In embryology, which germ layer forms the outer skin and nervous system?

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

Answer: (C)

During gastrulation, three primary germ layers form. The outer layer is responsible for tissues at the body’s surface and the nervous system. This layer gives rise to the epidermis, which is the outer skin, and to the entire nervous system, including the brain and spinal cord, as well as neural crest derivatives. The other layers have different roles: the endoderm lines the gut and forms associated organs, while the mesoderm develops structures like muscle, bone, and the circulatory system. Epithelium is a tissue type rather than a germ layer, so it isn’t the defining term for the origin of both outer skin and nervous system.