somatosensation
Summary
Somatosensation is the body's sense of touch, pressure, vibration, temperature, pain, and body position, detected by receptors in the skin, muscles, and joints. Its signals reach the somatosensory cortex in the parietal lobe, where cortical area reflects receptor density, not body size.
Detail
Meaning: Somatosensation, or the somatic senses, includes touch, pressure, vibration, temperature, pain (nociception), and proprioception and kinesthesis (the position and movement of body parts). Specialized receptors in the skin, muscles, tendons, and joints transduce stimuli into action potentials. Most pathways relay through the thalamus to the primary somatosensory cortex, in the postcentral gyrus of the parietal lobe. The sensory homunculus is the map of the body across this cortex. Lips, tongue, and fingertips get large areas because they have dense receptors and fine discrimination.
On the MCAT: A passage may show a homunculus and ask which body part has the larger cortical representation. It may describe two-point threshold testing, where the threshold is smaller on the fingertips than on the back. It may describe stimulation or damage to part of the postcentral gyrus and ask which body region loses sensation or feels a touch. Pain questions may bring in gate control theory, in which non-painful input can reduce pain signals.
Common confusion: Students mix up the postcentral gyrus (sensory, parietal lobe) with the precentral gyrus (primary motor cortex, frontal lobe). Cortical area tracks receptor density and sensitivity, not the physical size of the body part.
Sources
- Psychology (Myers)
- Sensation and Perception (Goldstein)
- Principles of Neural Science (Kandel)
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.