So let's start off with
cranial nerve I.
This is the olfactory nerve.
And while historically, we haven't paid
as much attention to the olfactory nerve,
I think the COVID-19
pandemic brought to light
the fact that there are certain conditions
that do compromise the olfactory system.
And COVID-19 virus had a
predilection for causing a nausea.
So it's useful to at the bedside
quickly assess for olfaction.
A simple test at the bedside is
simply to use 2 or 3 common sense.
And for me,
I'll oftentimes use the following.
Alright, so Shawn,
I'd like you to do is to close your eyes
and occlude your right nostril.
What do you smell?
Alcohol, for sure.
now occlude your other nostril.
What do you smell?
Simple bedside test of
the olfactory system.
Alright, so now let's move on to assessing
the second cranial nerve, the optic nerve.
For the purposes of the neurologic
exam that we're covering here,
we're going to be doing
peripheral field testing,
basic vision using
a snellen chart.
And we'll also look at the
pupillary afferent input.
we're looking at the third cranial nerve.
So first off,
we want to assess grossly,
can this person see or not?
And so we use our
handy snellen chart,
I'm going to have
you stand over there.
The snellen chart can be,
you know, kept in your pocket.
And it's easy enough to use,
you want the patient to be
about 6 ft away from the chart.
And I'm going to have you
cover up your right eye.
You can have a patient do this with
glasses and then without glasses,
depending upon the clinical circumstances
that you're doing the assessment in.
And I just want you
to start around here
and tell me the letters that
you can read from right to left.
O - L - C - F
Great, let's skip
down to the down here.
E - P - T - Z - L
I would have him cover up his left
eye and do the exact same thing
and want to mark based
on the snellen chart
exactly what level of visual
acuity that the patient has.
It can also usually
with the snellen chart
will include some color
testing as well as needed.
And also there's a nice
pupillary gauge on here
for when we get to the part
of assessing pupillary size.
Please have a seat again, Shawn.
Now we're going to do
visual field testing,
which is actually a very useful skill
in terms of its likelihood ratios
for detecting an actual visual
field cut on peripheral testing.
But at the bedside,
we can do a very good job.
So what I'm going to do is have you
again cover up your right eye.
And I want you to
look at my nose.
And the way that I do this,
I'm just going to have you tell me
whether the upper hand is moving
or the lower hand is
This is called kinetic visual field
testing because I'm moving something.
Very simple testing,
very easy way to do that.
And you can move in slowly
if you're finding the patient
is not detecting things
in just those quadrants.
But that's a quick and dirty way
to assess visual field problems.
And of course, I would have
him do the other side as well.
The next component of assessing the
optic nerve is again pupillary size,
and we'll jump into doing that.
Now keep in mind that
the afferent input
for pupillary constriction
is the second cranial nerve.
But the efferent pathway which actually
involves pupillary constriction happening
is mediated through your
third cranial nerve.
So let's take a look at that.
So for starters,
you of course want to dim the lights
when you're trying to
assess pupillary size
so you can maximally
have the pupils dilated
so you can best see them react
when you expose them to light.
So first off, we're just going
to have you look over here.
I'm looking at one pupil,
looking for constriction.
Looking at the other pupil,
looking for a good constriction.
I would document my exam that the
pupils are going from 4 mm to 2 mm.
You want both numbers,
both before you put the light in
and then after you've
exposed them to light.
And then an important test is
the swinging flashlight test.
This is to test for
a Marcus Gunn pupil
also known as an afferent
Oftentimes seen with, for example,
optic neuritis from multiple sclerosis
where the input from the optic nerve
is not being collected in one eye.
And so there's no afferent information
going back to the brain in one eye,
but the efferent information from the
third cranial nerve is functioning.
So if I shine light in this eye,
not only does this I constrict
but this one does as well
and that's completely normal, that's
called the consensual pupillary response.
If I go back to this
eye on the right,
where there's no afferent
information it would actually dilate
as this eye was relaxing and
not getting input anymore.
So that's a classic sign
of a Marcus Gunn pupil.
The last thing to take note of
when you're looking at the pupils
is the pupillary symmetry
between one eye and the other
folks with anisocoria which is where
one pupil is larger than another.
