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The optic chiasm is found in all vertebrates, although in cyclostomes (lampreys and hagfishes), it is located within the brain. [2] [3] 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)).
In anatomy a chiasm is the spot where two structures cross, forming an X-shape (from Greek letter χ, Chi). Examples of chiasms are: A tendinous chiasm, the spot where two tendons cross. For example, the tendon of the flexor digitorum superficialis muscle, and the tendon of the flexor digitorum longus muscle which even forms two chiasms.
In rhetoric, chiasmus (/ k aɪ ˈ æ z m ə s / ky-AZ-məs) or, less commonly, chiasm (Latin term from Greek χίασμα chiásma, "crossing", from the Greek χιάζω, chiázō, "to shape like the letter Χ"), is a "reversal of grammatical structures in successive phrases or clauses – but no repetition of words".
Chiasm (anatomy), an X-shaped structure produced by the crossing over of the fibers, with the prefix chiasm- means cross examples include: A nerval chiasm, where either two nerves cross in the body midline (e.g. Optic chiasma) A crossing of fibres inside a nerve reversing their mapping; A tendinous chiasm, the spot where two tendons cross.
An example of chiastic structure would be two ideas, A and B, together with variants A' and B', being presented as A,B,B',A'. Chiastic structures that involve more components are sometimes called "ring structures" or "ring compositions". These may be regarded as chiasmus scaled up from words and clauses to larger segments of text.
For example, a striatal afferent is an afferent originating at the striatum. An efferent nerve fiber is one that arrives at the present point. For example, a cortical efferent is a fibre coming from elsewhere, and arriving to the cortex. That is the opposite of the direction in which the nerve fibre conducts signals.
Due to these oppositely directed compensations of the anterior head and the rest of the body, the animal becomes twisted. [10] The optic tract grows from the retina to the optic tectum. Because dorsal and ventral are inverted in the anterior head region, the tracts grow at first toward the ventral side, to meet in the midline to form a chiasma.
See for examples decussation of pyramids and sensory decussation. In neuroanatomy , the term chiasma is reserved for crossing of- or within nerves such as in the optic chiasm . In botanical leaf taxology , the word decussate describes an opposite pattern of leaves which has successive pairs at right angles to each other (i.e. rotated 90 degrees ...