A neural tube is not an actual backbone, but is something close to it, and is a precursor to lots of things besides just the backbone / spinal cord. The neural tube is an actual tube that forms along the kid's back. It starts out looking like a ditch. It is a channel, and has little hills on both sides. The channel will become the neural tube, and the little hills are collectively called the neural crest. The neural tube is a by-product of coordinated cell division and gene regulation in the neural crest cells, which are very important.
The neural crest cells are characterized by their location alongside the neural tube and their gene expression, but other than that they look pretty much like all the other cells in the embryo (while they are next to the neural tube and still in the neural crest). However, this does not lost long. Shortly after they have formed, they actually leave the neural crest and migrate throughout the entire embryo. They move the way that amoebas do (our cells regularly migrate around our bodies using this mechanism of locomotion that was inherited from our single-celled ancestors), and slither around the embryo until they arrive at a pre-specified location. Once they get to their designated spot on the embryo, they begin to divide and differentiate, and produce all sorts of things like neurons, skin cells, cartilage and bones within the face.
You can see the neural tube in this preserved human embryo (from here):
The neural crest and neural tube are only formed in vertebrates, and are a distinguishing features of our group. All animals that have a backbone also produce a neural tube and neural crest, and it was a key evolutionary innovation that led to the origin of chordates (animals with backbones). Oscar our dog and the birds outside had a neural tube when they were an embryo. No ones knows what the first animals that had backbones may have looked like, but the closest thing that is still around today is this little guy.
This is an animal from the genus Amphioxus. Early development of animals like Amphioxus (prior to the development of a notochord) is essentially identical to development in all of us and our kid. Eventually, animals like Amphioxus will form something very similar to the backbone that you find in us, but it really is not the same. In either case, the common ancestor that gave rise to all animals with backbones (including our kid) is believed to have looked something like Amphioxus. Could be completely wrong, but that is what the fossils say for now. It is so cool!!!
So yeah! We might have a neural tube! Tomorrow when we see the ultrasound we will know for sure. Until then, we'll just be happy that Becka has the ability to produce a full-on vertebrate. All this stuff is going on right now under her skin. So cool. Word.
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