00:01
So let's look more specifically
at the neuromuscular junction.
00:04
This is the connection between
the nerve and the muscle.
00:07
Where the body says,
I need to move
and the muscle
makes that happen.
00:11
And we're an electrical signal is
converted to a chemical signal
that drives muscle depolarization.
00:16
There's a lot of things
that happen in this area.
00:19
And the key things that
I want you to understand
is that we see
an action potential
which is an electrical signal
converted into a chemical signal
through acetylcholine,
which is a neurotransmitter.
00:30
This binds to the
acetylcholine receptor
and drives muscle contraction.
00:35
As a result, we can see problems
that develop in each area
of the neuromuscular junction.
00:40
Some disorders affect the
presynaptic terminus of the nerve.
00:44
And we see certain characteristic
symptoms and signs
as well as results
to testing.
00:49
Other conditions
are going to affect
the postsynaptic terminus
of this junction,
and present accordingly.
00:56
So let's look more specifically
at the biology of the
neuromuscular junction.
01:00
What happens to allow
muscles to move?
The first thing is that an action
potential travels down a nerve
to the presynaptic terminus.
01:09
As a result of the activation
from the action potential
calcium channels recognize
that influx of sodium
and are activated.
01:19
Calcium moves into the
presynaptic terminus
from Voltage-gated
calcium channels,
and those channels
are going to be important
for certain disorders.
01:28
Calcium influx is sensed by
the synaptic vesicles
containing acetylcholine,
and the presynaptic terminus
and those vesicles then bind
to the presynaptic membrane.
01:40
Acetylcholine is released
into the synaptic cleft,
And this is what does the action
at the neuromuscular junction.
01:47
Acetylcholine binds to the
acetylcholine receptors
on the muscle membrane.
01:53
Importantly,
acetylcholinesterase enzymes
are present in the synaptic cleft
to break down acetylcholine
and recycle that function
at the neuromuscular junction,
so the another action potential
can drive activation.
02:06
On the postsynaptic membrane,
we see acetylcholine receptors.
02:12
When binding of acetylcholine to the
acetylcholine receptor occurs,
there's a sodium influx
into the muscle
and this drives
muscle contraction.
02:21
So that's the normal process,
and break down
at the presynaptic terminus
or postsynaptic membrane
will cause problems
with muscle function
and present with weakness.