okay so here we're going to look at brain development now embryologically all central nervous system structures come from something called the neural tube which is essentially a tube of cells made of embryological stem cells with a fluid filed center now this neural tube as it grows in elongates turns into three primary vesicles or sort of bulges of this tube we have the proen sephylon mezen sephylon and renon which become the forbrain midbrain and hindbrain respectively think of the forbrain as like the very tip of the tube midbrain is just being a little bit you know uh deeper along the end of that tube as well as the hindbrain and then the rest of the tube itself becomes the spinal cord so if you look at here under a this is what the neural tube looks like early on in development so shown in kind of a a dark gold here we would find that these are actually the embryological stem cells that would become neurons and glea later and there's a fluid filed Center of this tube as well now as this neural tube begins to grow and differentiate we get the proen sephylon the mezen sephylon and the ren sephylon which are the three primary vesicles here or sort of bulges of the neural tube now as this neural tube begins it to develop we get secondary brain vesicles so our proen seylon becomes the telen seyon and dlon the mesen seylon stays as the mezan seylon and then the ramen seyon becomes the metan and myin seyon as well as as well as the cerebellum now the rest of the neural tube uh just becomes the spin cord and now these structures here will begin to differentiate further in development and into adult brain structures where the telen sephylon makes things like your Cal hemispheres your dlon stays as the dlon which includes your Thalamus hypothalamus and epithalamus as well as your retina of your eye the mesen seylon is the midbrain and then our medon becomes the pwns and cerebellum where a Mylon becomes the medulla ablang now what's interesting then is that these brain regions are also named for the fluid-filled spaces that they surround so in an adult brain we'd find that the telen sephon here which makes your cerebral hemispheres uh surrounds these fluid chambers called lateral ventricles our dlon surrounds the third ventricle our midbrain surrounds the Cal Aqueduct our ponds and cerebellum as well as our medulla ablang are near the fourth ventricle and we find a fluid filed space in the spanic cord called the central Canal so looking at the neural tube in more of a three-dimensional type of view we would see that the the tube begins to kind of fold and uh differentiate and start to form these vesicles that are these bulges of the tube itself so you find the tonyon diyon med mezan Medan and myin sephylon um now those actually form what we call the brain stem dlon you find deeper within the brain and our telen sephylon is the majority of the volume of our brain because it forms our cerebral hemispheres now if you start to look here as the neural tube differentiates and grows we see the tel enlon starts to get so large that it surrounds and encases the diyon whereas our brain stem stays separate now adult brains have four major regions we have the hemispheres cerebral hemispheres dlon our brain stem and our cerebel so if you look at an adult brain here you can see that it's even further differentiated where the telen sephylon forms the cerebral hemispheres here that becomes so uh overgrown that the brain matter has to form these infoldings which is why it looks sort of uh pruned here on the surface uh it actually completely surrounds the diyon which is now deep within the tonon itself and then our brain stem here is made of our midbrain ponds and medulla ablang and back here the hindbrain is the cerebellum now uh inferior to that we have the rest of the neural tube which is the spinal cord at this point so if you took a cross-section of the central nervous system you'd find that there's gray matter and white matter within it gray matter is darker regions of the tissue and white matter are lighter and the reason why white matter is lighter than gray matter is that it's primarily made of melinated axons that are mostly made of lipids and lipids are kind of whitish which gives white matter its lighter appearance gray matter is mostly made of non-myelinated neurons and cell bodies but because these cell bodies contain a lot of organal and protein it gives them more of a grayish appearance to them now if you look at a cross-section of the spinal cord here we'd find that you you see gray matter deeper and it surrounds a central Canal which is the vestage of your neural tube as well as some white matter around that now uh if you took a cross-section of the brain stem we again we would see lots of gray matter here in fact gray matter that's located deep within the brain we actually call nuclei so these would all be examples of collections of gray matter called nuclei and if you look at a cross-section of the telen sephylon or C cortex we'd find that um you know out here we have the cortex which is gray matter on the outer surface of the brain here and then we also find gray matter deeper within the brain forming more nuclei like in within the diyon and all of this in between is white matter that's involved with communication of information now the ventricles are large fluid filled chambers that are continuous with one another so if you go back here and you look at a a cross-section of the brain you see that there are it's not completely solid there actually are spaces within the brain and these would normally be fluid filled with cerebral spinal fluid so what happens here is that in the cerebral hemispheres we have our lateral ventricles which are located deep within each hemisphere and they're kind of these large c-shaped structures now each ventricle is also connected to the third ventricle so the lateral ventricles are interconnected by the third ventricle through this interventricular frame and of Monroe and then the the third ventricle is connected to the fourth by something called the Cal Aqueduct so if you looked at a picture here of your ventricular system we'd see our large lateral ventricles found within each cerebral hemisphere those are connected to the third ventricle by the interventricular fan of menr and then your third ventricle is connected to the fourth by the cerebral Aqueduct here now if you look coming off the third the fourth ventricle here we see our Central Canal which can continue down the spinal cord and there's even actually openings on the side which are called the apertures that allow for cereal spinal fluid to exit and surround the outer surface of the brain to provide some additional protective cushioning so if you look at a side view here of your ventricular system again you'd see the lateral ventricles third ventricle the fourth ventricle and what connects the third to the fourth ventricles the cereal Aqueduct coming off the fourth ventricle we have our Central Canal as well as our aperture that allows for CSF to drain outside of the brain and then what connects the lateral ventricle to the third is the interventricular forment of Monroe now what keeps these lateral ventricles separated and um they don't actually don't communicate with flu with each other directly is something called septum paldum and septum pum is a very thin sheet of tissue that separates the two lateral ventricles within each hemisphere