Inside your head you have about 86 billion
brain cells, or neurons. That’s Joe, from It’s Okay To Be Smart. Now all those neurons live in particular regions
of your brain. Take these here, those are the ones that help you see, whereas, well,
way over here, those are the ones that help you move. And it’s pretty amazing to think that these
neurons connect with other neurons in all of these areas to form this crazy network
that controls all of your thoughts, feelings and actions. It makes me wonder — where do all these neurons
come from? It is determined when your brain starts growing which neurons will be responsible
for you getting excited about history or math or labradoodles? Is it weird that I wonder
these things? It’s okay to be smart. Well your brain starts growing when your whole
body is smaller than a dime. The speed of growth is incredible. During early pregnancy,
neurons develop at the rate of 250,000 every minute. Of the 40 weeks it takes a baby to grow, your
neurons are mainly developed between 10 and 20 weeks and then these newly formed neurons
start to migrate. This part is really cool. They head off to regions of the brain where
they’re gonna live the rest of your life. Now each neuron carries a special code that
tells it exactly where it’s going to end up. And as they migrate, they start off as just
cell bodies, the control centres and factories of the neuron. And It’s not always fun travelling by yourself.
With your neurons migrating, glial cells glue neurons together to give your brain structure. Once the cells reach their final destinations,
then connections among them begin to develop. Synapses form, the tiny space between neurons
that let them communicate with each other. And a fetus lets you know when this is happening.
They start to have periods of activity and rest — they can nap! And even yawn. During the last 8 weeks of a pregnancy, a
fetus can hear, smell, respond to touch and light. And they can learn.
In one study women read The Cat in the Hat out loud for the last 6 weeks of their pregnancy.
And when their babies were born, they were able to suck on special pacifiers that allowed
them to hear their Mother reading that story to them. And they quickly adapted to do it
in just the right way to hear their Mother’s voice. Babies brains are incredibly adaptable. They
form 700 new connections between neurons every second in the first years of life and by the
time they’re 3, their brains have formed 1000 trillion connections. By age six, your brain is 90% of your adult
brain size. While it doesn’t grow a lot more in size, your brain development extends through
late adolescence, and arguably throughout the rest of your life. While you’ll develop new connections for the
rest of your life, most of your brain has been there before you were even born. So why are our brains in our heads to begin
with? Head over to It’s Okay To Be Smart, where Joe tackles evolution head on. And if
you haven’t already, subscribe to BrainCraft! I have a new episode out every other week.