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Printable Handouts
Navigable Slide Index
- Introduction
- Anatomy of a nerve cell (neuron)
- Central nervous system synapse (neuron to neuron)
- Stop and think: question 1
- Types of neurotransmitters (broad)
- Types of neurotransmitter receptors (broad)
- Some common neurotransmitters
- Stop and think: question 2
- Neuromuscular junction (neuron to skeletal muscle cell)
- Stop and think: question 3
- Stop and think: question 4
- Synaptic input
- Initiation of action potential in a neuron
- Graded potentials decrease in size as they move away from the synapse
- The further a synapse is from the axon hillock, the less impact it will have
- The effect of distance
- Spatial summation
- Temporal summation
- Bringing the axon hillock to threshold
- EPSPs and IPSPs can interact
- Which motor neuron will generate an action potential first?
- Graded potentials vs. action potentials (simplified)
Topics Covered
- Types of neurotransmitters and their receptors
- Action potentials
- Graded potentials
- Synaptic transmission
- Neuromuscular junction
- The distance from axon hillock
- Spatial summation
- Temporal summation
- EPSPs and IPSPs
Links
Series:
Categories:
Therapeutic Areas:
Talk Citation
Sevigny, C. (2023, January 31). Synaptic transmission and graded potentials [Video file]. In The Biomedical & Life Sciences Collection, Henry Stewart Talks. Retrieved December 3, 2024, from https://doi.org/10.69645/CPNZ1131.Export Citation (RIS)
Publication History
Financial Disclosures
- Dr. Charles Sevigny has not informed HSTalks of any commercial/financial relationship that it is appropriate to disclose.
Other Talks in the Series: Fundamentals of Human Physiology
Transcript
Please wait while the transcript is being prepared...
0:00
Hello, and welcome back to
fundamentals of
human physiology.
I'm Charles Sevigny.
We're going to continue
our discussion
today about how
neurons function.
0:11
So far we've learned about how
excitable cells maintain
a membrane potential.
Meaning that there is the
potential there for ions to move
across the membrane and actually
affect the charge
in that membrane.
We learned how that works in
the context of action
potentials through
voltage-gated channels
and how those
are conducted across an axon.
Today, we're going to address
a few things that we left
as a mystery before.
So far all we've learned is that
an action potential begins
at the axon hillock here,
travels down the axon.
The things we'll focus
on today is what
happens when it reaches
the end of the axon,
that's called synaptic
transmission.
How does it actually take
that electrical signal
and translate it
into something that
the next cell can recognize?
We need to translate
an electrical signal
into a chemical signal.
We'll talk about that. The
other thing we'll discuss is
how do we actually start
this action potential?
How does a neuronal
cell body manage
various inputs from
all these different synapses
to decide whether or not
it's going to form and
initiate an action potential?
1:12
Let's start with
synaptic transmission.
If we zoom in on one of
our synapses here and we
just need to get some nomenclature
under our belts first.
The cell in which we have
our action potential
traveling along,
so the first neuron, that's
called the presynaptic neuron,
the one before the
synapse and the cell
- it might be a neuron,
in this case it is,
but it could be by a
gland or a muscle or
whatever - is called
the postsynaptic cell.
Because we have
neurons here, we'll
call it the postsynaptic neuron.
We actually have a very
elaborate structure
here in the synapse.
There's a lot of things
that aren't shown here.
We're going to give a
very simplified overview
of how synaptic
transmission works,
because otherwise
there's literally
an entire course
on how this works.
Forgive me if I don't go
into all the details,
but we'll go over the general
idea of how this works.
What we have is we know we have
our action potential traveling
down our presynaptic neuron,
and that's a depolarizing
signal. What happens?
The first thing that
happens is that
that action potential
encounters a new type
of voltage-gated channel called
the voltage-gated
calcium channels.
Predictably, that causes
calcium like we learned before,
that calcium has a big drive
to want to move
inside our cells.
It has a very positive
equilibrium potential,
meaning that even though
this cell might be at
plus 30 because it's in
the middle of an
action potential,
calcium will still want to
move in through those channels.
That's what makes calcium such
a powerful signaling chemical.
Because no matter what really
is happening in this cell,
no matter how positive it gets,
it has such a high
equilibrium potential,
it will still want to
move into the cell.
Now, what's happening
inside the cell?
Inside the cell we have
these things called
synaptic vesicles.
They're basically little
power packets made out of
similar stuff that the cell
membrane is made out of.
But inside these synaptic
vesicles we have
a very high density
of neurotransmitter.
We'll talk about specific
neurotransmitters in a bit.
For now we have our
neurotransmitter
packed in these
synaptic vesicles.
Very high density, and
that tells us something.
That in the walls of
these synaptic vesicles,
we must have some
transporter using
ATP and active transport to
package our neurotransmitter in
there in such a
high concentration.
What happens is when calcium
moves into the cell,
we have a "series of events."
This is where I'm skipping
over a lot of detail.
But what's going to happen
is that these vesicles will
'dock' with the cell membrane
here right at the terminal.
When they dock,
that membrane fuses
and they open up, as
you can see here,
so that our neurotransmitter
floods out into
this area between our two cells
called the synaptic cleft.
That's great because
now we have a chemical,
we've translated our electrical
signal into a chemical one.
We've sprayed this
neurotransmitter
out into the synaptic cleft.
But it's not going to do
anything there unless
we have something
to recognize it.
That's why importantly,
on the other side
of our membrane,
on our postsynaptic
cells, we have receptors.
Many of these are
ligand-gated channels,
and by ligand we mean
a chemical that comes
into contact with them.
We had voltage-gated
channels before that were
shut and open when we
have a change in voltage.
These are gated channels
that are shut and open
when they come in contact
with their neurotransmitter.
We're going to talk about those
in a little bit more detail.
Depending on what ion those
channels allow through
will depend on the effect
on the postsynaptic neuron.
Let's say this channel
here allows sodium
to move through.
Our neurotransmitter comes,
it opens the channel,
sodium then moves into the cell,
and that depolarizes the cell
locally on the other side.
We'll talk about
that a little bit
more as we move through.
The next thing that
we need to deal
with is now we have all
this neurotransmitter
here and we don't want it just
continually activating
these receptors.
We want to be able to
fire an action potential,
have that neurotransmitter
there and then clear it out,
so that we can be very specific
with the signal that
we're trying to transmit.
Now, we clear that out
in two different ways.
One, we'll have reuptake
transporters in
the presynaptic
cell that will suck
that transmitter back
up into the cell.
Depending on the
neurotransmitter,
these reuptake
transporters work in
different ways, and
sometimes some drugs
actually interfere with
this so that we actually
have a buildup of
neurotransmitter in that synapse.
We'll talk about
that in just a bit.
We might have enzymes
here that are actually
actively metabolizing
these neurotransmitters.
There are also
other cells within
our central nervous system
called glial cells,
that also serve to mop up some
of this excess neurotransmitter
that might build up there.
But either way, we know that
we're releasing the
neurotransmitter,
it's activating our receptors
in the postsynaptic cell,
then we're clearing it out
through a variety of means.
That's how a regular
synapse works
and how synaptic
transmission works.