We can think of the nervous system as split
up into two other parts.
There's going to be an autonomic nervous system branch.
And as the name kind of sounds like,
this is your automatic control.
That's the involuntary parts that we
talked about from above.
Beside that, there's also going to be a control that we exert.
And so that's going to be called the somatic nervous system.
So that's something that we control,
somatic nervous system.
Underneath the autonomic classification,
you can break this up into two other parts.
One is called the sympathetic nervous system.
And we sort of alluded to that above when
we were talking about the sympathetic ganglia that
were part of involuntary control.
In addition, we also have a parasympathetic nervous system
that sort of sits in a checks-and-balances position
with the sympathetic nervous system.
And that's how we break this up.
The somatic nervous system is just
the somatic nervous system.
So it has just sort of one function,
and it's trying to control voluntary muscle.
So the neurotransmitter that we use here,
which you may recall-- and I'll put this in parentheses--
is acetylcholine.
And we abbreviate that ACh for acetylcholine.
What about the neurotransmitters that
are used by the sympathetic and the parasympathetic nervous
system?
We actually sort of know them already,
at least for the sympathetic nervous system.
And we can come up with it.
And the way you know them is if you think about what
the sympathetic nervous system does.
Because I'm sure you've heard of this phrase called your fight
and flight response.
Fight or flight.
And so that's when you're in a dire situation and your body
senses, uh-oh, I may die at any second now.
I need to do something to get out of here.
And so you activate the sympathetic nervous system
so that you can achieve fight or flight.
You start pumping adrenaline through your body,
and you get your heart to beat faster
so you can pump more oxygen to your legs
to help you run quicker and get away.
So that's fight or flight.
And so I mentioned adrenaline, which
is an endocrine hormone that's secreted to help with this.
But it also has a neurotransmitter friend
that does the same thing.
And so the neurotransmitter friend
that I'm going to write up here, it's not adrenaline,
but it's noradrenaline.
Starts with an N. And another term for that
is norepinephrine.
I'll write it out.
Norepinephrine.
Or noradrenaline.
And so that's the neurotransmitter
that's used by the sympathetic nervous system.
What about the parasympathetic nervous system?
Well, oddly enough it actually uses the same one
that the somatic nervous system does.
And the way that you can sort of differentiate this
from the sympathetic nervous system
is that, while the sympathetic nervous system is
for the super, hardcore, intense moments where
it's fight or flight, the parasympathetic nervous system
is a little more chill.
This is for rest and digest.
So when you're going to sleep and you're trying to relax so
your heart rate can lessen and your muscles and your heart
aren't contracting as quickly.
Or if you just ate a big meal and you
need to digest that food, the parasympathetic nervous system
will tell the stomach to churn that food up
so you could digest it in your intestines
as you also propel it along with the smooth muscle in there.
So that's achieved by acetylcholine.
All right?
So that's the two major divisions
of the central nervous system, autonomic and somatic.