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In neuroanatomy, the optic chiasm, or optic chiasma (/ ɒ p t ɪ k k aɪ æ z əm /; from Greek χίασμα 'crossing', from Ancient Greek χιάζω 'to mark with an X'), is the part of the brain where the optic nerves cross. It is located at the bottom of the brain immediately inferior to the hypothalamus. [1]
The fibers 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. A fundus photograph showing the back of the retina. The white circle is the beginning of the optic nerve. The optic nerve is composed of retinal ganglion cell axons and glia.
The oculomotor nerve originates from the third nerve nucleus at the level of the superior colliculus (in non-mammalian vertebrates this is the optic tectum) in the midbrain. The rostral part of the nerve crosses the midline to merge with the part of the contralateral nerve that does not cross. Since the midline crossing occurs inside the brain ...
It is a small, ovoid, ventral projection of the thalamus where the thalamus connects with the optic nerve. There are two LGNs, one on the left and another on the right side of the thalamus. In humans, both LGNs have six layers of neurons (grey matter) alternating with optic fibers (white matter).
In neuroanatomy, the optic tract (from Latin tractus opticus) is a part of the visual system in the brain.It 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.
Schematic diagram of the human eye, with the optic disc, or blind spot, at the lower left. Shown is a horizontal cross section of the right eye, viewed from above. A normal optic disc is orange to pink in colour and may vary based on ethnicity. [3] A pale disc is an optic disc which varies in colour from a pale pink or orange colour to white. A ...
Retina→Optic nerve→Optic chiasma (here the nasal visual field of both eyes cross over to the opposite side)→Optic tract→Lateral geniculate body→Optic radiation→Primary visual cortex. The type of field defect can help localize where the lesion is located (see picture given in infobox).
Fibers from the optic nerves cross over in the optic chiasm with some fibers passing to the contralateral optic nerve tract. This is the basis of the " swinging-flashlight test ". Loss of accommodation and continued pupillary dilation can indicate the presence of a lesion on the oculomotor nerve.