Optic chiasm

Optic chiasm
Brain: Optic chiasm
Visual pathway with optic chiasm (X shape outlined, red) (1543 image from Andreas Vesalius' Fabrica)
Latin chiasma opticum
Gray's subject #197 883
MeSH Optic+chiasm
NeuroLex ID birnlex_1416

The optic chiasm or optic chiasma (Greek χίασμα, "crossing", from the Greek χιαζω 'to mark with an X', after the Greek letter 'Χ', chi) is the part of the brain where the optic nerves (CN II) partially cross. The optic chiasm is located at the bottom of the brain immediately below the hypothalamus.[1]



The images on the nasal sides of each retina cross over to the opposite side of the brain via the optic nerve at the optic chiasm. The temporal images, on the other hand, stay on the same side. This allows the images from either side of the field from both eyes to be transmitted to the appropriate side of the brain, combining the sides together. Beyond the optic chiasm, with crossed and uncrossed fibers, optic nerves become optic tracts. This allows for parts of both eyes that attend to the right visual field to be processed in the left visual system in the brain, and vice versa. This is linked to skin sensation which reaches the opposite side of the body, after reaching the diencephalon (rear forebrain). Decussation is an adaptive feature of frontally oriented eyes and therefore having binocular vision. Some animals, with laterally positioned eyes, have little binocular vision, so there is a more complete crossover of visual signals. The signals are passed on to the lateral geniculate body, in turn giving them to the occipital cortex (the outer matter of the rear brain).[2]

Optic chiasm in cats

In Siamese cats with certain genotypes of the albino gene, this wiring is disrupted, with less of the nerve-crossing than is normal, as a number of scholars have reported.[3] To compensate for lack of crossing in their brains, they cross their eyes (strabismus).[4]

This is also seen in albino tigers, as Guillery & Kaas report.[5]

Additional images

See also


  1. ^ Colman, Andrew M. (2006). Oxford Dictionary of Psychology (2nd ed.). Oxford University Press. p. 530. ISBN 0198610351 
  2. ^ "eye, human." Encyclopædia Britannica from Encyclopædia Britannica 2006 Ultimate Reference Suite DVD 2009
  3. ^ OMIA "Coat colour, albinism. Phenotype in cat (Felis catus).". OMIA. http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=omia&dopt=Detailed&list_uids=418 OMIA. Retrieved 2009-09-26. 
  4. ^ Guillery RW, Kaas JH (June 1973). "Genetic abnormality of the visual pathways in a "white" tiger". Science 180 (4092): 1287–9. doi:10.1126/science.180.4092.1287. PMID 4707916. http://www.sciencemag.org/cgi/pmidlookup?view=long&pmid=4707916. 
  5. ^ Guillery RW (May 1974). "Visual pathways in albinos". Sci. Am. 230 (5): 44–54. doi:10.1038/scientificamerican0574-44. PMID 4822986. 

External links

Wikimedia Foundation. 2010.

Игры ⚽ Поможем написать курсовую

Look at other dictionaries:

  • optic chiasm — noun the crossing of the optic nerves from the two eyes at the base of the brain • Syn: ↑optic chiasma, ↑chiasma opticum • Hypernyms: ↑chiasma, ↑chiasm, ↑decussation * * * noun see optic chia …   Useful english dictionary

  • optic chiasm — optic commissure the X shaped structure formed by the two optic nerves, which pass backwards from the eyeballs to meet in the midline beneath the brain, near the pituitary gland (see illustration). Nerve fibres from the nasal side of the retina… …   The new mediacal dictionary

  • optic chiasm — noun The part of the brain where the optic nerves partially cross. Syn: optic chiasma …   Wiktionary

  • optic chiasm — noun see optic chiasma …   New Collegiate Dictionary

  • optic chiasm — chiasma opticum …   Medical dictionary

  • optic commissure — optic chiasm …   The new mediacal dictionary

  • optic chiasma — n the X shaped partial decussation on the undersurface of the hypothalamus through which the optic nerves are continuous with the brain called also optic chiasm * * * the X shaped structure formed by the two optic nerves, which pass backwards… …   Medical dictionary

  • Chiasm — may refer to: Chiasm (musical project), an electronic music project by Emileigh Rohn Optic chiasm, the part of the brain where the optic nerves partially cross Chiasma (genetics), the point where two chromatids are intertwined (interwoven) in a… …   Wikipedia

  • optic glioma — optic nerve glioma, optic pathway glioma a slow growing glioma of the optic nerve or optic chiasm heralded by loss of vision, often with secondary strabismus, followed by proptosis and loss of eye movement …   Medical dictionary

  • Optic nerve — This article is about the anatomical structure. For the comic book series, see Optic Nerve (comic). For the album about David Wojnarowicz, see Optic Nerve (CD ROM). Nerve: Optic Nerve The left optic nerve and the optic tracts …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”