tractus

Tractus is the Latin term for a route or course and is used in anatomy to refer to a bundle of axons within the central nervous system (CNS) that connects different brain regions or carries information between the brain and the spinal cord. In English, the corresponding term is tract; the term tractus is commonly found in classical anatomical texts and in Latinized nomenclature.

In the CNS, tracts are components of white matter, consisting of parallel fibers that share a common origin and termination. They form major communication channels and are typically classified as ascending (sensory) or descending (motor) pathways. Names usually reflect their origin and destination (for example, corticospinal tract from cerebral cortex to the spinal cord) or their function (such as spinothalamic tract carrying pain and temperature to the thalamus). Other well-known tracts include the dorsal column–medial lemniscus pathway for fine touch and proprioception, the trigeminothalamic tract for somatosensation from the face, and the vestibulospinal, reticulospinal, rubrospinal, and tectospinal tracts that influence posture and movement. Some are paired with other terms, such as the pyramidal tract (corticospinal tract) or lemniscal pathways.

Decussation patterns vary; many tracts cross to the opposite side at different levels of the CNS, contributing to contralateral or bilateral control of functions. The term tractus is sometimes used in reference to non-neural routes as well, notably in phrases such as tractus digestorius (gastrointestinal tract) or tractus urinarius (urinary tract), reflecting a broader Latin sense of a tract or route.

Overall, tractus denotes a routed set of fibers or passages in biology, with emphasis on connectivity within the CNS or organ systems.