Medical Neuroscience explores the functional organization and neurophysiology of the human central nervous system, while providing a neurobiological framework for understanding human behavior. In this course, you will discover the organization of the neural systems in the brain and spinal cord that mediate sensation, motivate bodily action, and integrate sensorimotor signals with memory, emotion and related faculties of cognition. The overall goal of this course is to provide the foundation for understanding the impairments of sensation, action and cognition that accompany injury, disease or dysfunction in the central nervous system. The course will build upon knowledge acquired through prior studies of cell and molecular biology, general physiology and human anatomy, as we focus primarily on the central nervous system. This online course is designed to include all of the core concepts in neurophysiology and clinical neuroanatomy that would be presented in most first-year neuroscience courses in schools of medicine. However, there are some topics (e.g., biological psychiatry) and several learning experiences (e.g., hands-on brain dissection) that we provide in the corresponding course offered in the Duke University School of Medicine on campus that we are not attempting to reproduce in Medical Neuroscience online. Nevertheless, our aim is to faithfully present in scope and rigor a medical school caliber course experience. This course comprises six units of content organized into 12 weeks, with an additional week for a comprehensive final exam: - Unit 1 Neuroanatomy (weeks 1-2). This unit covers the surface anatomy of the human brain, its internal structure, and the overall organization of sensory and motor systems in the brainstem and spinal cord. - Unit 2 Neural signaling (weeks 3-4). This unit addresses the fundamental mechanisms of neuronal excitability, signal generation and propagation, synaptic transmission, post synaptic mechanisms of signal integration, and neural plasticity. - Unit 3 Sensory systems (weeks 5-7). Here, you will learn the overall organization and function of the sensory systems that contribute to our sense of self relative to the world around us: somatic sensory systems, proprioception, vision, audition, and balance senses. - Unit 4 Motor systems (weeks 8-9). In this unit, we will examine the organization and function of the brain and spinal mechanisms that govern bodily movement. - Unit 5 Brain Development (week 10). Next, we turn our attention to the neurobiological mechanisms for building the nervous system in embryonic development and in early postnatal life; we will also consider how the brain changes across the lifespan. - Unit 6 Cognition (weeks 11-12). The course concludes with a survey of the association systems of the cerebral hemispheres, with an emphasis on cortical networks that integrate perception, memory and emotion in organizing behavior and planning for the future; we will also consider brain systems for maintaining homeostasis and regulating brain state.
Cranial Nerve Nuclei, part 3
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Aus dem Kurs von Duke University
Medical Neuroscience
1233 Bewertungen
Aus der Unterrichtseinheit
Neuroanatomy: Internal Anatomy of the Human CNS
Treffen Sie die Kursleiter
Leonard E. White, Ph.D.Associate Professor
Department of Neurology, Department of Neurobiology, Duke University School of Medicine; Department of Psychology & Neuroscience, Trinity College of Arts & Sciences; Director of Education, Duke Institute for Brain Sciences; Duke University
Okay. Now, I think we're ready to apply this
embryological framework to understand the organization of the cranial nerve nuclei
in the brainstem. So this is a chart you might want to have
in front of you for a little while, so that you can begin to make sense of all of
this new anatomical information that I'm sharing with you in this tutorial.
So what this chart does is it organizes the brainstem according to embryological
division, that is midbrain, pons, and medulla.
And also, organizes across are various ways of breaking down motor outflow and
sensation according to our embryological framework.
So we have six columns in this chart. We have three to the left of center for
motor control and three to the right for sensation.
And for motor control, we recognize a somatic motor division, a branchial motor
division, and a visceral motor division. So here is how I want you to think about
this. I want you to think about each
embryological division of interest for motor control and for sensation, and
consider what's in the midbrain, what's in the pons, what's in the medulla?
So, for example, let's think about the motor control for the muscles that are in
the cranial region that are derived from cell mites.
And it's fairly simple. It's the muscles that move the eyes in the
orbit and the muscles that move the tongue.
So the muscles that move the eyes are related to cranial nerves III, IV, and VI.
Cranial nerves [inaudible] and IV are found in the midbrain.
Cranial nerve VI attaches to the junction of the pons and the medulla, but the
nucleus that grew out those axons is found in the caudal pons.
The axons that move the tongue are derived from the hypoglossal nucleus, which is
found in the rostral part of the medulla, so we have a hypoglossal nucleus.
So one way to approach this challenge is to consider how the outside of the
brainstem is related to what we find on the inside.
So, again, taking our somatic motor nuclei as an example, we have the nerves that
move the eyes, the oculomotor nerve, trochlear nerve, and the abducens nerve.
Two nerves associated with the midbrain. One associated with the caudal pons.
Up here in the midbrain, we have our oculomotor nucleus growing out these axons
to move the eyes. The trochlear nucleus growing out the
axons in the fourth nerve. And the abducens nucleus, growing out the
axons in the abducens nerve. Now the muscles derived from the
pharyngeal arches we call those branchiomeres or branchiomeric muscles and
the motor nuclei that innervate those muscles are called the branchial motor
nuclei. And, we just think about what are they.
