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Optic chiasm

Structure and Development: – Optic nerves of left and right eye meet in the body midline in vertebrates. – Left optic nerve crosses over the […]

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Structure and Development:
– Optic nerves of left and right eye meet in the body midline in vertebrates.
– Left optic nerve crosses over the right one in many vertebrates.
– Optic nerves merge in the optic chiasm in mammals, birds, amphibians, and reptiles.
– Development of the optic chiasm in mammals is guided by cues like netrin and slit.
– Neuronal growth cone responds to cues inducing cytoskeleton changes.
– Majority of retinal ganglion cell (RGC) axons cross the midline at the ventral diencephalon.
– Ephrin-B2 at the chiasm midline acts as a repulsive signal for axons.

Function and Evolution:
– Crossing over at the optic chiasm enables binocular depth perception.
– Theories proposed for the function of the optic chiasm in vertebrates.
– Disrupted wiring in Siamese cats with certain genotypes of the albino gene.
– Siamese cats with disrupted wiring may compensate with strabismus.
– Function and evolution of the optic chiasm in vertebrates not fully understood.
– Axial Twist theory suggests development of the optic chiasm due to embryo twist.

History and Additional Information:
– Persian physician Esmail Jorjani possibly first identified nerve fibers crossing.
– Impact on vision from nerve fiber crossing recognized early.
– Optic chiasm’s function and evolution have been subjects of various theories.
– Siamese cats with disrupted wiring show abnormal nerve-crossing patterns.
– Various images showing the central connections of optic nerves and tracts, brain view with optic chiasm highlighted, transformations of the visual field towards the visual map on the primary visual cortex, and more.

Anatomy and Development of the Optic Chiasm:
– Optic chiasm is an X-shaped structure located at the base of the brain.
– It is formed by the crossing of optic nerve fibers.
– Damage to the optic chiasm can lead to visual field defects.
– The development of the optic chiasm is tightly regulated.
– Timing and signaling pathways play a critical role in chiasm formation.

Clinical Implications and Research:
– Abnormalities in the optic chiasm can lead to visual disturbances.
– Tumors affecting the optic chiasm can cause vision loss.
– Research on optic chiasm abnormalities has implications for understanding visual processing disorders.
– Various studies have explored the molecular mechanisms underlying optic chiasm development.
– Neuroimaging techniques have provided insights into the structure and function of the optic chiasm.

Optic chiasm (Wikipedia)

In neuroanatomy, the optic chiasm, or optic chiasma ( /ɒptɪk kæzəm/; from Greek χίασμα 'crossing', from Ancient Greek χιάζω 'to mark with an X'), is the part of the brain where the optic nerves cross. It is located at the bottom of the brain immediately inferior to the hypothalamus. The optic chiasm is found in all vertebrates, although in cyclostomes (lampreys and hagfishes), it is located within the brain.

Optic chiasm
Brain viewed from below; the front of the brain is above. Visual pathway with optic chiasm (X shape) is shown in red (image from Andreas Vesalius' Fabrica, 1543).
Optic nerves, chiasm, and optic tracts
SystemVisual system
FunctionTransmit visual information from the optic nerves to the occipital lobes of the brain
Latinchiasma opticum
NeuroLex IDbirnlex_1416
Anatomical terms of neuroanatomy

This article is about the optic chiasm of vertebrates, which is the best known nerve chiasm, but not every chiasm denotes a crossing of the body midline (e.g., in some invertebrates, see Chiasm (anatomy)). A midline crossing of nerves inside the brain is called a decussation (see Definition of types of crossings).

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