nucleus proprius of spinal cord nucleus proprius of spinal cord the nucleus proprius is a layer of the spinal cord adjacent to the substantia gelatinosa. the 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 and iv make up the nucleus proprius. nucleus proprius of spinal cordmedulla spinalis - substantia griseadetailsidentifierslatinnucleus proprius medullae spinalis; laminae spinales iii et ivneuronames1633ta98a14.1.02.121ta26068fma73906anatomical terminology the nucleus proprius (np), along with the substantia gelatinosa of rolando are involved in sensing pain and temperature.