Well, they are the muscles of mastication, that is the muscles involved with chewing.
They are innervated by a motor component of the trigeminal nerve.
There's the muscles of facial expression that are innervated by the facial nerve.
So, these axons are grown out by the facial motor nucleus so both the
trigeminal motor nucleus and facial motor nucleus are going to be found in the pons.
Now, a little less obvious, but important nevertheless, are the muscles that are
deep within our neck region, around our larynx and our pharynx.
Those muscles are controlled by components of cranial nerves IX and X.
The glossopharyngeal nerve and the vagus nerve.
And the axons that are governing these muscles deep in the larynx and the pharynx
are grown from neurons in what's called the nucleus ambiguus for reasons that I
think will be obvious to you shortly. And then finally, we have our spinal
accessory nerve. The spinal accessory nerve innervates also
muscles derive from the pharyngeal arches that are involved in turning the head and
shrugging the shoulders. That would be the sternocleidomastoid
muscle and part of the trapezius muscle. Now, let's move on, and think about our
visceromotor elements. So, within, within our eyes, we have a
smooth muscle in the iris that constricts the pupil.
And that constrictor function is derived from parasympathetic neurons that send
their axons out through the oculomotor nerve.
And these parasympathetic preganglionic axons live in a small nucleus that sits
right on top of the oculomotor complex. That nucleus is called the
Edinger-Westphal nucleus. So that is our most superior visceral
motor nucleus in the brainstem. Deep in the pons, and we won't see them
here in this view from the outside, are the nuclei that are responsible for the
secretion of saliva and also the secretion of tears from the lacrimal gland.
So we have these salivatory nuclei that sit deep in the pons and they send axons
out through cranial nerves VII and IX to their respective targets in the orbits,
and in the, oral pharynx. Also in the junctional region near the
pons and the medulla, we have the neurons that are associated with cranial nerve X.
The vagus nerve that control the visceral that are found in the thorax and the
upper, upper part of the abdomen. So these axons are grown out by the
nucleus ambiguus and by the dorsal motor nucleus of vagus.
Now notice that we've named the nucleus ambiguus twice, and I don't want you to be
confused about why that is the case. There is some historical reason why we
call two different sets of neurons that convey two different modalities and motor
control part of the same nucleus. But they are not the same cells that
supply the pharynx, larynx on the one canned for the branchial motor control.
And the cardioinhibitory output that slows the heart via the vagus nerve on the
visceral motor side. So, two different populations of neurons
that sit within the same nuclear complex of the upper part of the medulla.
Moving on now to the sensory side, we have our general sensory signals that are
coming from the skin surfaces of our face and our head and some of the deeper
structures associated with the muscles of our face.
These are giving rise to signals about, like touch, about movement, about pain,
and temperature sensitivity and all of this information is conveyed to the
central nervous system across four cranial nerves, cranial nerves V, VII, IX, and X.
And all this information is fed into that long trigeminal nuclear complex.
And if I look again at the brainstem model, we see a long nucleus that seems to
just snake its way down from the midbrain or the mesencephalon through the pons and
into the medulla. That's our trigeminal nuclear complex.
And so the mesencephalic portion of it, that is the midbrain portion of this, this
is where we find our movement-sensitive somatic sensory signals related to the
movements of muscles in our face, especially the movements or our chewing
muscles and the movements of the temporal mandibular joint.
The sensory signals that are derived from our skin surfaces pertaining to light
touch and other aspects of mechanical sensation are fed into what's called the
principal nucleus of the trigeminal, which is that large, bulbous structure in the
pons. And these signals are derived mainly from
the trigeminal nerve, but also a small contribution related to a little patch of
skin in the external ear that's conveyed across cranial nerves VII, IX, and X.
And then lastly, we have the spinal trigeminal nucleus.
And this is the inferior or caudal extension of this nucleus that receives
pain and temperature information. We'll talk much more about both of these
two preceding divisions of the trigeminal system as we get into a discussion of
mechanosensation and pain and temperature sensitivity.
Okay. Well, this leads us then, with a brief
consideration of our special sensory systems, and then, our visceral sensory
systems to our special sensory systems that are connected to the brainstem.
Are those related to our sense of hearing or auditory system and our sense of
balance being derived from the vestibular system deep within the petrous temporal
bone. So both of these two special sensory
systems are sending signals to the brainstems via the eighth cranial nerve.
And those signals, diverge once they enter the brainstem into different sets of
nuclei. There's a set of nuclei related to
hearing, called the cochlear nuclei, and then, a set of nuclei related to our sense
of balance, equilibrium. Basically, the accelerations of our head
and the static positions of our head. That's the vestibular nuclear complex of
the brainstem. Both of these nuclei are found near the
junction of the pons and medulla. And finally, we have our visceral sensory
signals that enter the brainstem via cranial nerves VII, IX, and X.
