Dear Dr. Universe,
In our class we have studied different cells in the body. We would like to know why can’t a person grow new brain cells?
La Center Middle School
La Center, Washington
I went to talk to Professor Dipak Sarkar here at Washington State University. He studies the nervous system, and he gave me a surprise. He told me that humans CAN grow some new brain cells.
But there are actually two kinds of brain cells, the neurons and the glial cells. Neurons are cells that carry information. The glial cells help support the neurons. Scientists think they also have something to do with storing your memory. So even as you read this, glial cells are continually multiplying.
As for neurons, scientists are finding that some neurons DO have the potential for division, which is how new cells come to be. For example, the olfactory neurons, which carry smell signals from your nose to the brain, are replaced throughout your whole life.
However, you are right that most neurons do not divide.
Well, it becomes kind of a philosophical question, like “Why am I?” But I know you want a better answer than that.
As you probably already know, the eventual you started out as a “zygote.” A zygote is the fertilized egg from your mom. From there, the cells start dividing and differentiating. That means they start becoming what they’re meant to be, like muscle cells and eye cells and nerve cells. Almost all of your neurons—your entire nervous system, in fact—was formed when you were inside your mom.
And here’s the really amazing part: In order to produce the eventual one trillion cells that your brain eventually has, you had to develop an average of 2.5 million neurons every minute you were a fetus inside your mom! (Just to give you an idea of how many neurons you have, let’s say you started counting right now, without any breaks or sleep or anything. Counting to one trillion would take you over 32,000 years!)
But once a neuron becomes a neuron, that’s what it is until you die. Actually, that’s not that unusual. For instance, most muscle cells do not divide. But they do grow in size. If you do a lot of exercise and get bigger muscles, you don’t get any more muscle cells. You just get bigger ones.
Same with the brain. That doesn’t mean that your brain is done growing, though! Think about it. When you were born, your brain weighed about 12 ounces. Or about 350 grams. (We’ll switch to metric, because that’s how scientists measure things.) When you were one year old, it weighed about 1,000 grams. Right now, it weighs probably about 1,300 grams. When you’re an adult, it will weigh about 1,500 grams (a little more than three pounds).
So, if you’re born with all your neurons, how come the brain gets heavier?
Well, the neurons themselves grow in size, like muscle cells. Also, you grow more glial cells, as you need more memory. (Just think how many more glial cells you’ll have once you’re done reading this.)
But once you’re about 20 years old, you start to lose neurons. In fact, you start losing about 50,000 neurons every day! By the time you’re 75, you will have lost about 10 percent of your neurons.
But this doesn’t mean that you’re only 90 percent as smart as when you were born. That’s because even though you’ve lost some neurons, the ones that are left can form new branches of fibers and new connections, or synapses, between them. These make up for the ones you’ve lost.
Finally, here’s something to think about. There are lots of things that help fine-tune those synapses and the actual development of the neurons. These things include what you eat, what you experience–and (get this) learning.
So what this means is you either use it or lose it.