somatosensory cortex

Meaning: The somatosensory cortex is the strip of parietal-lobe cortex along the postcentral gyrus, just behind the central sulcus. It receives touch, pressure, vibration, temperature, pain, and body-position input, relayed mostly through the thalamus. It is organized as a map of the body (the sensory homunculus), and the amount of cortex given to each body part reflects its receptor density and sensitivity, not its physical size. Input from one side of the body goes mainly to the opposite hemisphere.

On the MCAT: Expect questions that ask you to locate it, to read a homunculus figure and pick the body part with the finest touch discrimination (lips, fingers, tongue), or to predict the effect of stimulating or damaging one spot, such as tingling in the right hand when the left hemisphere is stimulated. Passages may also describe cortical remapping after amputation or intensive practice, where neighboring regions expand into the area.

Common confusion: Students swap the postcentral gyrus (sensory, parietal lobe) with the precentral gyrus (primary motor cortex, frontal lobe). The sensory strip lies behind the central sulcus, the motor strip in front of it. Students also assume the homunculus is drawn to body size, but it is distorted by sensitivity, so the back is small despite its large surface area.