MadSci Network: Cell Biology Query:

I had a hard time finding a clear answer on this question, so I think we should do the math ourselves. Here are the facts: Most estimates say we have about 100 billion brain cells (neurons), and about ten times that many, or one trillion, support cells (glia) that help the neurons. We'll just concentrate on the neurons themselves. The brain weighs about 3 pounds, and after age 20, you lose about a gram of brain mass per year. Three pounds is about 1.4 kilograms (scientists work in the metric system, so that's the units we'll use here). So�if the brain weighs 1.4 kilos (1400 grams) and there are about 100 billion neurons, that comes to about 70,000,000 (70 million) neurons per gram. Now we could stop here and say that we lose 70 million neurons a year, or about 190,000 per day, but that wouldn't really be right. That's because most of that gram isn't really neurons dying. Some of that loss is glia (support cells) dying, some of it is because the neurons are shrinking but not dying, and some of it is that the neurons lose some of their insulation (myelin), which makes them slower, but doesn't cause them to die. Even if we say that only 5% of the gram is neurons actually dying, we get neuron loss of about 9,000 neurons a day! That seems like a lot, doesn't it? But when you think about it, that's nothing compared to the number you have left. A side note: This is all assuming you're a person who takes care of yourself. But there are lots of things people do that cause much higher rates of brain cell death. The big one is using certain drugs. Not all drugs cause brain cells to die, but the ones that do are very damaging. Ketamine, nitrous oxide (laughing gas) and volatile inhalants (glue, gasoline, paint thinner) can cause brain cell death at THIRTY TIMES normal rates - that's almost 300,000 neurons a day! And alcohol also increases the rate of brain cell death, but less than the others. Please contact me with any questions! Brenda

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