Question

Which of the following is/are true with regard to neurulation? I. The neural tube differentiates from endoderm. II. The neural tube becomes the peripheral nervous system. III. Neural crest cells migrate from their original site. (A) I only (B) III only (C) Il and III only (D) I, II , and III

Short answer

The correct answer is (B) III only.

Step-by-step solution

Understand Neurulation

Neurulation is the process during embryonic development where the neural tube is formed. The neural tube ultimately becomes the central nervous system (CNS), which includes the brain and spinal cord.

Evaluate Statement I

Statement I claims that the neural tube differentiates from the endoderm. In reality, the neural tube differentiates from the ectoderm, not the endoderm. Therefore, Statement I is false.

Evaluate Statement II

Statement II claims that the neural tube becomes the peripheral nervous system (PNS). The neural tube actually forms the central nervous system, not the PNS. Therefore, Statement II is false.

Evaluate Statement III

Statement III claims that neural crest cells migrate from their original site. This is true, as neural crest cells do migrate to different parts of the embryo and differentiate into various cell types, contributing to the PNS, among other structures.

Conclusion

Based on the evaluations: Statement I is false, Statement II is false, and Statement III is true. Therefore, only Statement III is true.

Key concepts

Neural Tube

Neurulation is a crucial phase of embryonic development, where the neural tube is formed. The process begins when the ectoderm, one of the three germ layers of the early embryo, starts to thicken and forms a structure called the neural plate. Gradually, the edges of the neural plate elevate and fold towards each other, creating a groove. Eventually, these edges fuse together, forming the neural tube.

The neural tube is essential because it differentiates into the central nervous system (CNS). This includes the brain and spinal cord. Hence, the proper formation of the neural tube is vital for the correct development of these critical structures. Defects in the neurulation process can lead to severe congenital conditions such as spina bifida and anencephaly.

• Formed from ectoderm
• Develops into the central nervous system
• Key structures: brain and spinal cord

Neural Crest Cells

Neural crest cells are a unique and highly versatile group of cells that arise from the edges of the neural plate during neurulation. Once the neural tube is formed, these cells disengage from the ectoderm and begin their journey, migrating to various parts of the embryo.

The migratory nature of neural crest cells enables them to differentiate into an astonishing variety of cell types and tissues. Some of the critical contributions of neural crest cells include:

• Peripheral nervous system (PNS) development
• Formation of the adrenal medulla
• Generation of pigment cells (melanocytes)
• Development of facial cartilage and bone
• Contributions to the heart, such as cardiac septa

This remarkable multipotency is what makes neural crest cells indispensable in the formation of numerous structures in the body.

Central Nervous System (CNS)

The central nervous system (CNS) is made up of the brain and spinal cord, arising from the neural tube formed during neurulation. The CNS is the control center for the entire body, governing everything from movement and sensation to thought and emotion.

Here are some essential aspects of the CNS:

• Brain: The brain is the most complex organ and is responsible for higher functions like cognition, emotion, memory, and sensory processing. It is divided into several regions, including the cortex, cerebellum, and brainstem.
• Spinal Cord: The spinal cord serves as the main conduit for transmitting signals between the brain and the rest of the body. It also coordinates reflexes and automatic responses.
• Protection: The CNS is protected by the skull and vertebral column, as well as cerebrospinal fluid and meninges, which provide cushioning and a barrier from pathogens.

The formation and development of the CNS need to be precise, as any anomalies can result in significant neurological impacts.