Postcentral Gyrus

The postcentral gyrus, or postcentral convolution, is a strip of cortical structure which lies just behind the central sulcus, running down adjacently and parallel to it. Bounded in back by the interparietal sulcus, the postcentral gyrus is located in the parietal lobe of the cerebral cortex. It is the seat of the processing center of somatosensory system, which is a sensory region of the brain.

Damage to the postcentral gyrus can cause agraphesthesia (disorientation in cutaneous space), astereognosia, loss of vibration, proprioception and fine touch (because the third-order neuron of the medial-lemniscal pathway cannot synapse in the cortex); and, if it affects the non-dominant hemisphere, it can also produce hemispatial neglect. It could also reduce nociception, thermoception and crude touch.

Postcentral gyrus

Decussation of the Pyramids

The decussation of the pyramids, or motor decussation, is the crossing over of cortical motor nerve fibers of the pyramidal tracts at the lower end of the medulla oblongata. About three-fifths of these pyramidal fibers leave the pyramids in successive bundles, and cross over to the opposite side in the anterior median fissure of the medulla oblongata, forming what is known as the pyramidal decussation. As a result, each of the anterior funiculus in the spinal cord is composed of motor fibers that originally come from the opposite side. The two pyramids consist of motor fibers which goes from the cerebral cortex to the medulla oblongata (via cerebral peduncles and pons) and to medulla spinalis, corticobulbar and corticospinal fibers. The word "decussation" means crossing, an X-shape crossing.

Decussation of the pyramids

Cross Section of Decussation of the Pyramids