Neuroanatomy, Spinothalamic Tract

The spinothalamic tract (STT) is a sensory tract that carries nociceptive, temperature, crude touch, and pressure from our skin to the somatosensory area of the thalamus. It is responsible for our quick withdraw reaction to a painful stimulus such as touching the stove burner. The spinothalamic tract is composed of two adjacent pathways: anterior and lateral. The anterior spinothalamic tract carries sensory input about crude touch. The lateral spinothalamic tract carries information about pain and temperature. These two divisions of the spinothalamic tract run next to each other indistinctly. Thus, they can be considered one pathway. The spinothalamic tract is part of the anterolateral system, which also encompasses the spinoreticulothalamic tract (SRTT) and the spinotectal tract (SpTT). Three types of sensory fibers are associated with the spinothalamic tract: type III fibers, unmyelinated c-fibers, and myelinated A-delta fibers. Peripheral receptors having associations with the spinothalamic tract pathway are nociceptors, thermal receptors, and thermal nociceptors. Nociceptors are associated with A-delta and type III fibers, which are small, lightly myelinated axons for the transmission of fast, sharp pain. Thermal receptors and thermal nociceptors are associated with A-delta and C fibers, which are small, unmyelinated axons that conduction the transmission of slow-burning pain.The pathway of the spinothalamic tract to the cerebral cortex starts with the dorsal root ganglions, which are composed of pseudounipolar neurons with the peripheral (distal) and central (proximal) axonal processes. These dorsal root ganglia lie adjacent to the spinal cord and represent the first-order neuron of the spinothalamic tract pathway. The axons of the central process of the first-order neurons enter the spinal cord through the lateral dorsal root entry zone to enter the Lissauer tract and synapses with second-order neurons in the substantia gelatinosa, located in the grey matter of the spinal cord. The axons of the second-order neurons cross over the spinal cord to the opposite side two segments above the level of entry via the anterior white commissure, unlike the posterior medial lemniscus pathway, which decussates in the brainstem. The decussating second-neuron fibers enter the anterolateral portion of the spinal cord and then enter the brainstem as the spinal lemniscus. The spinothalamic tract ascends in the ventrolateral aspect of the spinal white matter over the length of the spinal cord. The anterolateral system in the rostral medulla runs between the inferior olivary nucleus and the nucleus of the spinal trigeminal tract, whereas, in the pons and midbrain, the anterolateral system runs dorsolaterally to the medial lemniscus. The spinothalamic tract of the anterolateral system terminates in the ventral posterolateral nucleus (VPL) of the thalamus, the third-order neurons of this pathway. From the thalamus, axons of VPL neurons project out of the thalamus laterally and course somatotopically through the internal capsule's posterior limb of the and terminate in the postcentral gyrus primary somatosensory. In the spinal cord, the spinothalamic tract pathway has a certain somatotopic organization. The medial part of the track receives cervical input while the lateral part receives sacral input. Other pathways, such as cortical spinal tract and posterior medial lemniscus pathway, have a reversed somatotopy in comparison to the spinothalamic tract.