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]

Pathways

Specifically, in the optic chiasm, the nerves connected to the right eye that attend to the left temporal visual field (located in the right retina) remain on the right (ipsilateral) side of the brain, and the nerves from the left eye that attend to the right temporal visual field (located in the left retina) remain on the left (ipsilateral) half of the brain.

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.

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. ^[2] To compensate for lack of crossing in their brains, they cross their eyes (strabismus). ^[3]

This is also seen in albino tigers, as Guillery & Kaas report.^[4]

Additional images

Mesal aspect of a brain sectioned in the median sagittal plane.	Median sagittal section of brain.	Scheme showing central connections of the optic nerves and optic tracts.	Base of brain.
Coronal section of brain through anterior commissure.	The fornix and corpus callosum from below.	Diagram showing the positions of the three principal subarachnoid cisternæ.	The left optic nerve and the optic tracts.
The hypophysis cerebri in position. Shown in sagittal section.	Median sagittal through the hypophysis of an adult monkey. Semidiagrammatic.	3D schematic representation of optic tracts	Human brainstem anterior view

See also

• Chiasmal syndrome

References

1. ^ Colman, Andrew M. (2006), Oxford Dictionary of Psychology (2nd ed.), Oxford University Press, pp. 530 
2. ^ "OMIA Coat colour, albinism. Phenotype in cat (Felis catus)." (in English). OMIA. http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=omia&dopt=Detailed&list_uids=418 OMIA. Retrieved 2009-09-26. 
3. ^ R. W. Guillery; J. H. Kaas. Genetic Abnormality of the Visual Pathways in a "White" Tiger. Science. 1973 Jun 22;180(92):1287-9. GS
4. ^ Guillery, R. Visual pathways in albinos. Scientific American 1974 May;230(5):44-54. PubMed

• Jeffery, Glen. Architecture of the Optic Chiasm and the Mechanisms That Sculpt Its Development Physiol Rev, Oct 2001; 81: 1393 - 1414.

External links

• Roche Lexicon - illustrated navigator, at Elsevier 13048.000-1

This neuroanatomy article is a stub. You can help Wikipedia by expanding it. v • d • e