Spina bifida results from nonfusion of which vertebral arches and defect in which closure, leading to protrusion of what?

• A. Anterior; Neural plate closure; Cerebrospinal fluid
• B. Posterior; Neural tube closure; Meninges/spinal cord
• C. Lateral; Spinal canal closure; Nerves
• D. Superior; Spinal cord closure; Brain tissue

Answer: (B)

Spina bifida is a caudal neural tube defect where the posterior parts of the spine fail to fuse. This happens because the neural tube does not close properly at the end of the neurulation process (the posterior neuropore), and the corresponding posterior vertebral arches fail to fuse. The result is a sac that protrudes through the defect containing the meninges and the spinal cord, which is the myelomeningocele form of spina bifida. The idea is that the defect is in the back part of the spine (posterior elements) and the neural tube closure failure is in the caudal region, leading to herniation of the meninges and spinal cord.