Voiceover: In this video I want to just introduce some
of the anatomy involved in neurotransmitters.
Recall that neurotransmitters are molecules
that communicate between neurons
and their target cells and chemical synapses.
And some neurotransmitters are released by neurons
distributed widely throughout the nervous system,
while others are specific to certain areas.
For examples of some neurotransmitters
that are released by neurons distributed
throughout the nervous system, the first one is glutamate,
which is the most common excitatory neurotransmitter
of the entire nervous system.
Then there's GABA, which is short
for gamma-aminobutyric acid, and glycene,
and these are the most common inhibitory neurotransmitters
of the nervous system, GABA in the brain
and glycene in the spinal cord in particular.
Neurons releasing these neurotransmitters
are widely distributed through the nervous system,
and these neurotransmitters are really involved
in most functions of the nervous system.
Next I want to just introduce some
of these areas of the brain that have collections
of neurons that send axons diffusely
to release specific neurotransmitters
onto widespread areas of the cerebral cortex.
And often other areas as well,
but these widespread projections to the cerebral cortex,
let me just represent these by a few axons
coming up toward the cerebral cortex,
and these widespread projections that are dumping
a bunch of a specific kind of neurotransmitter
all over your big areas of the cerebral cortex
are really important for a bunch
of the higher functions of the nervous system,
including the cognition, emotion, and consciousness.
So let me start introducing a few of these,
and I'm going to start with glutamate,
because there are specific areas
in the reticular formation of the brain stem
and parts of the thalamus that project axons diffusely
up to the cerebral cortex and release glutamate
all over neurons of the cerebral cortex.
And this collection of neurons
that has this diffuse projection
of glutamate to the cerebral cortex,
we call this the reticular activating system.
And this is actually required for consciousness.
Without this system, there usually is no consciousness.
The next one I want to mention is acetylcholine.
There are certain nuclei in the frontal lobe
that actually send diffuse projections up to a number
of areas in the cerebral cortex, releasing acetylcholine.
These are called the basalis nucleus and the septal nuclei.
The next one I want to mention is histamine,
and there are a number of neurons in the hypothalamus
that send projections to release
histamine all over the cerebral cortex.
So the hypothalamus is here, and these neurons
send these diffuse projections up
to the cerebral cortex to release histamine.
Next is norepinephrine, and there's an area
here in the pons where there are a bunch
of neurons that send diffuse projections
of norepinephrine up to the cerebral cortex.
That area is called the locus ceruleus,
and I've seen a few different ways of spelling this,
but this is the one I'm familiar with.
I'm sure any of them are fine.
Then there's serotonin, and there are a number
of nuclei at all levels of the brain stem,
up here in the midbrain, down here in the pons,
and in the medulla that are all called the raphe nuclei.
These raphe nuclei release serotonin,
and my understanding is that it's mostly the ones
that are higher up that send diffuse projections
up to the cerebral cortex to release serotonin,
and that these raphe nuclei also send serotonin
to other part of the nervous system.
And last up, although I'm sure there's probably more,
but last up that I want to talk about
of these diffuse projection systems
releasing neurotransmitters onto the cerebral cortex,
involves the neurotransmitter dopamine.
For dopamine, there's an area here-ish in the midbrain
that diffusely projects dopamine onto the cerebral cortex,
and that area is called the ventral tegmental area.
I'll just right VTA for short
for the ventral tegmental area.
So all of these diffuse projection systems
sending neurotransmitters through widespread areas
of the cerebral cortex are, again, very important
to the higher functions of the nervous system,
like aspects of cognition and emotion and consciousness,
and many psychiatric disorders appear
to involve dysfunction of these neurotransmitter systems.
Many of the psychoactive medications appear
to influence neurotransmitter release from these
diffuse projection systems to the cerebral cortex.
Now, for dopamine in particular,
there are a couple of other projection systems
of dopamine that aren't to the cerebral cortex,
but that are important for functions of the nervous system
and can become problems for medications
that affect dopamine neurotransmission.
One of these is right next to
the ventral tegmental area in the midbrain.
I'll actually draw them overlapping
because they're so close together.
And it sends axons releasing dopamine
to a couple of nuclei deep in the cerebral hemisphere,
and these are all actually parts of the basal ganglia.
So this collection of neurons in the midbrain
that is projecting dopamine is called the substantia nigra.
It's actually projecting dopamine up
to another part of the basal ganglia called the striatum.
If there's some problem with this system,
some problem with the substantia nigra
getting dopamine to the striatum,
that appears to be what happens with Parkinson's disease.
I won't go more into that now,
but that's very important for Parkinson's disease
and other disorders that have Parkinsonism,
or the symptoms and signs of Parkinson's disease.
There are also dopaminergic neurons in the hypothalamus.
These dopaminergic neurons in the hypothalamus
are actually sending dopamine down
to the pituitary gland to control the release
of one of the hormones in the pituitary gland.
I won't go any more into that,
but that's another important dopamine projection system.
So all of that's in the central nervous system
in the brain and the spinal cord,
but there are neurotransmitters involved in the function
of the peripheral nervous system too, all the nerves
going out to structures in the rest of the body.
Our main ones there are acetylcholine and norepinephrine.
Acetylcholine has several jobs.
It's the neurotransmitter released
from lower motor neurons coming out of the spinal cord
or the brain stem, and their axons will then synapse
on skeletal muscle cells and release acetylcholine,
that's the neurotransmitter they use.
But acetylcholine is also involved
in the function of the autonomic nervous system.
Let me just write ANS for short
for autonomic nervous system.
Most of the neurons of the autonomic nervous system
release acetylcholine as their neurotransmitter,
and a smaller number of neurons
of the autonomic nervous system
release norepinephrine as their neurotransmitter.
So I'll stop there in my overview of the anatomy
of neurotransmitters to just give you a feel
for how many different types of neurotransmitters
are located in lots of different areas.
And I just want to make the point
that some neurotransmitters are used widely
throughout the nervous system, whereas others
have these more kind of discrete collections of neurons
that are either projecting widely to areas
of the nervous system like the cerebral cortex,
or more specifically between one specific area
and another specific area.