Your brain is not just neurons.
Turns out there are other cells doing
important work up there, too!
Neurons get a lot of attention for being the cells that do
all of the communicating in our brains and bodies.
But about half of your brain is made up of
non-neuronal cells called glia.
And these cells have their own important roles.
Hey there!
I’m Alie Astrocyte.
And this week, we’re highlighting another one of
the brain’s glorious glial cells: microglia.
Thanks to evolution, we have this handy thing
called the blood brain barrier, or BBB.
We’ll probably talk about this more in a later video,
but to put it briefly, the BBB is basically a set of properties
that are unique to the blood vessels in the brain.
These specialized blood vessels make it
very, very difficult for infectious agents,
like bacteria, to get into the brain and spinal cord.
But, the trade off to that is that other, beneficial things
like immune cells, can’t get into the brain either.
Microglia are the brain’s answer to that problem.
Basically, these cells take care of the stuff that
other immune cells do in the rest of the body.
But in the brain instead.
These cells make up around 10 to 15% of all brain cells,
and they can move around a lot, doing
tons of different jobs depending on what state they’re in.
Resting microglia have a small cell body
that stays in one place, while long, thin cellular branches
project out and move around, monitoring the surrounding area.
Kind of like the arms in The Matrix.
...Except not harvesting humans.
These act sort of like a security system
They’re tracking the local environment,
keeping an eye out for any kind of danger.
They can also clean up any dead cells and
cellular debris they come upon, moving to
suck up and break down the junk they find.
When something activates the microglia,
like a brain injury or infection,
they go to work to fix the problem.
These active microglia change their shape,
pulling in their branches and becoming more “bushy”.
And start multiplying to increase the number of microglia in the brain.
They also release proteins called cytokines
that make it easier for other immune cells, like T cells,
to get into the brain to help deal with infections,.
Some microglia become like a clean up crew.
They travel through brain tissue to the site of the injury
where they engulf any foreign materials or debris
and releasing chemical signals to promote inflammation in the tissue
in an attempt to kill off any invading bacteria.
This isn’t always a good thing.
Some of those signals can actually promote cell death.
So in some ways, microglia can actually
make things worse during infections or after injury.
But after things settle down, microglia release signals
that recruit neurons and astrocytes to the area to help the tissue heal.
Keeping the brain healthy and protecting it from invasion is pretty important.
And just like astrocytes, it turns out that microglia have
a few tricks up their sleeves.
Some fairly recent research has found that
microglia aren’t just important for cleaning up debris after injury.
They actually play an active role in cleaning up extra synapses.
During development, your brain actually grows more neurons
and forms more synapses than it needs.
The connections that are used get strengthened and solidified,
but the ones that aren’t end up being broken down.
Microglia can come in and “prune”, or pinch off, extra synapses.
Then they gobble up the debris from the extra neurons as they die off.
It’s also thought that microglia could be playing a part in
neurodegenerative diseases like Alzheimer’s disease.
Microglia in Alzheimer’s disease become activated,
and then release toxic chemical signals that lead to
neuronal death and degeneration.
So these cells aren’t just part of the immune system.
They’re a really important part of keep the brain clean and organized
so that your neurons can continue communicating clearly with one another.
Pretty cool, right?
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Until next time, I’m Alie Astrocyte.
Over and out!