And HYPOactive.[6]
Cribiform plate (Olfactory), Optic canal (Optic), Superior Orbital Fissure (Oculomotor), Superior Orbital Fissure (Pathetic/Trochlear), Superior Orbital Fissure (Trigeminal - Ophthalmic), Foramen Rotundum (Trigeminal - Maxillary), Foramen Ovale (Trigeminal - Mandibular), Superior Orbital Fissure (Abducens), Internal Acoustic Meatus (Facial), Internal Acoustic Meatus (Auditory/Vestibulocochlear), Jugular Foramen (Glossopharyngeal), Jugular Foramen (Vagus), Jugular Foramen ( Spinal Accessory), Hypoglossal Canal (Hypoglossal Nerve)
See also
- Cranial nerve nucleus
- List of mnemonics for the cranial nerves
- Cranial nerve examination
References
- ↑ Fuller GN, Burger PC. "Nervus terminalis (cranial nerve zero) in the adult human." Clin Neuropathol 9, no. 6 (Nov-Dec 1990): 279-283.
- ↑ Merideth, Michael. "Human Vomeronasal Organ Function." Oxford Journals: Chemical Senses, 2001.
- ↑ Fields, R. Douglas. "Sex and the Secret Nerve." Scientific American Mind, February 2007.
- ↑ Müller F, O'Rahilly R (2004). "Olfactory structures in staged human embryos". Cells Tissues Organs (Print) 178 (2): 93–116. doi:10.1159/000081720. PMID 15604533.
- ↑ Henry Gray (1821–1865). Anatomy of the Human Body. 1918.
- ↑ Saladin, Kenneth S. (2008). Human anatomy (Second Edition). McGraw-Hill Higher Education. ISBN 0071102094, 9780071102094.
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