Development

Okay, so I know most of the people visiting this blog find biology awfully boring.
Well I can't seem to complain given that I hated it too during school. Anyway lets put all that behind and try to make things interesting.

Now Twish had some really interesting posts which definitely might have made all of you think about the brain in terms of circuits, processing, perception and a whole lot of other things. However before I put up a post about the workings of the brain, I have to first get everyone to know how the brain or for that matter any organ develops. (wait, it doesn't start getting boring here, I am gonna talk about circuits in a totally different way).

So lets start with two cells i.e the resultant of the fusion of the sperm and the ovum. So what happens next. How is it determined which cells become what in the course of division of these two cells to form the millions of cells that is us? How is it that the neurons are formed only in the brain and the spinal cord and other regions? What makes the heart not be in the place of the kidneys and the blood cells to be as they are? (No, this is something that isn't easily ascribed to the creations of a higher power namely God)

So what happens is a completely different branch of biology that is called Developmental Biology.
I can't promise you that I shall give you the answers to what makes the heart cells to not become neurons and vice versa but what I can say is that probably some of you might see the analogy between genetics and circuits.

So now lets get to the start of development. You have 2 cells and they divide something like 9 times over. Till this point none of the cells are in anyway different from one another (or atleast no one has been able to prove that they are). So these cells are called embryonic stem cells (ESC). Now once this stage has been reached what happens is that the embryo starts getting polarised, by polarised I mean to say that now you have distinct regions within the embryo which you can differentiate. Hence we now have an anterior (mouth) end and a posterior (anus) end. Similarly we have left and right sides and up and down distinctions.

But in turn how do two cells differ simply becuase of positions. This is due to a clever trick brought about by diffusion of protein products that have been passed on with the ovum(the sperm is a poor guy who contributes only DNA and no proteins).

So how do these circuits work?
Due to the proteins passed into the embryo by the ovum, these protein create a gradient by simple diffusion and the varying levels of these proteins at different areas "switch on" or "switch off" certain specific genes and these genes form certain other proteins and so on and so forth. Now the products of these genes are important for the activity of other genes and so forth. Thus what you have is a series of AND/IF/OR gates which function together in a highly complexical manner leading to different cells showing different reactions to the same stimulus.

Thus in most simple words, this is the basis of differentiation of cells to form neurons and muscle cells and liver cells.



I think this much is enough at one go, shall write more once I feel it has been adequately understood.