Decussare

Decussare is an Italian verb meaning to cross in a manner that forms an X or to cross from one side to the opposite along a midline. In scientific language, the term is most commonly used in anatomy and botany to describe crossing or perpendicular arrangement of structures.

In neuroanatomy, decussation refers to the crossing of nerve fibers from one side of the body to the other. Examples include the pyramidal decussation in the medulla, where most corticospinal fibers cross to control opposite limbs, and the decussation of the dorsal column fibers at the level of the medulla as internal arcuate fibers, which contributes to contralateral sensory representation. The spinothalamic tract typically decussates at the level of entry into the spinal cord, producing contralateral pain and temperature perception. The concept of decussation explains why lesions in one hemisphere can affect the opposite side of the body.

In vision, decussation occurs at the optic chiasm, where fibers from the nasal retina cross to the opposite side. This crossing contributes to binocular vision and the organization of visual pathways.

In botany, decussate describes a leaf arrangement in which opposite leaves are positioned at right angles to the next pair. This pattern, found in several plant groups, can influence growth form and leaf orientation.

The term is used across disciplines to denote crossing or alternating patterns that result in a change of side, frequently with functional or organizational significance.