guru_urug,
There is no gap, per se. There is the inner table of the skull, then the covering of the brain (The meninges consist of three layers: the dura mater, the arachnoid mater, and the pia mater. The primary function of the meninges and of the cerebrospinal fluid is to protect the central nervous system.), then you have the brain itself. As you can see (you might want to look at this web site:
http://en.wikipedia.org/wiki/Meninges ) the brain is held pretty tightly inside the brain case.
That is so it doesn't get hurt when you throw your head around or get hit in the head. A really hard hit to the head (car accident), can cause the brain to ... (you have to sort of think about this in slow motion to get the idea) slide forward and crash into the front of the skull, then rebound and hit the back of the skull real hard. This is called a contrecoup injury. The brain really doesn't move more than a couple of millimeters, but you get the idea.
The meninges hold the brain in the skull and contain the cerebrospinal fluid (CSF). It helps to nourish and protect the brain and spinal cord.
So, like I told you about the Mayans, whatever the shape of the skull, the brain underneath it just forms to match it. It's just the way you are, and remember, that no two people are exactly alike. Everyone has little imperfections, that make that person unique.
Get control of your stress and your speech problems will probably away. And life will be a lot more enjoyable.
Good luck. Have fun in life.