Section of themedulla oblongata at the level of the decussation of the pyramids
Decussation is used in biological contexts to describe a crossing (due to the shape of theRoman numeral for ten, an uppercase 'X' (decussis), from Latin decem'ten' and as'as'). In Latinanatomical terms, the formdecussatio is used, e.g.decussatio pyramidum.
Similarly, the anatomical termchiasma is named after the Greek uppercase 'Χ' (chi). Whereas a decussation refers to a crossing within thecentral nervous system, various kinds of crossings in theperipheral nervous system are called chiasma.
Examples include:
In thebrain, where nerve fibers obliquely cross from one lateral side of the brain to the other, that is to say they cross at a level other than their origin. See for examplesdecussation of pyramids andsensory decussation. Inneuroanatomy, the termchiasma is reserved for crossing of- or within nerves such as in theoptic chiasm.
Inbotanicalleaf taxology, the worddecussate describes anopposite pattern of leaves which has successive pairs at right angles to each other (i.e. rotated 90 degrees along the stem when viewed from above). In effect, successive pairs of leaves cross each other.Basil is a classic example of a decussate leaf pattern.Decussatephyllotaxis ofCrassula rupestris
Intooth enamel, where bundles ofrods cross each other as they travel from the enamel-dentine junction to the outer enamel surface, or near to it.
Intaxonomic description where decussate markings or structures occur, names such asdecussatus ordecussata or otherwise in part containing "decuss..." are common, especially in thespecific epithet.[1]
The origin of thecontralateral organization, the optic chiasm and the major decussations on the nervous system ofvertebrates has been a long standing puzzle to scientists.[2] The visual map theory ofRamón y Cajal has long been popular[3][4] but has been criticized for its logical inconsistence.[5] More recently, it has been proposed that the decussations are caused by anaxial twist by which the anterior head, along with theforebrain, is turned by 180° with respect to the rest of the body.[6][7]
^Ramón y Cajal, Santiago (1898). "Estructura del quiasma óptico y teoría general de los entrecruzamientos de las vías nerviosas. (Structure of the Chiasma opticum and general theory of the crossing of nerve tracks)" [Die Structur des Chiasma opticum nebst einer allgemeine Theorie der Kreuzung der Nervenbahnen (German, 1899, Verlag Joh. A. Barth)].Rev. Trim. Micrográfica (in Spanish).3:15–65.
.jpg)
Media related toDecussation at Wikimedia Commons