Lateral spinothalamic tract

The lateral spinothalamic tract is a key ascending sensory pathway responsible for transmitting pain and temperature sensations. Free nerve endings in the skin and other tissues detect these stimuli, and the information is conveyed via two types of primary afferent fibers: fast-conducting A-delta fibers and slow-conducting C fibers.

These first-order neurons have their cell bodies located in the dorsal root ganglia. Their axons enter the spinal cord through the dorsal horn, specifically at the apex of the posterior gray column. Upon entry, the axons travel a short distance up and down the spinal cord, forming the posterolateral tract of Lissauer. They then synapse with second-order neurons primarily within the substantia gelatinosa of the posterior gray horn, releasing the neurotransmitter substance P.

The axons of these second-order neurons decussate (cross over) at the spinal level, traveling anteriorly through the anterior white and gray commissures to the contralateral side. They then ascend within the anterolateral white matter of the spinal cord. The fibers ascending in the lateral funiculus form the lateral spinothalamic tract, while those in the anterior funiculus constitute the anterior spinothalamic tract (carrying crude touch and pressure).

Within the spinal cord, the lateral spinothalamic tract is positioned medial to the anterior spinocerebellar tract. As it ascends through the medulla, it lies posterior to the inferior olivary nucleus. Here, it joins the anterior spinothalamic and spinotectal tracts to form the spinal lemniscus. The spinal lemniscus continues through the pons and into the midbrain tegmentum.

Finally, the second-order neurons of the lateral spinothalamic tract synapse with third-order neurons in the ventral posterolateral (VPL) nucleus of the thalamus. These third-order neurons project via thalamocortical fibers through the corona radiata to the primary somatosensory cortex (postcentral gyrus, Brodmann areas 3, 1, and 2). The somatotopic organization within this cortex results in an inverted representation of the body (the sensory homunculus), with the face and upper limbs represented laterally and the legs medially.