In a 2013 Science paper, researchers reported that when mice were asleep, their interstitial spaces expanded by 60%, and the brain's glymphatic system cleared beta-amyloid (the protein that makes up Alzheimer's disease's hallmark plaques) faster than when the rodents were awake. Studies suggest this waste clearance process mostly happens during sleep. In what's called the glymphatic system, waste products from the interstitial fluid surrounding brain cells move into the CSF and away from the brain, according to the Society for Neuroscience.
In addition to cushioning the central nervous system, CSF clears waste from the brain. This fluid circulates around the brain and spinal cord, cushioning it from injury, and is eventually absorbed into the bloodstream. The brain also has four interconnected cavities, called ventricles, which produce what's called cerebrospinal fluid (CSF). It plays a role in coordination and balance and may also have some cognitive functions. The cerebellum lies beneath the cerebrum and has important functions in motor control. The hypothalamus connects the nervous system to the endocrine system - where hormones are produced - via the pituitary gland. Except for olfaction (sense of smell), every sensory system sends information through the thalamus to the cortex, according to the online textbook, " Neuroanatomy, Thalamus" (StatPublishing, 2020). The thalamus relays sensory and motor signals to the cortex. (Image credit: Mark Garlick/Getty Images)īetween the cerebrum and brainstem lie the thalamus and hypothalamus.
This gives axons (thin strands through which electrical impulses are transmitted between neurons) a white appearance, and so these axons are called the brain's "white matter." The brain also has about the same number of non-neuronal cells, such as the oligodendrocytes that insulate neuronal axons with a myelin sheath. The human brain contains about 86 billion nerve cells (neurons) - called " gray matter," according to a 2012 study published in the Proceedings of the National Academy of Sciences. The cerebrum, which is the main part of the brain located in the front area of the skull, makes up 85% of the brain's weight. The average male has a brain volume of nearly 78 cubic inches (1,274 cubic centimeters), while the average female brain has a volume of 69 cubic inches (1,131 cubic cm).
On average, male brains are about 10% larger than female brains, according to Northwestern Medicine in Illinois. (1.4 kilograms) and makes up about 2% of a human's body weight.
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