Optic chiasm
Encyclopedia
The optic chiasm or optic chiasma (Greek
, "crossing", from the Greek 'to mark with an X', after the Greek letter 'Χ
', chi) is the part of the brain
where the optic nerve
s (CN II) partially cross. The optic chiasm is located at the bottom of the brain immediately below the hypothalamus
.
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).
s with certain genotype
s 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 tiger
s, as Guillery & Kaas report.
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
, "crossing", from the Greek 'to mark with an X', after the Greek letter 'Χ
Chi (letter)
Chi is the 22nd letter of the Greek alphabet, pronounced as in English.-Greek:-Ancient Greek:Its value in Ancient Greek was an aspirated velar stop .-Koine Greek:...
', chi) is the part of the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
where the optic nerve
Optic nerve
The optic nerve, also called cranial nerve 2, transmits visual information from the retina to the brain. Derived from the embryonic retinal ganglion cell, a diverticulum located in the diencephalon, the optic nerve doesn't regenerate after transection.-Anatomy:The optic nerve is the second of...
s (CN II) partially cross. The optic chiasm is located at the bottom of the brain immediately below the hypothalamus
Hypothalamus
The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
.
Pathways
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 systemVisual system
The visual system is the part of the central nervous system which enables organisms to process visual detail, as well as enabling several non-image forming photoresponse functions. It interprets information from visible light to build a representation of the surrounding world...
in the brain, and vice versa. This is linked to skin sensation which reaches the opposite side of the body, after reaching the diencephalon
Diencephalon
The diencephalon is the region of the vertebrate neural tube which gives rise to posterior forebrain structures. In development, the forebrain develops from the prosencephalon, the most anterior vesicle of the neural tube which later forms both the diencephalon and the...
(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).
Optic chiasm in cats
In Siamese catSiamese (cat)
The Siamese is one of the first distinctly recognized breeds of Oriental cat. The origins of the breed are unknown, but it is believed to be from Thailand. In Thailand, where they are one of several native breeds, they are called Wichian Mat...
s with certain genotype
Genotype
The genotype is the genetic makeup of a cell, an organism, or an individual usually with reference to a specific character under consideration...
s 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
Strabismus
Strabismus is a condition in which the eyes are not properly aligned with each other. It typically involves a lack of coordination between the extraocular muscles, which prevents bringing the gaze of each eye to the same point in space and preventing proper binocular vision, which may adversely...
).
This is also seen in albino tiger
Tiger
The tiger is the largest cat species, reaching a total body length of up to and weighing up to . Their most recognizable feature is a pattern of dark vertical stripes on reddish-orange fur with lighter underparts...
s, as Guillery & Kaas report.