The spinothalamic tract.

The spinothalamic tract (STT) is made up of axons, originating from neurons in the spinal cord grey matter, which cross segmentally and then ascend to terminate in a variety of thalamic nuclei. The cells of origin of the STT are located throughout the spinal cord in three functional groups. Those located in lamina 1 of the spinal cord have small receptive fields and respond maximally to noxious peripheral stimulation. Those located in spinal cord laminae 4-6 have somewhat larger receptive fields and respond most commonly to both innocuous and noxious stimuli. The group originating in laminae 7-10 have large, frequently bilateral receptive fields and respond to a wide variety of cutaneous and deep stimuli. The largest concentration of STT neurons is found in the upper cervical spinal cord. The terminations of the STT in the thalamus include the lateral sensory thalamus, the intralaminar nuclei (primarily the centrolateral nucleus), and some of the medial nuclei (most prominently the medial dorsal nucleus). The cells located in laminae 1-6 project primarily to the lateral thalamus while the deeper STT neurons project primarily to the intralaminar and medial thalamus. An unique projection of lamina 1 cells to the nucleus submedius has been described. We hypothesize that the deep cells are related to many of the aversive aspects of pain while the more superficial STT cells are related to the sensory-discriminative aspects of pain.