Lateral spinothalamic tract

At a glance

English

Lateral spinothalamic tract

Latin (TA2)

Tractus spinothalamicus lateralis

System

Brain and spinal cord

Region

Whole body

Side

Single, on the midline

About the lateral spinothalamic tract

The lateral spinothalamic tract runs up the front half of the lateral funiculus, just outside the anterior horn. With the smaller anterior spinothalamic tract it forms the anterolateral system, also named the spinal lemniscus once it reaches the brainstem. Its job is to bring warning sensations, pain and temperature, together with itch and some crude touch, to the brain.

The first neuron sits in a dorsal root ganglion. Its peripheral branch ends as free nerve endings in skin and deeper tissues, which respond to heat, cold and chemicals released by injured tissue. Fast, thinly myelinated Aδ fibres carry sharp, well-localised pain; slow, unmyelinated C fibres carry dull, burning pain. On entering the cord the central branch runs up or down a segment or two in the posterolateral (Lissauer's) tract at the tip of the posterior horn before it ends.

The second neurons lie in the posterior horn, mainly in lamina I and in laminae IV to VI; lamina II, the substantia gelatinosa, is made largely of small interneurons that adjust the signal before it is relayed. Second-order axons cross to the other side in the anterior white commissure within about one or two segments, then ascend. In the cord the tract is laid out by body region, with sacral fibres outermost and cervical fibres innermost. It passes through the medulla, pons and midbrain to the ventral posterolateral nucleus of the thalamus, and third-order fibres pass by way of the internal capsule and the corona radiata to reach the postcentral gyrus (areas 3, 1 and 2 of Brodmann).

Some fibres branch off to the reticular formation and midbrain, forming indirect routes that raise alertness and give pain its unpleasant, emotional colour. Clinically, crossing low in the cord explains why a hemisection causes loss of pain and temperature on the opposite side below the lesion, the Brown-Séquard pattern. Surgeons once cut the tract (cordotomy) to relieve intractable pain.

Function and supply

Function

Carries pain, temperature and itch from the opposite half of the body to the thalamus and on to the somatosensory cortex, with side branches that drive arousal and the emotional response to pain.

Blood supply

Lies in the territory of the anterior spinal artery, which supplies the anterior two-thirds of the cord.