Chapter 15: Sensory Transduction

Two major pathways are contrasted: the dorsal column–medial lemniscal system, which carries precise tactile information, vibration sense, and proprioceptive feedback essential for motor control and coordination, and the spinothalamic tract, which transmits pain and temperature sensations through a more diffuse cross-midline projection pattern. The thalamus integrates these signals and relays processed information to the primary somatosensory cortex, where body regions are represented in an organized but distortable map called the sensory homunculus. The chapter explains how receptive fields define the spatial boundaries of sensory perception and demonstrates that cortical representations are not fixed but exhibit plasticity in response to experience, injury, or learning. Pain processing receives extensive attention, including discussion of nociceptor activation, peripheral sensitization that amplifies pain signals at the tissue level, central sensitization that increases spinal cord responsiveness, and descending modulation systems originating from brainstem structures that can suppress or enhance pain transmission. Clinical applications illustrate how disruption at different levels produces distinct sensory deficits, including neuropathic pain from peripheral nerve damage, altered sensation following spinal cord injury, and sensory complications in diabetes. This integrated approach demonstrates how the somatosensory system translates physical stimuli into perception while maintaining capacity for adaptation and plasticity throughout the nervous system.