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 (kī-ăz′mə) also chi·asm (kī′ăz′əm)
n. pl. chi·as·ma·ta (-mə-tə) or chi·as·mas also chi·asms
1. Anatomy A crossing or intersection of two tracts, as of nerves or ligaments.
2. Genetics The point of contact between paired chromatids during meiosis, resulting in a cross-shaped configuration and representing the cytological manifestation of crossing over.

[Greek khīasma, cross-piece, from khīazein, to mark with an X, from khei, khī, chi (from the letter's shape).]

chi·as′mal, chi·as′mic, chi′as·mat′ic (-măt′ĭk) adj.
ThesaurusAntonymsRelated WordsSynonymsLegend:
Noun1.chiasm - an intersection or crossing of two tracts in the form of the letter X
anatomical structure, bodily structure, body structure, complex body part, structure - a particular complex anatomical part of a living thing; "he has good bone structure"
chiasma opticum, optic chiasm, optic chiasma - the crossing of the optic nerves from the two eyes at the base of the brain


, chiasma
n. quiasma.
1. cruzamiento de dos vías o conductos;
2. punto de cruzamiento de las fibras de los nervios ópticos.
References in periodicals archive ?
At necropsy, a conical, solid tan mass with 10 cm-length was observed involving the optic nerve from the posterior aspect of the right globe to the optic chiasm. Its thickness varied from 0.5 cm (in the optic chiasm region) to 3 cm (in the remaining areas of the tumor) (Figure 1A, B, C).
For example, unilateral damage to VI, the optic tract (the section of the pathway that relays information from the optic chiasm to the LGN), or the LGN itself can lead to contralateral homonymous hemianopia (see Figure 2b), (9) while unilateral damage to Meyer's loop of the optic radiations often results in homonymous quadrantanopia (see Figure 2c).
But sometimes lists of producers, DJs electronic acts seem so alien to us* they shift around before the eye can fully hone in, before the information can pass from retina to optic nerve, through optic chiasm, photoreceptor and synapses It's like that creepy hypnotism scene in Stir Of Echoes when Kevin Bacon is staring at the movie screen, straining to bring the blurry words into focus.
Its use is recommended for large adenomas (>3cm) and for tumours located at the distance of 3-5mm from optic chiasm.
Chordoid glioma of the third ventricle attached to the optic chiasm. Successful removal through a trans-lamina terminalis approach.
There is often obliteration of the prepontine and perichiasmatic cisterns, with flattening of the pons and draping of the optic chiasm over the dorsum sella.
Diffusion magnetic resonance imaging (MRI) revealed extending nodular enhancements within and adjacent to the optic chiasm, at the basal cisternal level, and in the leptomeningeal layers in the posterior fossa.
Diffuse malignant lymphoma type B with optic chiasm infiltration, visual disturbances, hypopituitarism, hyperprolactinaemia and diabetes insipidus.
In fact, GH and GH mRNA proteins have also been identified in retinal ganglion cells and can be traced within their axons in the retina within the optic fibre layer and outside the retina within the optic nerve, optic chiasm and optic tract (10,15,16).
The optic nerve passing optic canal ran from the eyeball to the optic chiasm; the optic tract ran from the optic chiasm to the lateral geniculate nucleus; the optic radiation ran from the lateral geniculate nucleus to the calcarine sulcus (Fig.
Specialists in ophthalmology and radiology cover examination of the afferent visual system, visual fields, magnetic resonance imaging for the ophthalmologist, transient visual loss/retinal artery occlusion, optic nerve disorders, optic chiasm, retrochiasmal disorders, non-physiologic visual loss, neuro-ophthalmologic examinations--efferent systems, ocular misalignment and other ocular motor disorders, nystagmus, pupil, and orbital disease of neuro-ophthalmic significance.
Joudah exploits the fuzziness of language from the outset, toying with false chiasms and faux epigrams like "the falafel of truth / and the truth of falafel." Bathetic, ironic, and obscure by turns, the books first section complicates the "common" with roundabout epithets like "the grackle, common, / indigo, icteric-eyed New World // passerine." Associations that hinge on sonic rather than semiotic connections ("not chasm but chiasm") and moments of ambiguous syntax foreground words as words, functioning originally in their "status as feeling." The question of origins, too, recurs throughout Footnotes.