B.2. Pathways: (Table 10-3, Fig. 10-9) 1. Somatic sensory signals are conveyed along 2 major ascending systems in the spinal cord: • the dorsal column system (Main pathway for tactile information and limb proprioception). • the anterolateral system (Mediates pain and temperature and to a lesser extent tactile sensation). 2. These 2 ascending pathways are bilateral and symmetrical. 3. These 2 ascending pathways cross over to the opposite (contralateral) side. As a result, sensory events on one side are relayed and perceived by the cerebral hemisphere (the somatosensory cortex) on the opposite side: the dorsal column column system crosses in the medulla (part of the brain stem); the anterolateral system crosses in the spinal cord. B.3. Somatotopy: (the sensory homunculus: Fig. 10-10 The various areas of the peripheral receptive sheet are represented in the central nervous system in an orderly manner. Receptors in adjacent areas of the peripheral receptive sheet ultimately project to neurons in adjacent areas of the somatic
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