Table 5.

Characteristics of Ascending Pain Pathways

	Lateral Spinothalamic Tract	Medial Spinothalamic Tract	Spinoreticular Tract
Origin	Neurons in lamina I and V	Neurons in lamina II and IV, VIII	Deep gray matter and lamina V
Second Order Neurons	Anterior white commissure	Anterior white commissure	Anterior lamina VII and VIII and posterior gray horns lamina V
Third Order Neurons	Ventral posterior lateral (VPL) thalamic nucleus, ventral posterior inferior (VPI) nucleus and to post-central gyrus	Medial thalamic nuclei, periaqueductal gray matter (PAG), somatosensory cortex and limbic centers	Thalamus and hypothalamus via brainstem reticular formation and limbic centers
Structure	Neospinothalamic tract with somatotopic organization (caudal elements lateral, rostral elements medial)	Paleospinothalamic tract, little somatotopic organization	Phylogenetically ancient with little somatotopic organization
Function	Sensory discriminative (localization) aspect of pain	Autonomic, affective, motivational components of pain	Perception of diffuse, emotionally disturbing pain Alertness and arousal of pain