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In mammals and birds and other vertebrates with frontal eyes, the optic nerves do blend in the optic chiasm, and only part of the nerve fibres cross the midline. [5] The drawings of Cajal suggest that the axons of the optic nerve may branch in the optic chiasm, and thus give off a branch both in the ipsi- and contralateral optic tract. [ 5 ]
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).
The Robo proteins are critical regulators of midline crossing across species. In Drosophila embryos, Robo1 and Robo2 are required to keep ipsilaterally projecting axons from inappropriately crossing the midline, and to prevent contralateral axons from remaining stuck at the midline. Robo3, while it also binds Slit, does not appear to play a ...
Midline shift is a shift of the brain past its center line. [1] The sign may be evident on neuroimaging such as CT scanning . [ 1 ] The sign is considered ominous because it is commonly associated with a distortion of the brain stem that can cause serious dysfunction evidenced by abnormal posturing and failure of the pupils to constrict in ...
Before crossing (ipsilaterally), the growth cone must navigate toward and be attracted to the midline. However, after crossing (contralaterally), the same growth cone must become repelled or lose attraction to the midline and reinterpret the environment to locate the correct target tissue.
The lateral corticospinal tract neurons cross the midline at the level of the medulla oblongata, and controls the limbs and digits. [1] [3] The lateral tract forms about 90% of connections in the corticospinal tract; [2] the vast majority cross over in the medulla, while the rest (about 2-3%) remain ipsilateral. The anterior corticospinal tract ...
Coronal cross-section of brain showing the corpus callosum at ... is a tract that connects the two temporal lobes of the cerebral hemispheres across the midline, ...
Decussation is used in biological contexts to describe a crossing (due to the shape of the Roman numeral for ten, an uppercase 'X' , from Latin decem 'ten' and as 'as'). In Latin anatomical terms, the form decussatio is used, e.g. decussatio pyramidum. Similarly, the anatomical term chiasma is named after the Greek uppercase 'Χ' .