In a previous article we looked at the formation of the neural tube. (If you need to, you can go back to that article and refresh your memory).

In this article, we will take a look at what happens during development after the formation of the neural tube.

In time, the neural tube will become the entire Central Nervous System!

At The Fourth Week Stage

Here is what we have at the beginning of the fourth week:

• We have the closed neural tube.
• On top of that we have some the ectoderm (this side will become the dorsal side).
• Under the closed neural tube we have some mesoderm (notochord)

As development occurs, the ectoderm and the mesoderm release different chemicals that serve as signals to the different parts of the neural tube to differentiate.

At the beginning, this difference in signaling is what “stretches” the neural tube into the shape, and a little groove appears in the middle. This little groove is called the sulcus limitans.

This sulcus limitans marks the “limit” between what we can now call:

• The alar plate at the top (the side of the neural tube that is closest to the dorsal ectoderm).
• And the basal plate underneath (the side of the neural tube that is closest to the notochord).

 College Competition Analogy

If you have a hard time understanding how something that was initially the same can give rise to different functions just by receiving different signals, you can imagine this process as something like this:

You have 2 identical twins that just graduated from high school, and they share the same knowledge and values.
However, one of them is close to a coach from UCLA, and the other one is close to a coach from USC.

Every single day each coach keeps on yelling specific orders (i.e: signals) . The twin close to the UCLA coach ( the ectoderm side) can only hear the orders from UCLA because the coach is being so loud. On the other end, the other twin can only hear the information from USC (the notochord side) because that coach is being so loud.

Over time each twin will end up with a different “programming” and behave differently. One of them has become a UCLA Bruin, the other one has become a USC Trojan.

Back to Neuroanatomy

(Which is way more interesting than college competition!)

The neurons that will develop from the alar plate will become “sensory neurons,” whereas the neurons from the basal plate will become “motor neuron.”

[box]You can see this distinction when you look at a segment of the spinal cord. Neurons in the posterior horns tend to be sensory neurons, and neurons in the anterior horns tend to be motor neurons.[/box]

As the neural tube starts growing in lengths, different parts of the tube start differentiating as well.

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• The frontal part (rostral side) differentiates into something that we can now call the prosencephalon (or forebrain).

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• The prosencephalon will itself differentiate into the telencephalon and the diencephalon.

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• The middle part of the neural tube will become the mesencephalon (or midbrain). The mesencephalon will stay as the mesencephalon.
• The caudal part of the neural tube will differentiate into the rhombencephalon (or hindbrain).

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• The rhombencephalon will later on differentiate into the metencephalon and the myelencephalon.

All these words might look kinda complicated because they are long.

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Just remember that “cephalon” refers to “brain.” So every time you see “cephalon” at the end of a word, you know that it’s something about the brain.

Next, look at what’s in front of “cephalon.”

“Pro” usually means “first” and in this case “frontal.” (both first and frontal start with an “f” 🙂
“Meso” usually refers to the “middle.”

And now you’re left with “Rhomb,” which for our sakes, we’ll take as meaning the caudal part. (But “rhombus” actually refers to an “equilateral quadrilateral”…. )

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If you want more articles and videos about the Nervous System, you can find them here. More resources are available to help make Biology fun. I invite you to absorb all the content you can find here at Interactive-Biology.com.