The Nucleus proprius is a layer of the spinal cord adjacent to the substantia gelatinosa. Nucleus proprius can be found in the gray matter in all levels of the spinal cord. It constitutes the first synapse of the spinothalamic tract carrying pain and temperature sensations from peripheral nerves. Cells in this nucleus project to deeper laminae of the spinal cord, to the posterior column nuclei, and to other supraspinal relay centers including the midbrain, thalamus, and hypothalamus. Rexed laminae III, IV, and V make up the nucleus proprius. Nucleus proprius (NP), along with nucleus dorsalis (ND) are involved in sensing pain and temperature.