Nervous System Foundations 04 How Nerve Cells Communicate

In this video,

We're going to go a little bit deeper into the weeds of how nerve cells function and how they communicate with other nerve cells in the body.

So to begin with,

A little bit of anatomy for you.

This is some basic nerve cell anatomy.

So nerves are really,

Really,

Really long and in the body they can be,

You know,

Even several feet long.

So this is a very compact version of it and it's definitely not to scale.

But anyway,

Here we are.

Over on this side,

You can see a great big blob with some fingers sticking off of it here.

The great big blob in the middle,

This whole part here,

Is what we would call the cell body.

That's kind of the meaty structure of the nerve cell.

In the middle,

The blue dot you see here is the nucleus and this is where the DNA and RNA are stored in the cell body.

Off the wings of the cell body here,

You can see these finger-like structures called a dendrite.

A dendrite is either in a terminal nerve cell where we would have a receptor,

So a nerve ending that's going to be detecting certain stimuli or in a cell that is receiving information from another nerve cell.

It's where the receptors lie for neurotransmitters and we'll get into that in a second.

But the dendrite is essentially the receiving end of a nerve cell.

Moving along here,

You're going to see down the center we've got what looks like a beaded string in the middle.

In the middle is the length of the nerve cell.

However,

Around it,

We have something called a Schwann cell.

A Schwann cell is a single cell that wraps itself around a nerve cell and then when they all join together,

They create something called the myelin sheath.

The myelin sheath is just a network of these cells that insulate a nerve cell and help it to be nourished and also help it to communicate faster.

Some cells are myelinated,

Some are.

It depends on the location in the body and the purpose of the nerve.

However,

For the purposes of this,

Just understanding that this is what it would look like if a cell is myelinated.

As you can see at the bottom here,

I have action potential written across the bottom with an arrow heading towards the axon.

We'll talk a little bit about what an action potential is in a second and its importance to communication,

But just understanding that essentially the action potential,

Which is the message that's being communicated along the nerve,

Travels from dendrite through the cell body,

Through the length of the nerve,

All the way over to the axon,

Which is the other end of the nerve that is what delivers the message onward.

If we were to think about the nerve cell as having a receiving end and then a delivering end,

The dendrite is what's receiving information and then the axon is what's passing along that information to wherever its final destination is.

Dendrites have,

Like I said,

If they are at the end of the nerve and they're at what we would call the terminal end,

They have something called a receptor.

A receptor is a nerve ending that's job is to detect certain stimuli.

Touch,

Temperature,

Pressure,

Stretch,

These types of stimuli are detected by a certain type of receptor.

There's tons and tons of different types of receptors in the body and they're constantly sampling our environment for different things.

We have receptors in our eyes,

They're called rods and cones.

These are what we see with,

We see color,

We see definition with these rods and cones.

In our skin,

Our muscles,

Our tissue in the more musculoskeletal part of the body,

These receptors are what we would classify as more,

There's two types of them specifically,

There's mechanoreceptors and nociceptors.

Within those two categories,

There's several other receptor types and we won't get into the specifics of them there,

But knowing that these nerve endings,

These receptors are what are interfacing with our world and when they are stimulated,

That's what kicks off an action potential and sends information up to the brain.

So,

Action potential.

An action potential is an electrical stimulus that travels along the length of the nerve all the way to an axon where it synapses with another nerve or reaches its final destination in the brain and we're going to go over a synapse here in a second.

An action potential is what we would consider an all or nothing stimulus.

So,

If a receptor is stimulated,

If I touch my skin,

A crude touch or maybe a fine touch receptor is going to,

If stimulated to a proper threshold,

Send a message to my brain that the skin on the back of my hand is being touched.

That action potential is only triggered if a certain threshold of stimulus is reached.

So,

That action potential,

Once sent,

It is detected by a,

So a stimulus hits a receptor,

Receptor decides and if it has a high enough threshold,

It kicks off the action potential from the dendrite,

Goes all the way through the nerve cell,

All the way to the other end to an axon.

The axon is the end of the action potential for that nerve.

Then what happens,

Because there isn't one single nerve that goes from fingertip to brain,

It has to synapse.

It has to create a junction and create a relationship with another nerve before it can continue on its journey up towards the brain.

So,

Then what happens is we have the synapse.

Another image here.

So,

If this is the axon here,

We've got the axon terminal,

The end of the axon,

This on this side is our dendrite for the next nerve that it's trying to reach and in the middle we have something called the synaptic cleft,

Which is basically a little space where a certain message transmission happens between these two nerve cells.

So,

Action potential comes along,

That electrical stimuli reaches the end of the nerve here and you can see these little bulbs at the very end here.

They're called synaptic vesicles and these synaptic vesicles are basically little bubbles where neurotransmitters live.

Neurotransmitters are little chemicals that are in all the little synaptic junctions in our body that are responsible for continuing certain messages and then propagating those messages onward.

There are tons and tons and tons of different neurotransmitters in the body and they have all sorts of weird and wonderful functions.

We won't get into them specifically,

But if you've heard the words dopamine and serotonin,

Those are types of neurotransmitters and they all have different jobs,

Different functions.

Depending on what type of neurotransmitter is being released,

You're going to have a different response in the body.

Anyway,

Back to our image here.

So,

Action potential reaches the end of the axon here and then if that action potential is meant to continue onward,

It will stimulate an opening of what we call here a voltage-gated calcium ion channel and it opens up and then allows the release of our neurotransmitter molecule across the synaptic cleft.

As those molecules reach the other side,

So a new dendrite of another nerve cell,

They're going to land in a certain type of receptor.

So,

Once the molecule matches with the appropriate receptor on the other side,

It will then kick off its own action potential and continue upwards.

So,

Really common junction places in the body are where nerve cells meet the spinal cord,

Where the spinal cord meets the brain,

And then there's several other relay centers in the brain where there's lots and lots of nerves that are having synapses and continuing messages along.

For the most part,

That is how the nervous system functions in a very basic nutshell.

And thanks again so much for listening.