part of trigeminal nerve trigeminal nucleus BTO:0001074 BrendaTissueOBO One of the nuclei of the trigeminal nerve, consisting of a slender column of cells in the lateral central gray matter of the superior part of the fourth ventral and cerebral aqueduct. It is the only central nervous system site of primary sensory neurons; its cells resemble posterior root ganglion cells. The peripheral processes of the cells, which form the mesencephalic tract, carry proprioceptive impulses; the central processes have widespread cerebellar and brain stem connections, including the motor nucleus of the trigeminal nerve. mesencephalic nucleus of trigeminal nerve nucleus mesencephalicus nervi trigemini nucleus mesencephalicus trigeminalis nucleus tractus mesencephali nervi trigeminalis