Definition, Betydelse & Anagram | Engelska ordet CHIASMA

Definition av CHIASMA

1. (anatomi, genetik) chiasma

Exempel på hur man kan använda CHIASMA i en mening

• In humans, the optic nerve is derived from optic stalks during the seventh week of development and is composed of retinal ganglion cell axons and glial cells; it extends from the optic disc to the optic chiasma and continues as the optic tract to the lateral geniculate nucleus, pretectal nuclei, and superior colliculus.
• At least one chiasma per chromosome often appears to be necessary to stabilise bivalents along the metaphase plate during separation.
• Superior hemianopsia – the upper half of the field of vision is affected, possibly because of a tumor beginning to compress the lower part of the chiasma, typically one from the hypophysis.
• The superior surface of the sphenoid bone is bounded behind by a ridge, which forms the anterior border of a narrow, transverse groove, the chiasmatic groove (optic groove), above and behind which lies the optic chiasma; the groove ends on either side in the optic foramen, which transmits the optic nerve and ophthalmic artery (with accompanying sympathetic nerve fibres) into the orbital cavity.
• Occupying the posterior part of the commissure of the optic chiasma is a strand of fibers, the Ventral supraoptic decussation (commissure of Gudden, Gudden's inferior commissure), which is not derived from the optic nerves; it forms a connecting link between the medial geniculate bodies.
• At the junction of the floor and anterior wall of the third ventricle, immediately above the optic chiasma, the ventricle presents a small angular recess or diverticulum, the optic recess (or supraoptic recess).
• The interpeduncular fossa is in front by the optic chiasma, behind by the antero-superior surface of the pons, antero-laterally by the converging optic tracts, and postero-laterally by the diverging cerebral peduncles.
• In neuroanatomy, the term chiasma is reserved for crossing of- or within nerves such as in the optic chiasm.
• brunneus was exposed to X-irradiation during the zygotene-early pachytene stages of meiosis, this treatment caused a significant increase in meiotic cell chiasma frequency.
• In the holocephalan species Chimaera monstrosa (ratfish), he described, in the basal midline of the diencephalon, a previously unknown ependymall structure adjacent to the rostral part of the optic chiasma referred to as the ‘organon vasculare praeopticum’.
• Points of crossing over become visible as chiasma after the synaptonemal complex dissembles and the homologous chromosomes slightly apart from each other.
• Combined cytological and autoradiographic analyses of meiosis showed that crossing over is achieved by breakage and exchange of segments of nonsister, homologous chromatids, and each such exchange event results in the formation of a cytologically visible chiasma.
• However, holocentric chromosomes may also present limitations to crossing over, causing a restriction of the number of chiasma in bivalents, and may cause a restructuring of meiotic divisions resulting in an "inverted" meiosis.
• Middle chiasmal syndrome, the lesions involving the decussating fibres in the body of chiasma produce bitemporal hemianopia.

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