Central Parts of the Somatosensory System

Abstract Chapter 14 discusses neurons and pathways in the central nervous system that process somatosensory information. Somatosensory pathways consist of a chain of three neurons from the receptors to the cerebral cortex. Thick dorsal root fibers continue rostrally in the dorsal columns to end in the dorsal column nuclei. The next link forms the medial lemniscus that ends in the thalamus on the opposite side. From the thalamus, axons pass to the primary somatosensory cortex (SI). This pathway is important for discriminatory sensation. Signals conveyed in the thin dorsal root fibers are transmitted centrally in the spinothalamic tract, which is important for nociception. In the SI, signals from the body ends somatotopically, with signals from the face ending most laterally. In addition, the spinothalamic tract sends signals to other parts of the cortex such as the insula. Further analysis and integration with other sensory modalities occur in the posterior parietal cortex.