It's typically mediated
by the third cranial nerve
due to problems with sympathetic
or parasympathetic input
to the pupillary
if that's not the problem
that's causing anisocoria
a so-called surgical pupil
is where one pupil is a different
size or even a different shape.
It's not quite a full circle
if they've had cataract surgery
or some other kind of surgery.
And it's nothing to be alarmed
about if there's a known history
and if it's been
documented in the past.
Alright, so we've already started
testing the third cranial nerve
while we were assessing
and we talked about an
afferent pupillary defect
versus a problem with parasympathetic
or sympathetic information
through the third cranial nerve.
Now we're going to look at the
role of the third cranial nerve
in terms of ocular
And this is of course
going to also include
the fourth cranial nerve
and the sixth cranial nerve
since all three of them mediate
movement of the eyeball.
The sixth cranial nerve just to
start off with is the abducens nerve,
and that is operating the
lateral rectus muscle.
The fourth cranial nerve
is the trochlear nerve
and that's operating the
superior oblique muscle
and then the third cranial nerve mediates
all the other movements of the eye.
So the superior and
the medial rectus and
the inferior oblique.
So to test those things,
we'll start off by having
you just look at my nose
and just follow my
finger with your eyes.
So having said that,
we'll move on to the fifth cranial nerve,
the trigeminal nerve.
Now, I always get mixed up
with which nerve
is the fifth cranial nerve,
because the trigeminal nerve, the sensory
input for the face is called V
one, v two and V three.
And so I hear the letter V and I start
thinking about the vagus nerve.
But the V refers
to the Roman numeral five,
so it's Roman numeral five, section one,
section two, and section three.
So always the nomenclature can can
throw me off as much as anybody else.
So the trigeminal nerve has sensory
and motor function.
The sensory function I've just alluded to
V one is the ophthalmic
branch of the trigeminal nerve.
Then we have a maxillary branch
and then a mandibular branch,
and you can simply test for those
for the function of that nerve as follows
You feel me on both sides?
Does it feel the same on both sides?
So that's the testing for V one, v two
and v three of the trigeminal nerve
and then motor function.
The trigeminal nerve works on the master
muscle and the triggering muscles.
Clench your teeth good.
I should be able to feel
his temporal muscles up here
and the mass of the muscles which are
keeping his his bite nice and tight.
And then I want you
to move your jaw side to side.
So those are the triggered muscles.
And so by
showing evidence that his jaw can move
and then he can have a tight clenched jaw,
it tells me that his trigeminal nerve
motor function is functioning.
completed the fifth cranial nerve,
we already talked about the sixth
So we're now moving on to the seventh
The facial nerve.
The facial nerve has motor sensory and
even autonomic nervous system function.
But the only parts
that we can really assess on
physical exam is the facial function.
So let's jump into that.
The facial nerve
when it exits, just interior to the ear
and goes to the product gland.
There's a number of different branches
working on different muscles in the face.
Even before it exited interior to the ear,
it went off and innervated
the speed's muscle within the middle ear.
So to test the facial nerve,
I'm going to have you first.
Lift up your eyebrows.
Great. That's testing the frontal
US muscle vigorously.
Lift up your eyebrows. Great.
Now close your eyes really tightly.
This is the optic hilarious
axillary muscles that are going to
have him puff out his cheeks.
And don't let me push them. Perfect.
And now have you smile. Great.
So this is a quick way to test
for the different
innovations of the facial nerve
to the muscles of the face.
who have a peripheral lesion
with a facial nerve palsy,
the classic one being Bell's palsy,
will have weakness
to the entire half of their face.
In contrast, a patient who's had a stroke,
it turns out that the front
is duly innervated by both hemispheres.
So if you had a stroke on the left,
yes, you'll have weakness
on the left side of your face.
It's the stroke was on the right side
of your in your right cerebral cortex.
But because the left cerebral cortex
also innovates the frontal us muscle,
you would still have intact movement
of the frontal us muscle.
So that can be a telltale sign to identify
a central lesion versus
a peripheral lesion.
And of course, those are very different
approaches that you'll take based on
which of those you've you've identified.