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Cranial nerve From Wikipedia, the free encyclopedia Jump to: navigation, search Nerve: Cranial nerves Inferior view of the brain and brain stem showing cranial nerves. An unlabelled version is here Latin nervus cranialis (plural: nervi craniales) Code TA A14.2.00.038 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[edit source | editbeta] 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. Cranial nerve zero The terminal nerve appears just ahead of the other cranial nerves bilaterally as a microscopic plexus of unmyelinated peripheral nerve fascicles in the subarachnoid space that covers gyrus rectus. This plexus appears near the cribriform plate and travels posteriorly toward the olfactory trigone, medial olfactory gyrus, and lamina terminalis.[2] The nerve is often overlooked in autopsies because it is unusually thin for a cranial nerve, and is often torn out upon exposing the brain.[3] Careful dissection is necessary to visualize the nerve. Its purpose and mechanism of function is still open to debate; consequently, nerve zero is often not mentioned in anatomy textbooks.[1] Function[edit source | editbeta] Although very close to[4] (and often confused for a branch of) the olfactory nerve, nerve zero is not connected to the olfactory bulb, where smells are analyzed. This fact suggests that the nerve is either vestigial or may be related to the sensing of pheromones. This hypothesis is further supported by the fact that nerve zero projects to the medial and lateral septal nuclei, and the preoptic areas, all of which are involved in regulating sexual behavior in mammals.[1] Development[edit source | editbeta] The zebrafish has been used as a developmental model in recent research.[5] The connections between cranial nerve zero and the olfactory system has been extensively studied in human embryos. It was found to enter the brain at stages 17 and 18 from olfactory origins. Olfactory nerve From Wikipedia, the free encyclopedia Jump to: navigation, search Nerve: Olfactory nerve The Olfactory Nerve Inferior view of the human brain, with the cranial nerves labelled. Latin nervus olfactorius MeSH Olfactory+Nerve Cranial nerves 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 This box: view · talk · edit Optic nerve The olfactory nerve, or cranial nerve I, is the first of twelve pairs of cranial nerves. It is instrumental in the sense of smell. Derived from the embryonic nasal placode, the olfactory nerve is capable of regeneration. The olfactory nerve is sensory in nature and originates on the olfactory mucosa in the anterosuperior nasal cavity.[1] From the olfactory mucosa, the nerve travels down the olfactory tract until it reaches the olfactory bulb, where the fascicles of the olfactory nerve pass through foramina on the cribriform plate, which resides on the roof of the nasal cavity. These fascicles are not visible on a cadaver brain because they are severed upon removal The optic nerve is the second of twelve paired cranial nerves but is considered to be part of the central nervous system, as it is derived from an outpouching of the diencephalon during embryonic development. As a consequence, the fibers are covered with myelin produced by oligodendrocytes, rather than Schwann cells, which are found in the peripheral nervous system, and are encased within the meninges. Peripheral neuropathies like Guillain-Barré syndrome do not affect the optic nerve. The optic nerve is ensheathed in all three meningeal layers (dura, arachnoid, and pia mater) rather than the epineurium, perineurium, and endoneurium found in peripheral nerves. Fiber tracks of the mammalian central nervous system (as opposed to the peripheral nervous system) are incapable of regeneration, and, hence, optic nerve damage produces irreversible blindness. The fibres from the retina run along the optic nerve to nine primary visual nuclei in the brain, from which a major relay inputs into the primary visual cortex. Oculomotor nerve From Wikipedia, the free encyclopedia Jump to: navigation, search Nerve: Oculomotor nerve Nerves of the orbit. Seen from above. Inferior view of the human brain, with the cranial nerves labelled. Latin nervus oculomotorius Gray's subject #198 884 Innervates Superior rectus, Inferior rectus, Medial rectus, Inferior oblique, Levator palpebrae, sphincter pupillae (parasympathetics), ciliaris muscle (parasympathetics) From oculomotor nucleus, Edinger-Westphal nucleus To superior branch, inferior branch MeSH Oculomotor+Nerve Cranial nerves 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 The oculomotor nerve is the 3rd of 12 paired cranial nerves. It enters the orbit via the superior orbital fissure and controls most of the eye's movements, including constriction of the pupil and maintaining an open eyelid by innervating the levator palpebrae superioris muscle. The oculomotor nerve is derived from the basal plate of the embryonic midbrain. Cranial nerves IV and VI also participate in control of eye movement.