Prenatal development of the human chief sensory trigeminal nucleus.

Abstract

AbstractThe development of the chief (main or principal) sensory nucleus of V was studied in 27 human embryos and fetuses, 7 to 30 weeks of menstrual age (19 to 261 mm CR length). Nissl and protargol silver preparations were used.The chief sensory nucleus develops by the migration of neuroblasts from the neuroepithelium lateral to the sulcus limitans. Migrations occur cAUdally at levels of the entering sensory root fibers and posterior trigeminal nucleus in the 18 mm, 7‐week embryo and later (24 mm, 8 weeks) at levels rostral to the motor nucleus of V. Cell differentiation within the nucleus progresses in a similar cAUdorostral sequence (cAUdally at 8.5 weeks, 27.4 mm and rostrally at 12.5 weeks, 65.5 mm) as well as in a dorsoventral sequence. Correlations between neuronal differentiation and functional activity indicate that the dorsal part of the chief sensory nucleus serves the maxillo‐mandibular divisions and the ventral part serves the ophthalamic division of V. In general, the ontogenetic development of the human chief sensory nucleus and the phylogenetic development of this nucleus are comparable.At 7.5 weeks (20.7 mm) a group of better differentiated cells appears cAUdally in the dorsomedial region of the primitive chief sensory nucleus (level of the posterior trigeminal nucleus). In 8.5‐week fetuses the cells of this group exhibit characteristics of functional neurons and form a distinct island. Neurons in this position remain the largest and best differentiated of those in the chief sensory nucleus throughout the fetal period studied. These large, dorsomedially located cells appear at progressively more rostral levels so that at 12.5 weeks they extend nearly to the rostral pole of the nucleus. It is suggested that these neurons constitute at least part of the supratrigeminal nucleus and that they serve as an integral part of the reflex arc concerned with mouth opening which occurs as a part of the total pattern response of the human fetus to perioral stimulation at 8.5 weeks and later with other reflex jaw muscle activity.