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Let’s start by looking at the physiology of the nervous system, which is divided into the central and peripheral nervous system. The central nervous system includes the brain and spinal cord, while the peripheral nervous system includes all the nerves that connect the central nervous system to the muscles and organs. The brain is divided into the cerebrum, which consists of the two cerebral hemispheres, the cerebellum, which sits down at the base of the skull, and the brainstem, which is located right in front of the cerebellum.
Now, the brain is protected from the rest of the body by three meningeal layers. From outside to inside, these are the dura mater, arachnoid mater, and pia mater. Between the arachnoid and pia mater there’s the subarachnoid space, which houses the cerebrospinal fluid. The cerebrospinal fluid is a clear, watery liquid that cushions the brain from impact and bathes it in nutrients.
Zooming in, the cells that make up our brain are called neurons and they receive and send electrical impulses to one another. Now, neurons need a lot of oxygen and nutrients to function properly, so the brain has a rich blood supply. But for any nutrients to enter and leave the brain, they have to go through the tightly regulated blood-brain barrier. This refers to the endothelial cells in the blood vessels of the brain which are so tightly bound to one another that they only allow certain molecules to slip through them.
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