CSF buoyancy reduces the brain’s apparent weight. Approximately what does the brain’s weight decrease from and to when supported by CSF?

CSF buoyancy reduces the brain’s apparent weight. Approximately what does the brain’s weight decrease from and to when supported by CSF?

• A. 1500 g to 50 g
• B. 1000 g to 100 g
• C. 2000 g to 100 g
• D. 500 g to 25 g

Answer: (A)

The brain effectively “floats” in cerebrospinal fluid, so CSF buoyancy greatly lowers its apparent weight. The brain’s actual mass is about 1.4–1.5 kilograms, but the upward buoyant force from the displaced CSF reduces the net downward weight to roughly 50 g. So the apparent weight decreases from about 1,500 g to around 50 g. That matches the option describing a drop from ~1,500 g to ~50 g. The other options don’t fit the typical brain mass and the resulting very small apparent weight.

The brain effectively “floats” in cerebrospinal fluid, so CSF buoyancy greatly lowers its apparent weight. The brain’s actual mass is about 1.4–1.5 kilograms, but the upward buoyant force from the displaced CSF reduces the net downward weight to roughly 50 g. So the apparent weight decreases from about 1,500 g to around 50 g. That matches the option describing a drop from ~1,500 g to ~50 g. The other options don’t fit the typical brain mass and the resulting very small apparent weight.