Which germ layer forms the skin and nervous system?

• A. Mesoderm
• B. Ectoderm
• C. Endoderm
• D. Tectoderm

Answer: (B)

The ectoderm is the germ layer that forms both the skin and the nervous system. Early in development, the outermost layer (the ectoderm) gives rise to the epidermis of the skin as well as all neural tissue—the brain, spinal cord, and peripheral nerves—through processes that create the neural plate, neural tube, and neural crest. The mesoderm forms things like muscle, bone, and the circulatory system, while the endoderm lines the gut and its associated organs. A term like tectoderm isn’t used in standard embryology, so it doesn’t represent a germ layer.