Ectoderm

The ectoderm is the outermost of the three primary germ layers formed during early embryogenesis. It originates from the epiblast during gastrulation and gives rise to tissues that cover the embryo and contribute to the nervous system and sensory organs, as well as some facial structures.

During development, the ectoderm differentiates into two main domains: the neuroectoderm and the surface ectoderm. The neuroectoderm forms the neural plate, which folds to become the neural tube (the precursor to the central nervous system) and gives rise to neural crest cells. Neural crest derivatives include peripheral nerves, melanocytes, facial cartilage and bone, dentin, and the adrenal medulla, among others. The surface ectoderm forms the epidermis and its appendages (hair, nails, and glands), as well as the lens of the eye and portions of the oral and nasal epithelium.

The nervous system largely derives from the neuroectoderm, with the brain and spinal cord developing from the neural tube and the retina arising from neural ectoderm. The epidermis forms a protective barrier, while neural crest derivatives contribute to many craniofacial structures and several sensory and autonomic tissues. The development of ectodermal tissues is influenced by signaling gradients, including BMP-related pathways, which help determine whether ectodermal cells adopt neural or epidermal fates.

In summary, the ectoderm provides the foundational tissues for the nervous system, skin and its derivatives, eyes, and various craniofacial structures, reflecting its essential role in embryonic development and organ formation.