Hey there! I’m Alie Astrocyte, and you’re watching Neuro Transmissions!
We’re going to start talking about how the brain uses neurons
to send signals throughout your body.
You’ll find that it’s a lot like a giant, squishy battery.
And like a battery, this process is electric!
[Electric Slide playing]
Last week we found out that neurons are the information superhighway for sending signals
from cell to cell, transmitting information across your whole body.
But how does your brain actually do it?
To make it a little easier to visualize, let’s look at a battery for a second.
Keep in mind, this isn’t a perfect analogy, but it’s a good place to start!
As you can see, batteries have three main parts: a cathode, or positive end,
an anode, or negative end, and
an electrolyte, a solution between the two.
Chemical reactions within the battery cause electrons to build up at the negative end.
These electrons are unstable, and don’t like to be packed up with their fellow electrons.
Like wild horses or an ex-boyfriend, they need their space.
This means that they will try to move to a place with fewer electrons whenever possible.
When a wire connects the positive end of the battery to the negative end,
this lets the electrons run down the wire.
Usually, there’s something along that wire that uses those electrons for power.
Like a lightbulb lighting up.
The electrons are trying to reach an equilibrium,
where they’re as far apart from each other as possible.
Once the equilibrium has been reached, the battery is used up, and is “dead”.
It has no more electrons left to flow, and so, no more current.
Your brain uses a similar process, except it uses something your body is jam-packed with.
Ions.
If you’ve taken a chemistry course, you might remember that ions are charged atoms,
and can be positively or negatively charged depending on if it gains or loses electrons.
Need more information about atoms and ions? Check out some of these other YouTube videos!
In the nervous system, the main ions are sodium, potassium, and chloride.
Let’s take a closer look at how these ions send signals.
Here’s a neuron.
All cells have a membrane called the phospholipid bilayer, which is very good at insulating
the inside of the cell from the outside.
Built into this membrane are channels that allow ions to move easily across the membrane.
Imagine this neuron has a lot of positively charged ions inside of it, mostly potassium,
and some negatively charged ions, like chloride.
Since the inside of the neuron has a very high concentration of potassium compared to the outside
the potassium ions “diffuse down the concentration gradient”.
That is, they try to even out their concentration between the inside and the outside of the cell.
Just like the electrons trying to move down the wire on the battery.
This means that potassium ions flow out of the cell through the channels,
leaving behind their negatively charged friends.
These negative ions build up a negative charge inside of the neuron.
Eventually, this negative charge starts pulling on those outward-moving potassium ions.
We end up with a balance between the diffusion forces pulling potassium out
and the negative charge pulling potassium back into the cell.
This is called the equilibrium potential.
This creates a “potential difference”, or a voltage, just like a battery,
across the membrane.
But just like a battery without the wire,
the positive and negative ions build up along the membrane with nowhere to go.
When the cell isn’t sending a signal, this is called the “resting potential.”
Most neurons have a resting potential of about -70 millivolts.
Not a whole lot.
Especially when you consider that a AA battery has a voltage of about 1.5 volts, or 1,500 millivolts!
Resting potential can be a very complex idea to explain.
But just so you know, even this is a very simplified version of the resting potential.
It’s really much more complicated, mostly because the concentrations of other ions,
like sodium and calcium, have an effect on the electrical potential.
There are all sorts of calculations used to measure it, such as this equation,
called the Nernst equation.
We won’t cover it in a short video like this.
But if you would like to learn more, check out the description for more information.
For now, let’s focus on some things you should remember:
potassium is much more highly concentrated inside the cell,
and sodium and calcium are much more highly concentrated outside the cell.
This will be important going forward.
So, now we’ve got this neuron with a negative charge inside the cell,
and a positive charge outside of the cell.
How does this transmit a signal? Where’s the action??
Patience!
Like I said, this is a pretty complex concept.
Come back next week and I’ll tell you all about the action.
The action potential, that is!
I’m Alie Astrocyte, and until our next transmission, over and out!