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The optic chiasm is found in all vertebrates, although in cyclostomes (lampreys and hagfishes), it is located within the brain. [2] [3] This article is about the optic chiasm of vertebrates, which is the best known nerve chiasm, but not every chiasm denotes a crossing of the body midline (e.g., in some invertebrates, see Chiasm (anatomy)).
Gliomas of the optic chiasm are usually derived from astrocytes. These tumors are slow growing and more often found children. [2] However, they have a worse prognosis, especially if they have extended into the hypothalamus. They are frequently associated with neurofibromatosis type 1 (NF-1). Their treatment involves the resection of the optic ...
The optic tract is a continuation of the optic nerve that relays information from the optic chiasm to the ipsilateral lateral geniculate nucleus (LGN), pretectal nuclei, and superior colliculus. [14] The optic tract represents the first stage in the visual pathway in which visual information is transferred in a homonymous nature. [15]
Chiasms are found in vertebrates but also in invertebrates. The optic chiasm in vertebrates can be of type I or II. [1] [4] However, an optic chiasm of type III is found in many insects [2] and in cephalopods. [3] In vertebrates, three of the cranial nerves show a chiasm. The optic chiasm of the optic tract (type I or II)
The opening of each optic canal is placed at either lateral end of the chiasmatic sulcus. The optic chiasm is situated superior and quite posterior to the chiasmatic groove (and not against the groove as the name suggests).
Optic gliomas are usually pilocytic tumors, and can involve the optic nerve or optic chiasm. [3] Optic gliomas are usually associated with neurofibromatosis type 1 in 30% of people with the condition. [3] Optic nerve gliomas have low mortality but extremely high prevalence of vision loss and eye-bulging exophthalmos) in children. [4]
Chiasm (anatomy), an X-shaped structure produced by the crossing over of the fibers, with the prefix chiasm- means cross examples include: A nerval chiasm, where either two nerves cross in the body midline (e.g. Optic chiasma) A crossing of fibres inside a nerve reversing their mapping; A tendinous chiasm, the spot where two tendons cross.
The optic tract grows from the retina to the optic tectum. Because dorsal and ventral are inverted in the anterior head region, the tracts grow at first toward the ventral side, to meet in the midline to form a chiasma. Since the optic tectum lies on the dorsal midbrain, each tract then continues dorsally to the contralateral optic tectum. [10]