Here we’ll take a look at muscle pathology
but the focus here will be
the neuromuscular junction.
So please picture neuromuscular junction.
So we have a nicotinic receptor, and in
your head, you should be thinking about
the presynaptic terminal of the nerve
which is then communicating with
the motor end plate. In other words,
the skeletal muscle.
In that presynaptic termina l, we have a
vesicle and in that vesicle we have
So what are things that you’re
going to do to identify
[Inaudible 00:03:39] doesn’t mean all
receptors have been destroyed.
But what if there was a method
that you could test
and you activate those receptors?
If you activate those receptors, then maybe
perhaps you will find movement.
Keep that in mind. So the weakness
has intensified by use.
That’s important because you’re going to be
comparing myasthenia gravis with what?
Lambert-Eaton myasthenia gravis syndrome.
So here, in myasthenia gravis, with use,
it’s the patient that is feeling tired
and recovers upon rest
3 in 100,000 would be the epidemiology.
The prevalence, as I’ve told you, would
be much more in women
because of its autoimmune
nature—less than 40 years.
If it is a male, by chance,
affected greater than 60.
Pathogenesis. You have the
that are then attacking the
and surgically, there’s a possibility that
the thymus may then be removed
resulting in a thymic remnant.
And by doing so,
you are now actually improving the
patient’s signs and symptoms.
So the thymus is [Inaudible 00:04:47]
to type 2 hypersensitivity,
[Inaudible 00:04:51] toxicity,
try and go after those
The pathology here [Inaudible 00:05:04]
that the type 2 muscle fibers
will be affected first.
What kind are these? Fast, white
ATPase—lots of it.
For example, the ocular muscles.
There is absent simplification
of the motor end plate,
what does that mean?
It means that the acetylcholine receptors
are being knocked out,
and depending as to the severity
of the disease,
you will still have residual
[Inaudible 00:05:33] simplified.
Let’s go ahead and take a look at
that neuromuscular junction.
On the left, is normal.
So what is that that you see here?
The bulb which is coming down?
The bulb that you see coming down or the
flask, or whatever you want to call it,
it’s the presynaptic terminal,
and at the presynaptic terminal, you’ll
then notice you have these vesicles.
Inside those synaptic vesicles, of course,
is your acetylcholine.
What then allows for the vesicle to fuse
with your presynaptic membrane?
Help me out here.
Good. Voltage-gated calcium channels.
So the voltage-gated calcium channels
where are they located?
Not on the bottom structure—the bottom
structure, what is that?
That’s your motor end plate.
What does that mean?
That’s your skeletal muscle .So we’re
trying to have movement—motor end plate.
So the voltage-gated calcium
channels are on the
the presynaptic terminal, on the flask,
but then opens up the calcium channel.
Voltage coming from where?
The axon up above.
So the action potential is going to
come down the axon,
come down through the
presynaptic terminal and then open up
that voltage-gated calcium channel.
The calcium, of course, rushes in
allowing for fusion of the synaptic
vesicle that you see there.
With the membrane, and out then comes whom?
That acetylcholine is then going to bind to
the acetylcholine receptor and
open up what kind of channel?
[Inaudible 00:07:14] sodium channel.
The [Inaudible 00:07:16] acetylcholine
and the receptor, of course,
being on the skeletal muscle.
That’s normal on the left.
So what happens in myasthenia gravis
syndrome on the right?
You’ll notice autoantibodies
with the thymic hyperplasia
thymoma that is indicated
and these are antibodies are then going
to attack acetylcholine receptors,
So that, all important.
Junction in communication between
when it’s not happening, you’re
not having a contraction.
What type of muscle fibers
will be affect first?
Type 2, your fast-twitch. I gave you
the ocular muscles.
And what to test that you
may want to provide
or administer so you can find
increase in strength?
So what if you were able
to give a short-acting
such as edrophonium
in which you increased the concentration
of acetylcholine in that cleft?
It’s possible that the acetylcholine
might then linger around
and find a receptor that may
Then giving you for that
brief moment in time,
when you’re given that drug,
an increase in strength,
and by doing so, you’ve confirmed
myasthenia gravis. Haven’t you?