1. Intro to Developmental Neurobiology

How does a simple two-cell organism--a zygote composed of sperm and egg--become a sophisticatedly complex organism? Specifically, how does the nervous system, which oversees all behaviors, senses, and cognition of these complex, sentient beings, develop?

You may be surprised to learn that early stages of neurobiological development is a highly conserved process (meaning, evolutionarily identical process) across numerous species, from frogs to mice to humans. This deep, evolutionary rootedness should intrigue and interest all of us and make us ponder--how do cells know the intricacies of inter- and intra-organism differentiation?

Before we delve into the chronological specificities of developmental neurobiology, let us first explore a few core neurobiological concepts (don't worry, no memorizations or tests here).

Concept 1: The Embryonic Life Cycle

Do NOT become overwhelmed by this illustration and the associated terms, especially if you have not encountered it before. Here's what you need to know: males and females of a species produce gametes (e.g., sperm and eggs, respectively). Note: the cells that develop into gametes are called germ cells, whereas all other cells in your body are called somatic cells (this biology language may be generally helpful to keep in mind).

We will start exploring this illustration clockwise, starting from the first "blob" above the frog.

Gametes are haploid cells, meaning each gamete only contains one copy of the parental DNA. When a sperm fertilizes an egg (See the illustration right above the frog), a diploid zygote is created, allowing for cell division (mitosis) to start. The cell first cleaves, or divides, into two  (See the illustration of the blob with two halves, above the illustration of the zygote). From this point, we refer to this cell mass as an embryo (2+ cells) instead of zygote (sperm + egg), and much later, fetus. The embryo composed of two cells then divides into four, and so on (See the third blob from the left). At a certain point of cell division, the embryo is composed of many, many cells, and enters its blastula stage (See 4th blob, referred to as a blastula), which we will discuss in the next lesson. Do NOT worry about the later stages and the animal/vegetal poles of the cell(s) just yet; I promise we will cover that in a later lecture. This is all you need to know from this illustration for now. Not too bad, eh?

Concept 2: All Cells in the Body are Genetically Equivalent

Literally all of them. All of these cells have the same genome (i.e., the same complete set of DNAs) because they are YOUR cells. So why on Earth do they look and function so differently? Because of gene regulation. When these cells differentiate during development, certain genes are suppressed and/or turned on in order for the cells to develop into a specific type of issue, or in other words, determine the cells' fate. However, these genes are not missing or discarded; your genome simply has its own way of silencing the phenotypic expression of certain genes, making the cells unique to their functionalities.

This is all you need to know for now as we begin studying neurodevelopment. I hope you learned something new (even if it is a trivial factoid) and are finding developmental neurobiology interesting (even if just a little bit; we can nurture that!). Hope to see you back.

Neurocookie.org believes that neuroscience should be fun, accessible, interesting, jargon-free, and welcoming to all who wishes to learn, no matter your background.