1. The blood brain barrier is a protective network of blood vessels and tissues that regulates the movement of substances between the blood and the brain. Compared to similar membranes in the rest of the body, the blood brain barrier is composed of cells that are particularly close together. The gaps between cells that are normally present throughout the body and that allow larger molecules to pass through it are plugged up by special cells called astrocytes; this effectively create tight junctions that only small, fat-soluble molecules (and some gasses) to move through freely.
While the vast majority of the brain is protected by the blood brain barrier, there are deliberate weak points in the barrier that are designed to allow substances to cross more freely. These areas are less restrictive because they are near circumventricular organs, parts of the brain that monitor the makeup of the circulating blood. Why might that be important? If you eat something that makes you really sick, the body responds by vomiting in order to protect itself. How could the brain initiate this response if it was unable to recognize the toxic substance? It couldn’t!
Other weak areas of the blood brain barrier are also nearby circumventricular organs (those that monitor levels of hormones in the blood, regulate bodily fluids, etc.) in order to make important adjustments in response to bodily functions. These weak points are not accidental, but rather a deliberate and essential component of the bidirectional (2-way) communication that exists between the brain and the rest of the body!
2. The human brain is divided into 2 halves (referred to as “hemispheres”). The right and left hemispheres of the brain are largely symmetrical, though they do vary in terms of the regions of the body they control and the specific functions that they perform best. The hemispheres process sensations and control movement on the opposite sides of the body (known as “contralateral” functions) and process information from the opposite visual field (what you see with your left eye is processed in your right visual cortex and vice versa).
If one hemisphere is dominant, it is likely to be the opposite of the hand that you most naturally write with (the left brain for the majority of people). The popular notion of “right brain” and “left brain” people is a generalization and simplification of reality; however, there is research evidence that demonstrates important functional differences between the two sides of the brain (referred to as “lateralization”). While the right side of the brain has more visual and auditory processing abilities, including spatial skills and artistic ability, the left side contains regions that are highly involved in the ability to speak and comprehend language and other forms of data (including those needed for calculations, analysis, and orientation to space and time).
Even though there are specialized functions on both sides of the brain, the lobes rarely (if ever) work alone. You may consider yourself more of a “right brain” or “left brain” person, but it’s the complex interactions between the lobes that really underlies your ability to function in the world.