The Cranial Nerves

Information about The Cranial Nerves

Cranial nerves

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
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
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
XII	Hypoglossal nerve	Hypoglossal nucleus	Provides motor innervation to the intrinsic muscles of the tongue and other glossal muscles

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

Main article: List of mnemonics for the cranial nerves

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. Examples are:

On Old Olympus Towering Tops, A Finn And German Viewed Some Hops.
OLd OPie OCcasionally TRies TRIGonometry And Feels VEry GLOomy, VAGUe, And HYPOactive
On Occasion Our Trusty Truck Acts Funny. Very Good Vehicle Any How.

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.

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.

• • [ e] Nerves of head and neck: the cranial nerves
I-IV	olfactory • optic • oculomotor (superior branch, inferior branch) • trochlear
V: trigeminal	trigeminal ganglion • ophthalmic • maxillary • mandibular
VI: abducens	no significant branches
VII: facial	nervus intermedius • geniculate • inside facial canal (greater petrosal, nerve to the stapedius, chorda tympani) • at exit from stylomastoid foramen (posterior auricular, digastric • stylohyoid) • on face (temporal, zygomatic, buccal, mandibular, cervical)
VIII: vestibulocochlear	cochlear (striae medullares, lateral lemniscus) • vestibular (Scarpa's ganglion)
IX: glossopharyngeal	nucleus ambiguus • ganglia (superior, petrous) • tympanic (tympanic plexus, lesser petrosal) • carotid sinus • pharyngeal branches • pharyngeal plexus
X: vagus	ganglia (jugular, nodose) • Alderman's nerve • in the neck (pharyngeal branch, superior laryngeal ext and int, recurrent laryngeal) • in the thorax (pulmonary branches, esophageal plexus) • in the abdomen (gastric plexuses, celiac plexus, gastric plexus)
XI-XII	accessory • hypoglossal

A nerve is an enclosed, cable-like bundle of axons (the long, slender projection of a neuron). Neurons are sometimes called nerve cells, though this term is technically imprecise since many neurons do not form nerves, and nerves also include the glial cells that
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In animals, the brain or encephalon (Greek for "in the skull"), is the control center of the central nervous system, responsible for behavior. The brain is located in the head, protected by the skull and close to the primary sensory apparatus of vision, hearing,
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The term spinal nerve generally refers to the mixed spinal nerve, which is formed from the dorsal and ventral roots that come out of the spinal cord. The spinal nerve is the bit that passes out of the vertebrae through the intervertebral foramen.
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spinal chord is a thin, tubular bundle of nerves that is an extension of the central nervous system from the brain and is enclosed in and protected by the bony vertebral column.
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Human anatomy is primarily the scientific study of the morphology of the adult human body.^[1] It is subdivided into gross anatomy and microscopic anatomy.^[1]
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The brain stem is the lower part of the brain, adjoining and structurally continuous with the spinal cord. Most sources consider the pons, medulla oblongata, and midbrain all to be part of the brainstem.
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MUSCLE (multiple sequence comparison by log-expectation) is public domain, multiple sequence alignment software for protein and nucleotide sequences.
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sensory system: in this case, vision, for the visual system. ]]

A sensory system is a part of the nervous system responsible for processing sensory information.
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Head and neck anatomy focuses on the structures of the head and neck of the human body, including the brain, bones, muscles, blood vessels, nerves, glands, nose, mouth, teeth, tongue, and throat.
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The Peripheral nervous system resides or extends outside the "CNS" central nervous system (the brain and spinal cord) to serve the limbs and organs. Unlike the central nervous system, however, the PNS is not protected by bone, leaving it exposed to toxins and mechanical injuries.
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Segmental innervation refers to the distribution (innervation) of nerves within an organ or muscle. These nerves are attached to a segment of the spine. ^[1]

Segmental innervation can be mapped through stimulation of the nerve at the spinal segment.
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Roman numerals is a numeral system originating in ancient Rome, adapted from Etruscan numerals. The system used in classical antiquity was slightly modified in the Middle Ages to produce the system we use today. It is based on certain letters which are given values as numerals.
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In neuroanatomy, a nucleus is a central nervous system structure that is composed mainly of gray matter, and that acts as a hub or transit point for electrical signals in a single neural subsystem.
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The terminal nerve, or cranial nerve zero, was discovered by German scientist Gustav Fritsch in 1878 in the brains of sharks. It was first found in humans in 1913,^[1] although its presence in humans remains controversial.
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The olfactory trigone is a small triangular area in front of the anterior perforated substance.

Its apex, directed forward, occupies the posterior part of the olfactory sulcus, and is brought into view by throwing back the olfactory tract.
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The median portion of the wall of the fore-brain vesicle consists of a thin lamina, the lamina terminalis, which stretches from the interventricular foramen to the recess at the base of the optic stalk.
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The olfactory nerve, or cranial nerve I, is the first of twelve cranial nerves. The specialized olfactory receptor neurons of the olfactory nerve are located in the olfactory mucosa of the upper parts of the nasal cavity.
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The anterior olfactory nucleus (AON; also called the anterior olfactory cortex) is a portion of the forebrain of vertebrates. It is found behind the olfactory bulb and in front of the piriform cortex (laterally) and olfactory tubercle (medially) in a region often referred to as
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Optic Nerve may be a reference to:

Optic nerve, the anatomical structure;
Optic Nerve (comic), the comic book series;
Optic Nerve (1998), the seminal release from the Irish hip hop act known as Exile Eye; or

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The lateral geniculate nucleus (LGN) of the thalamus is a part of the brain, which is the primary processor of visual information, received from the retina, in the central nervous system.
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The oculomotor nerve is the third of twelve paired cranial nerves. It controls most of the eye movements (cranial nerves IV and VI also do some), constriction of the pupil, and holding the eyelid open.
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The fibers of the oculomotor nerve arise from a nucleus in the midbrain, which lies in the gray substance of the floor of the cerebral aqueduct and extends in front of the aqueduct for a short distance into the floor of the third ventricle.
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The Edinger-Westphal nucleus (also known as the accessory oculomotor nucleus ) is the accessory parasympathetic cranial nerve nucleus of the oculomotor nerve (cranial nerve III), supplying the constricting muscles of the iris.
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The trochlear nerve (the fourth cranial nerve, also called the fourth nerve or simply IV) is a motor nerve (a “somatic efferent” nerve) that innervates a single muscle: the superior oblique muscle of the eye.
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The nucleus of the trochlear nerve is located in the midbrain, at the level of the inferior colliculus. It is a motor nucleus, so located near the midline.

Oddly, fibers from the trochlear nucleus cross over in the midbrain at the superior medullary velum and exit
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The trigeminal nerve (the fifth cranial nerve, also called the fifth nerve or simply V) is responsible for sensation in the face. It is similar to the spinal nerves C2–S5, which are responsible for sensation in the rest of the body.
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The principal sensory nucleus (or chief sensory nucleus) receives information about discriminative sensation and light touch as well as conscious proprioception of the jaw.
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The spinal trigeminal nucleus receives information about light touch, pain, and temperature from the ipsilateral face. The facial, glossopharyngeal, and vagus nerves also convey pain information from their areas to the spinal trigeminal nucleus.
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The mesencephalic nucleus is involved with proprioception, that is, the feeling of position of the muscles. Unlike many nuclei within the CNS, the mesencephalic nucleus contains no synapses.
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The trigeminal motor nucleus contains motor neurons that innervate muscles of the first branchial arch, namely the muscles of mastication, the tensor tympani, tensor veli palatini, mylohyoid, and anterior belly of the digastric.
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