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Cranial Nerve

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Cranial Nerve

Nerve: Cranial nerves
Inferior view of the here
Latin nervus cranialis (plural: nervi craniales)
Code

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. Only the first and the second pair 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 or 'optic nerve', along with the retina, which is not a true peripheral nerve but a tract of the diencephalon.[1] Cranial nerve ganglia originate in the central nervous system (CNS). The remaining eleven axons extend beyond the brain and are therefore considered part of the PNS.[2]

Cranial nerves in non-human vertebrates

Human cranial nerves are nerves similar to those found in many other vertebrates. Cranial nerves XI and XII evolved in other species to amniotes (non-amphibian tetrapods), thus totaling twelve pairs. In some primitive cartilaginous fishes, such as the spiny dogfish or mud shark (Squalus acanthias), there is a terminal nerve numbered zero, since it exits the brain before the traditionally designated first cranial nerve.


List of cranial nerves

Number Name Sensory,
motor,
or both
Origin/Target Nuclei Function
I Olfactory Purely sensory Telencephalon Anterior olfactory nucleus Transmits the sense of smell from the nasal cavity.[3] Located in olfactory foramina in the cribriform plate of ethmoid.
II Optic Purely sensory Retinal ganglion cells Lateral geniculate nucleus[4] Transmits visual signals from the retina of the eye to the brain.[5] 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 Acoustic or Vestibulocochlear (or auditory-vestibular nerve 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 or spinal-accessory (or cranial accessory nerve or spinal accessory nerve) 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,"[6] and for the initial letters "OOOTTAFVGVAH" is "Oh, oh, oh, to touch and feel very good velvet...ah, heaven."[7] The differences between these depend on "acoustic" versus "vestibulocochlea" 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 Boobs Matter More". There are many more mnemonics from many sources, for example OLd OPie OCcasionally TRies TRIGonometry And Feels VEry GLOomy, VAGUe, And HYPOactive.[8]

See also

References

Additional images

External links

Animations of cranial nerve input to here (University of Liverpool Veterinary School).

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