Welcome to basics week at Neurotic Physiology! This post covers part two of brain neuroanatomy, using Sci's OWN BRAIN as reference. Yes, I am awesome. I know.
Ok, so I thought I would be able to do this brain stuff in TWO entries, but I think it might have to be three. After all, the brain is a wondrous, glorious world of awesome, and MY brain in particular is especially nice. Last time I talked about the outer features of the brain and the division of the brain into traditional lobes of form and function. So today I'm going to give a brief intro to things with arcane sounding names, like dura mater and the choroid plexus, and talk about why it's ok that your brain is full of holes.
So let's begin!
What I want you to focus your attention on here are the outer edges of my brain. Right here:
What I've shakily outlined for you in the photo above are two of the three kinds of coverings that surround your brain. We'll get to the third covering once I've covered the first two. Why three coverings, you say? Because, contrary to a certain amount of popular belief, your brain isn't actually rattling around in your skull. Instead, it is surrounded by three layers of...stuff...one of which is filled with fluid, leaving the brain floating comfortably surrounded like a baby in a womb.
The outer of these layers is the one that I've lined in yellow. We call this the "dura mater", which literally means "hard mother". And it is a HARD motherf**ker. Seriously, you can't rip this stuff. We have some accompanying our neuroanatomy brains. I don't want to know how old it is, but it still looks just as good as the day it was pulled out. In interesting medical terms, a subdural hematoma is when you tear veins in your head, and blood builds up in your dura. Very nasty.
The middle of the three layers is scribbled in in red. This is the arachnoid mater, which means "cob-web like". It's a thicker layer, as you can tell, and very soft, filled with cerebrospinal fluid. Cerebrospinal fluid is one of the little known heroes of your brain. It surrounds and fills every crevice, and produced in volumes of almost half a liter a day! This is the cushion your brain relies on most to get it through the bumps and bruises of life. I might add that it is also pretty easy to make up in the lab.
So where do we get these vast quantities of cerebrospinal fluid? From here:
that clumsy outline you see in green outlines my very nice, clear choroid plexus. The choroid plexus is a dense network of capillaries that are constantly making cerebrospinal fluid. When you take them out of the brain, they look like little fluffy fan sponges.
So under the arachnoid layer, there is one further layer. Unfortunately, it's going to take some advanced in technology before we see one of those on a brain scan. The pia mater (meaning "tender mother") is a thin, delicate layer, so close to your brain that it thinly veils each sulcus and gyrus. Getting one of these off your brain in order to dissect is ANNOYING.
Ok, so you might have noticed that the choroid plexus on either side appears to be in holes in my brain. My brain is full of holes. Believe me, this is not an uncommon occurance. Everyone's brain is full of holes, though some of course have more than others. There are four main ventrcles, with various channels running between them. These ventricles are what circulates your cerebrospinal fluid. Two two you can see here:
Are the paired lateral ventricles, while the third and fourth ventricles are more easily seen on the midline, here:
The first and second ventricles vanished and were squished away during development. Each ventricle contains a separate choroid plexus to supply the brain with cerebrospinal fluid, though you can only see the ones in the lateral ventricles in my scan.
And with that, folks, Sci is going to call it a night. Tune in next time (which may be next week) for the final installment of the awesomeness that is Sci's brain!!