Editing Neurulation (section)

==Secondary neurulation==
Primary neurulation develops into secondary neurulation when the caudal neuropore undergoes final closure. The cavity of the spinal cord extends into the neural cord.<ref>{{Cite journal|url=https://onlinelibrary.wiley.com/doi/abs/10.1002/tera.1420400111|doi = 10.1002/tera.1420400111|title = Developmental stages in human embryos. R. O'Rahilly and F. Müller (Eds), Carnegie Institution of Washington, Washington, DC, 1987, 306 pp., $52|year = 1989|last1 = Shepard|first1 = Thomas H.|journal = Teratology|volume = 40|page = 85|url-access = subscription}}</ref>  In secondary neurulation, the neural ectoderm and some cells from the endoderm form the medullary cord. The medullary cord condenses, separates and then forms cavities.<ref>[https://www.ncbi.nlm.nih.gov/books/NBK10080/ Formation of the Neural Tube] Developmental Biology NCBI Bookshelf</ref> These cavities then merge to form a single tube. Secondary neurulation occurs in the posterior section of most animals but it is better expressed in birds. Tubes from both primary and secondary neurulation eventually connect at around the sixth week of development.<ref>{{cite journal|last=Shimokita|first=E|author2=Takahashi, Y |title=Secondary neurulation: Fate-mapping and gene manipulation of the neural tube in tailbud.|journal=Development, Growth & Differentiation|date=April 2011|volume=53|issue=3|pages=401–10|pmid=21492152|doi=10.1111/j.1440-169X.2011.01260.x|doi-access=free}}</ref>

In humans, the mechanisms of secondary neurulation plays an important role given its impact on the proper formation of the human posterior spinal cord. Errors at any point in the process can yield problems. For example, retained medullary cord occurs due to a partial or complete arrest of secondary neurulation that creates a non-functional portion on the vestigial end.<ref>{{cite journal |last1=Pang |first1=Dachling |last2=Zovickian |first2=John |date=2011 |title="Retained medullary cord in humans: late arrest of secondary neurulation" |url=https://pubmed.ncbi.nlm.nih.gov/21336222/ |journal=Neurosurgery |volume=68 |issue=6 |pages=1500–19 |doi=10.1227/NEU.0b013e31820ee282 |pmid=21336222 |s2cid=25638763 |access-date=2020-11-19}}</ref>