Neurons need to send a lot of signals, pretty far and pretty fast.
And as we talked about in our very first Neuro Transmissions video, myelin helps with that
by acting like insulation around the axon, letting neurons send signals quickly.
But where does that myelin come from?
Well, once again, you can thank your glial cells for that!
Hey there!
I’m Alie Astrocyte, and in this episode of Neuro Transmissions, we’re talking about
another kind of glial cell - this time, it’s the oligodendrocyte.
[Intro]
“Oligodendrocyte”. The word is long and silly, but we’d be pretty useless without them.
Oligodendrocytes are among the last cells to form in your brain.
They produce proteins that are important for strong, healthy neurons, like brain derived
neurotrophic factor - BDNF - and insulin-like growth factor 1 - IGF-1.
These proteins help new neurons grow and form synapses, as well as supporting existing neurons
and keeping them healthy.
Oligodendrocytes also have very special lipid membranes, and they use them to form the
myelin sheath around neurons.
This process is called myelination.
Myelination isn’t a fast process- at birth, there are very few brain regions with much
myelination, and the process continues until you’re in your twenties!
Myelin was named by the German pathologist Rudolf Virchow, from the Greek word “myelós”,
meaning marrow, because when he first saw it, he thought it was actually inside the
neurons.
Since its discovery, we’ve discovered that myelin is actually wrapped /around/ the neurons
- and this makes it really useful.
Why?
Well, as we’ve discussed, neurons use electrical signals to communicate with each other.
And for us to function normally, in real time, those signals have to be sent across some
pretty long distances - like from the base of your spine to the tip of your toe - and
it has to be done quickly.
But physics puts some limitations on how quickly neurons can send their signals - the velocity
of the signal depends on the diameter of the axon.
The thicker the axon, the faster the signal - but we have wayyy too many brain cells for
our axons to be really thick.
Our heads would be huge!
So vertebrates evolved myelin to get around the problem.
It keeps the ions close to the cell membrane so they can’t escape, preserving the strength
of the signal as it travels down the line.
And there are gaps in the myelin sheath, called Nodes of Ranvier, where ion channels are clustered
so the signal can be maintained and amplified.
This set up basically lets the electrical signal “jump” from node to node, so the
message can move /very/ quickly - and this is called saltatory conduction.
So myelin - and therefore oligodendrocytes - are a really important part of what makes
our human brains so special.
Oligodendrocytes are actually a part of the central nervous system.
This means that they’re only found in the brain and spinal cord.
Myelination in the peripheral nervous system - the rest of the nerves in your body - is
taken care of by Schwann cells.
And because myelin is so crucial for normal signaling in the brain and body, when something
causes the myelin to break down, things can get pretty bad.
Loss of myelin is part of the reason that things like strokes and spinal cord injuries
can be so difficult to recover from.
It’s also a huge part of the disease multiple sclerosis, or MS.
Researchers are trying to understand what causes MS, and the best theory we have so
far is that it’s actually an autoimmune disorder.
Basically, our immune cells get confused and instead of just attacking intruders, they
start attacking the myelin sheath.
Once the sheath gets damaged, the nerves are left exposed, and the brain can’t signal
properly to the muscles.
This leads to all kinds of dysfunction, like weakness, numbness, and even paralysis.
Scientists think that if we can figure out ways to protect or regenerate the myelin sheath,
we can help stop and even reverse the symptoms of MS, which could be a huge help for people
struggling with the disease in the future.
Because they’re still relatively understudied, it could turn out that oligodendrocytes and
the myelin sheath play important roles in other disorders, too - so don’t underestimate
these unassuming glia!
Thanks for watching this episode of Neuro Transmissions.
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Until next time, I’m Alie Astrocyte - over and out!