Brain, nerve cells and spinal cord or the Central nervous system develops from embryonic

The correct option is ectoderm.

Step-by-Step Explanation:

During the early stages of embryonic development in animals, the blastula reorganizes into a multilayered structure known as the gastrula through a process called gastrulation. This process establishes three primary germ layers: the ectoderm (outer layer), the mesoderm (middle layer), and the endoderm (inner layer). Each germ layer is responsible for giving rise to specific tissues and organs in the developing fetus.

The nervous system, which includes the brain, spinal cord, and peripheral nerves, originates from the outermost germ layer, the ectoderm. A specialized region of the ectoderm called the neural ectoderm (or neuroectoderm) undergoes a folding process called neurulation to form the neural tube and neural crest. The neural tube subsequently differentiates into the central nervous system (comprising the brain and spinal cord), while neural crest cells give rise to the peripheral nervous system and nerve cells.

For context, the other germ layers develop into different structures:
- The mesoderm gives rise to muscles, bones, the circulatory system, and connective tissues.
- The endoderm forms the lining of the digestive tract and respiratory system, as well as associated organs like the liver and pancreas.

Therefore, the brain, nerve cells, and spinal cord develop directly from the ectoderm.