Alright, so there are a couple of dimension in which I would hope that you
would use this table in your studies. We've been emphasizing the horizontal
dimension, that is looking, one nerve at a time.
Thinking about what are the various components that we would find in that
nerve, so that's one way to approach using this table.
Another would be the vertical dimension and that is to think about okay, what are
the Somatic motor components in the brain stem.
And just think about the nerves, think about their anatomy.
How they attach to the brain stem, and I would suggest that you do so thinking from
superior to inferior. All right, so, march through each column
that way, the Somatic motor, the Branchial motor, the Visceral motor.
And then on the sensory side, think about taste, how is taste conveyed to the brain
stem. And so on.
And I think you'll find that this table is not quite as daunting as it might first
appear. Well that's good because when we get to
the actual anatomy of the nuclei in the brain stem that connect to these nerves.
It will seem a bit overwhelming so I might ask you to brace yourself for that but we
can get through that together. And hopefully this chart in front of you
will be one way to organize your understanding of these nuclei by name and
by location as well as by function. Okay, well, I'm going to try to simplify
this for you just a little bit. Borrowing a scheme that I've learned from
my colleague here at Duke Doctor[UNKNOWN]. Doctor[unknown] suggest that we can think
of the cranial nerve as being related to 16 cranial nerve nuclei.
And these 16 nuclei can be grouped into 4 groups of 4.
So it's sort of 4x4 equals 16 perspective on the cranial nerve nuclei.
So 16 cranial nerve nuclei that are sub divided into 4 groups of 4.
3 of these groups are motor nuclei. So that accounts for 12 of the 16 nuclei.
There are 4 Somatic motor nuclei, 4 Branchial motor nuclei and 4
Parasympatheic motor nuclei to talk about. Well, that accounts for 12 of the 16 so
that must mean that there is one group that's sensory nuclei and actually that
group can be subdivided further according to the chart we saw on the previous slide.
But to make this 4x4 frameworks stick, I think it might be helpful just to avoid
thinking about that subdivision at the moment.
And consider 4 groups of 4 nuclei. 3 motor and then 1 group of sensory
nuclei. Okay, now let's see how that 4x4 scheme
maps now onto this chart where we've just gone through the cranial nerves that
attach to the brain stem and identify the function associated with each.
So what we're going to do is talk about the nerves, but we're going to deal with
them one column at a time. Okay?
So let's go ahead and, and do so. The 3rd nerve conveys Somatic motor output
to muscles in the orbit that moves the eyes, as I suggested.
And that outport is coming from a nucleus called the ocular motor nucleus.
The next Somatic motor nucleus that we encounter is just a little bit inferior in
the caudal part of the mid-brain, and that's associated with the 4th nerve,
called the trochlear nerve. So, 2 Somatic motor nuclei in the
mid-brain. Oculomotor superior and trochlear just
inferior. Now, the next Somatic motor nucleus we
have in the caudal pons and it's associated with the 6th nerve.
It's the abducens nucleus. And then, the final Somatic motor nucleus,
the 4th of that first group is down in the medulla.
In the upper part of the medulla associated with the roots of the 12th nerve and it
is called the Hypoglossal nucleus. So there is our first group.
There is our first 4 nuclei associated with somatic motor control.
Now for Branchial motor, we have the tri-germinal motor nucleus.
It's the motornucleus that grows out, the motoraxons and the trigeminal nerve and
this supplies to motor output to the muscles of chewing or mastication.
The 7th nerve the nucleus there is called the facial nucleus.
And that nucleus is responsible for governing the muscles of facial
expression. Okay, so far so good.
We've identified six cranial nerve nuclei. And the names of these nuclei all match
the nerve that they contribute. That they contribute to.
Well, that won't always be the case as we're about to see.
The Branchial motor component in nerves 9 and 10 comes from a nucleus appropriately
named called the nucleus ambiguus. It's very difficult to see in our standard
histological preparation of the brain stem which resembles a myelin stain.
