somatosensory

Somatosensory refers to the sensory nervous system's reception and processing of information from the body and its interactions with the environment. It includes sensations such as touch, pressure, itch, temperature, pain, proprioception, and body position, arising from receptors in the skin, muscles, tendons, joints, and viscera. Transduction converts stimuli into neural signals that travel toward the central nervous system for interpretation and action.

Modalities are mediated by distinct receptor types. Mechanoreceptors detect tactile stimuli, pressure, and vibration; proprioceptors sense limb position and movement; nociceptors convey pain; thermoreceptors encode temperature. Some receptors contribute to itch, while others respond to chemical signals. The same peripheral inputs can be processed by multiple pathways, leading to rapid, parallel signaling to the brain.

First-order neurons reside in dorsal root or cranial ganglia and project to the spinal cord or brainstem. Touch and proprioception from the body travel via the dorsal columns to the nucleus gracilis or nucleus cuneatus, then to the ventral posterior lateral nucleus of the thalamus. Pain and temperature use the spinothalamic tract to the thalamus. The face uses the trigeminal pathway to thalamic nuclei and to the primary somatosensory cortex (S1).

From thalamic and cortical stations, secondary areas such as S2 and parietal regions integrate tactile information with motor control, attention, and multisensory perception. The somatosensory system is plastic: after injury or training, cortical representations can reorganize, and somatic sensations may be altered, as in numbness, paresthesias, allodynia, or phantom limb phenomena.