Optic chiasm

Brain: Optic chiasm
Visual pathway with optic chiasm (X shape outlined, red) (1543 image from Andreas Vesalius' Fabrica)
[[Image:|250px|center|]]
Latin	chiasma opticum
Gray's	subject #197 883
Part of
Components
Artery
Vein
BrainInfo/UW	-
MeSH	A08.800.800.120.680.600

The optic chiasm (Greek χίασμα, "crossing", from the Greek χλαζειν 'to mark with an X', after the Greek letter chi) is the part of the brain where the optic nerves partially cross.

Pathways

Specifically, in the optic chiasm, the nerves connected to the right eye that attend to the right temporal visual field (located in the right retina) cross to the left half of the brain, while the nerves from the left eye that attend to the left temporal visual field (located in the left retina) cross to the right 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. To compensate for lack of crossing in their brains, they cross their eyes (strabismus).

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

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 2 description.JPG

Human brainstem anterior view

See also

• Chiasmal syndrome

References

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

External links

Nerves of head and neck: the cranial nerves

I-IV: olfactory - optic - oculomotor - trochlear

V: trigeminal: trigeminal ganglion
V1: ophthalmic: lacrimal - frontal (supratrochlear, supraorbital) - nasociliary (long root of ciliary, long ciliary, infratrochlear, posterior ethmoidal, anterior ethmoidal) - ciliary ganglion (short ciliary)
V2: maxillary: middle meningeal - in the pterygopalatine fossa (zygomatic, zygomaticotemporal, zygomaticofacial, sphenopalatine, posterior superior alveolar)
in the infraorbital canal/infraorbital nerve (middle superior alveolar, anterior superior alveolar)
on the face (inferior palpebral, external nasal, superior labial, infraorbital plexus) - pterygopalatine ganglion (deep petrosal, nerve of pterygoid canal)
branches of distribution (palatine, nasopalatine, pharyngeal)
V3: mandibular: nervus spinosus - medial pterygoid - anterior (masseteric, deep temporal, buccal, lateral pterygoid)
posterior (auriculotemporal, lingual, inferior alveolar, mylohyoid, mental) - otic ganglion - submandibular ganglion

VI: abducens

VII: facial: nervus intermedius - geniculate - inside facial canal (greater petrosal, nerve to the stapedius, chorda tympani)
at exit from stylomastoid foramen (posterior auricular, digastric - stylohyoid)
on face (temporal, zygomatic, buccal, mandibular, cervical)

VIII: vestibulocochlear: cochlear (striae medullares, lateral lemniscus) - vestibular

IX: glossopharyngeal: fasciculus solitarius - nucleus ambiguus - ganglia (superior, petrous) - tympanic - carotid sinus

X: vagus: ganglia (jugular, nodose) - Alderman's nerve - in the neck (pharyngeal branch, superior laryngeal ext and int, recurrent laryngeal)
in the thorax (pulmonary branches, esophageal plexus) - in the abdomen (gastric plexuses, celiac plexus, gastric plexus)

XI: accessory XII: hypoglossal