Skip to Main Content

We have a new app!

Take the Access library with you wherever you go—easy access to books, videos, images, podcasts, personalized features, and more.

Download the Access App here: iOS and Android


(tră-kō′mă-tŭs) Pert. to trachoma.


(trā″kĭ-krō-măt′ĭk) [Gr. trachys, rough, + chroma, color] Pert. to a nucleus with very deeply staining chromatin.


(trās′ing) 1. A graphic record of some event that changes with time such as respiratory movements or electrical activity of the heart or brain. 2. In dentistry, a graphic display of movements of the mandible. 3. In public health, the identification of those people who may be susceptible to a disease.


(trak) 1. The path or course of a penetrating injury. 2. A treatment regimen or protocol.


(trăk′ĭng) [Fr. trac] 1. Movement in response to a stimulus, e.g., the movement of the eyes. 2. Assigning trainees to a particular course of study.


(trakt) [L. tractus, extent] 1. A pathway, course, or channel. 2. A bundle of parallel axons in the central nervous system (CNS) that runs along a stereotyped course from a common originating area to a common termination area. 3. A group of organs or parts that form a continuous pathway.

alimentary t. Digestive t.

anterior spinocerebellar t. Ventral spinocerebellar t.

ascending t. An axon tract running rostrally in the spinal cord or brain, often a sensory pathway.

biliary t. The organs and ducts through which bile travels on its way to the duodenum. These are the bile canaliculi, right and left hepatic ducts, common hepatic duct, gallbladder, cystic duct, bile duct, and hepatopancreatic ampulla. SEE: bile ducts; gallbladder; liver.

central tegmental t. An axon tract connecting the subthalamus and the midbrain reticular formation with the inferior olivary nucleus.

corticospinal t. An axon tract from the motor cortex that travels into the spinal cord, synapsing at all levels. Axons of the corticospinal tract first converge into a bundle in the posterior limb of the internal capsule and continue as a compact bundle through the cerebral peduncle. In the pons, the corticospinal tract separates into several bundles that converge more caudally in the hindbrain as the pyramid. In the caudal hindbrain, the corticospinal tract crosses the midline in the pyramidal decussation and continues down the spinal cord as the lateral corticospinal tract.

descending t. Any axon tract running caudally in the spinal cord or brain, often a motor pathway.

digestive t. The continuous set of tubes that move food from the mouth to the anus. SYN: alimentary t.

dorsal spinocerebellar t. An ipsilateral (uncrossed) axonal tract originating throughout the posterior thoracic nucleus of the spinal cord. The tract runs in the lateral funiculus of the spinal cord and ...

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.