Definition: a general term describing a large ascending fiber bundle in the ventral half of the lateral funiculus of the spinal cord, arising from cells in the posterior horn at all levels of the cord, which cross within their segments of origin in the white commissure. This tract, part of a larger bundle commonly called the spinal lemniscus or anterolateral tract (anterolateral system), contains spinothalamic fibers, spinoreticular fibers, spinohypothalamic fibers, spinomesencephalic fibers (as spinotectal and spinoperiaqueductal fibers), and some projections from the spinal cord to the inferior olivary complex (spinoolivary). In their contralateral ascent, the bundle is intermingled with numerous intersegmental fibers. These fibers continue from the spinal cord into the brainstem, occupying a ventrolateral position and issuing numerous fibers to the rhombencephalic and mesencephalic reticular formation (spinoreticular fibers), to the accessory olivary nuclei (spinoolivary) fibers, to the lateral part of the central gray substance of the mesencephalon (spinoperiaqueductal fibers), and to the deep and intermediate layers of the superior colliculus (spinotectal fibers); the relatively few fibers (10–20%) that remain are the spinothalamic fibers that enter the diencephalon and end in the nucleus ventralis posterior (caudal part) and intralaminar nuclei of the thalamus. In its ascent in the spinal cord, this tract was originally described as being composed of a dorsal part, the lateral spinothalamic tract, which conveys impulses associated with pain and temperature sensation, and a more ventral part, the anterior spinsothalamic tract, involved in tactile sensation. It is now known that this division is not as obvious as originally thought.
See: anterolateral system
Synonym(s): tractus spinothalamicus
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