Vessels and Nerves: Weeks 8.5 - 14

Nerves become functional

Human embryos respond to external sensory stimuli on the face as early as 8.5 weeks of gestation. Sensory receptors on the palms and soles become functional within the next two or three weeks, and by the end of the 14th week of gestation, the entire integument is wired.

Dermal nerve fiber

This thin-section light micrograph shows a well-developed periderm at the top and an epidermis with two cell layers in most places. The vascular elements in the dermis are easily identified by the presence of red blood cells in the lumen. These vascular elements will eventually demarcate the papillary and reticular dermis. The arrow indicates a dermal nerve fiber developing in parallel with the blood vessels.