Sunday, January 22, 2017

Stuff I Learned - 2nd semester, Week #1

The brain has a large appetite for
glucose and oxygen.
This semester I'm taking a course called Systems Neuroscience. As the name implies, this course explores the various systems of the nervous system, and how they all work together. Last week marked the beginning of the course, and we began by exploring the blood supply to the brain. It probably goes without saying that adequate blood flow to the brain is important, as it is for all of the body's tissues. As it turns out, the brain has its own unique set of circulatory demands, and an uninterrupted flow of blood to the brain is even more essential than it is for many of the body's other tissues.

The brain has a disproportionately hearty appetite for food (glucose) and oxygen. Unlike other tissues in the body, though, the brain does not store reserves of glucose. Because of this absence of stored energy, the brain's health is entirely dependent upon the uninterrupted flow of fresh blood. Since the flow of fresh blood is so important for the health of the vitally-important brain, the circulatory system has back-up plans in case something goes awry with the primary circulatory pathways.

Four primary arteries bring fresh blood to the brain.

In the adjacent diagram, you can see the blood flow to the brain. The central ring is known as the Circle of Willis (CoW), and this brilliant design allows blood to flow to most regions of the brain, even if some of the brain's blood supply is deficient.

There are four primary arteries that supply the brain with blood; the two vertebral arteries, and the two interior carotid arteries. These four arteries, in turn, connect to the CoW, as seen in the adjacent diagram. If one of the supplying arteries were to be damaged, there would certainly be a reduction of blood flow to regions of the brain, though there would likely still be sufficient blood flow that the organism would survive. Like many roads lead up to a traffic roundabout, multiple arteries lead to the Circle of Willis. Embedded deeply within the brain, the CoW helps distribute blood flow throughout the brain's tissues, even in the event of an interruption in normal circulation.

An interruption to blood flow to the brain can bring about catastrophic results (stroke, for example), though the redundancy offered by the CoW makes it less likely that interruptions to brain blood flow are fatal.

Later this semester I'll be learning how the brain adapts to damage, and I specifically plan to write more about strokes. While the brain is very sensitive to interrupted blood flow, it also has a remarkable capacity to rebuild and revise its circuitry.

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