The Somatic

Sensory Cortex

      AREAS WITHIN THE NEOCORTEX, to which sensory signals are projected, are generally referred to as the Somatosensory Cortex.   In man, these areas lie mainly in the anterior portion of the Parietal lobes.   Two distinct and separate areas are known to receive direct afferent nerve fibers from the relay on nuclei of the Thalamus;  called Somatic Sensory Area I (SSA-I) and Somatic Sensory Area II (SSA-II).   SSA-I lies in the post-central gyrus of the human Neocortex (in Brodmann's areas 3, 1, and 2 immediatily behind the central sulcus).

      The Somatic Sensory System has at least 20 different types of non-neural receptors, each transducing a different form of energy.   It is Proprioceptive, meaning it provides information about the relative position of body segments to one another and the position of the body in space.   It is also, Interoceptive, meaning it records internal bodily events such as blood pressure.   The receptor surface of the Somatic Sensory System is much larger than any other system, because there are receptors in all of the body tissues, except the brain itself.

      The basic organization of these receptors however, is the same as those found in vision and audition, because the membrane potential of each is altered by a particular form of energy, and because each has its own receptive field, which is an area of body tissue.   Receptors are different in each sensory system, and therefore the sensory stimulation each are capable of detecting is different.   The Somatic Sensory System monitors the entire body, except the brain itself!