All of the structures of the central nervous system originate from the __________.

• A. neural crest
• B. neural tube
• C. somites
• D. notochord

Answer: (B)

Verified step by step guidance

1. Understand the question: The problem is asking about the origin of all structures in the central nervous system (CNS). The CNS includes the brain and spinal cord, so we need to identify the embryonic structure that gives rise to these components.
2. Review the options provided: The options are 'neural crest,' 'neural tube,' 'somites,' and 'notochord.' Each of these structures plays a role in embryonic development, but only one is directly responsible for forming the CNS.
3. Clarify the role of each option: The 'neural crest' gives rise to peripheral nervous system structures, such as sensory neurons and autonomic ganglia. The 'somites' form skeletal muscles, vertebrae, and dermis. The 'notochord' is a signaling structure that helps pattern the surrounding tissues but does not directly form the CNS. The 'neural tube,' however, is the embryonic structure that develops into the brain and spinal cord.
4. Identify the correct answer: Based on the roles of these structures, the 'neural tube' is the correct answer because it is the precursor to all CNS structures.
5. Conclude the reasoning: The central nervous system originates from the neural tube, which forms during neurulation in early embryonic development. This process involves the folding of the neural plate into a tube-like structure, which later differentiates into the brain and spinal cord.