Of course if we stained for the presence of cell bodies, especially for motor
neurons, we'd see the nucleus ambiguus quite clearly.
But usually, histologists look at myelin stain sections of the brain stem, and it's
quite obscure. So that's the nucleus ambiguus supplying
Branchial motor outflow through nerves 9 and 10.
The Branchial motor outflow through nerve 11 comes from the accessory nucleus in the
upper cervical segments of the spinal cord.
Alright, what about the four parasympathetic nuclei?
Well, beginning with nerve 3, there is a contribution that is responsible for the
constriction of the iris. That comes from a nucleus called the
Edinger Westphal which sits just superior and a little bit lateral to the ocular.
The motor nuclei up in the mid-brain at the level of the 3rd cranial nerve.
The next place where we have parasympathetic outflow is associated with
nerves 7 and 9. And that outflow comes from a set of
nuclei that we call the salivatory nuclei. Now we could subdivide them into a
superior excuse me a superior and an inferior group.
But to keep this 4x4 scheme going, we'll just collectively consider them the cell
of a toy nuclei. Okay, well, the next major parasympathetic
outflow to consider comes from 2 nuclei. A division of the nucleus ambiguous, which
is separate from the one that provides Branchial motor outflow.
This division is responsible for the cardio inhibitory output that goes to the
heart from the vagus nerve. Well, the other major parasympathetic
outflow to consider in the vagus nerve comes from a nucleus called the dorsal
motor nucleus of the vagus nerve. Alright, well that accounts for our, three
groups of motor nuclei. So lets just make sure we've got more
here, so that's 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12.
Okay. So, we got three groups of four motor
nuclei. Alright.
Now on the sensory side. Okay.
We have 3 nerves in the brain stem that convey a sense of taste back in to the
central nervous system. The all supply the same nucleus, actually,
they supply the rostral division of the nucleus.
The caudal division of the nucleus is the recipient of the general visceral
sensations that are involved in regulating our cardiac rhythms, our blood pressure,
and our respiratory rhythms. And that nucleus is called the nucleus of
the solitary tract. Solitary tract is a very visually striking
tract. And the dorsal part of the tegmentum of
the medulla and there's a gray matter of nucleus surrounding it.
We call that the nucleus of the solitary tract.
So, notice there are two divisions of it and as I mentioned the rostral division is
concerned with taste. The caudal division is concerned with
visceral sensation. Our general somatic sensory system is
again conveyed via multiple nerves, but to, to one nuclear complex.
And that nuclear complex is the trigeminal nuclear complex.
Now when we get into our discussions of somatic sensation including
mechano-sensation and pain and temperature sensitivity.
We'll see that we can subdivide this trigeminal nuclear complex into 3 major
parts, but we won't get into that now. We'll just recognize this as one nuclear
complex. And then lastly, our Special sensory
nuclei in the brain stem include our cochlear nucleus and our vestibular
nuclear complex. Okay, let's see how we've done here with
our numbering scheme now. So we counted 12 motor nuclei here's 1
sensory nucleus, here's the 2nd sensory nucleus and then a 3rd and a 4th.
Okay, so we've accounted for our 4 sensory nuclei to add to our 12 motor nuclei,
giving us a total of 16. Alright, well I hope that scheme has
helped you. We have lots of different ways to assist
you in learning these nuclei and how to organize them.
One additional method is shown in a slide that comes from the textbook that you may
choose to read along with these tutorials. And this scheme is just a little bit
different from the one that I've showed you but it, it still basically lays out
subcategories for motor control and for sensation and shows you how the motor
nuclei can be arranged accordingly. Well I hope this has been helpful.
It's been sort of a whirlwind tour through the cranial nerves emphasizing their
functions. And then just giving you some handle on
how those functions can be related to the nuclei of the brain stem.
In a different tutorial, we'll actually see those nuclei.
And find them in histological sections. So, that will be forthcoming.
But before we get there see if you can't rehearse a little bit, in your own mind,
this 4x4 scheme for mapping the functions of the cranial nerves to the nuclei of the
brain stem. I'll see you next time.