We can divide them into special visceral sensory, meaning, basically our sense of
taste, and that sense innervates the rostral part of this nucleus of the
solitary tract. The other aspect of visceral sensation is
more of a general sense of visceral sensation that is conveyed to the same
nucleus, but to a caudal division of it. So the nucleus of the solitary tract is
all about visceral sensation. I'll just put this table in front of you
again which runs through the cranial nerves and gives you a sense of where the
nuclei are to be found. And what they are as they relate to these
cranial nerves and also says a word about how one might think about testing the
function of these, these nerves. So you might want to take a moment at some
other point, come back to this table and maybe try to do some of these tests on a
friend or a family member. They're pretty easy to do, they don't
really require any special equipment and if you just think about the actions of our
muscle systems and the activities of our sensory systems, I think you can very
readily figure out how a clinician might go about testing the integrity of the
function of each of these cranial nerves. And, if you want to see how a clinician
might do this, I would refer you to an excellent website that is, maintained by a
fantastic neurologist and author, Dr. Hal Blumenfeld.
That website is neuroexam.com, so check it out.
You'll see lots of cranial nerves, being tested and the standard way the
neurologist would do it, so, I would encourage you to have a look at that,
neuroexam.com. Okay.
Finally, we are ready to actually look at into the brainstem and find these cranial
nerve nuclei. So, we can do that by looking at some
cross sections and the figure in front of you here shows cross sections through
various levels of the brainstem, beginning at the top of the brainstem with the mid
brain. So, in a section through the midbrain, we
should be thinking about, okay, what are the nerves that connect to the midbrain
again? Remember, nerve III, nerve IV.
So nerve [inaudible] is in a more superior position.
And that's what we find in this first slice.
We find the oculomotor nucleus and the Edinger-Westphal nucleus, both growing
axons out to the third nerve. Now, not illustrated here because we'd
have to be right at this level, would be a view of the truncular motor nucleus, but
we'll see that in a few minutes. Now, below into the pons, at two different
levels of the pons we first find the principle trigeminal nucleus.
And the trigeminal motor nucleus sitting right next to one another at the level at
which the trigeminal nerve, actually, sends its axons into the brainstem.
So that's the level at which we have this slice number two.
Slice number three is just below it, and the purpose of catching this slice is to
show you the facial motor nucleus, which as a brachial merric motor nucleus, it is
just a little bit off of the dorsal aspect of the tegmentum.
Because of the anterior or ventral migration of these motor neurons in
development. So that's where we find our facial motor
nucleus. We also have some nuclei associated with
sensation here, the spinal division of the trigeminal nucleus.
In red here, we have the somatic motor nucleus, the abducens nucleus.
And then lastly, the vestibular nuclei that we're beginning to see as we get into
the caudal part of the pons. Now, we go just a little bit further down
near the junction of the pons and the medulla.
We find additional vestibular nuclei in about the same position, but we also see
the cochlear nuclei, which seem to sort of cap the dorsal lateral aspect of the upper
medulla. We're continuing to progress through the
caudal medulla. So we would expect to see the spinal
nucleus of the trigeminal complex, which we have here in this blue shape.
It's extending all the way down through the medulla, and in fact, will seem to
merge with the upper part of the spinal cord as the spinal nucleus of the
trigeminal complex merges with the dorsal form of the spinal cord.
Well, there are a number of other nuclei to note here in the tegmentum of the
medulla, all in that dorsal region. And again as we, as we look at this, I
want you to recognize that the embryological framework helps us to
interpret this. So right along the dorsal midline, we're
going to expect to find a somatic motor nucleus, that's were we find the
hypoglossal nucleus. Now just to the lateral side of that
somatic motor nucleus. We might expect to find a visceral motor
nucleus and we do. We find the dorsal motor nucleus of vagus.
Alright, now just lateral to our motor nuclei, we should expect to get into
sensory nuclei. And indeed we do.
First we find the nucleus of the solitary tract, which is found right there in
purple shade and just lateral to it we find our special sensory nuclei, the
vestibular nuclei. So, again, motor nuclei are medial,
sensory nuclei are lateral. And then, finally, in the far lateral
region, that's where we find our trigeminal system.
Okay, and finally down in to the section number six that we see here in this
illustration, we have the caudal part of the medulla getting close to merge with
the upper part of the spinal cord. And we essentially see the same set of
cranial nerve nuclei just in a slightly different positions.
And some are reduced in size, with the exception of the spinal trigerminal
nucleus that continues to be a prominent feature of the medulla throughout its
entire link. Okay, so, what I like to do with you next
is to get into Sylvius and show you what these nuclei actually look like in
histological sections taken through the brainstem.
So, if you're ready for a break, this would be a good time to pause and open up
Sylvius and, get ready to, perhaps, go back and forth between the remaining
segment of this tutorial. And Sylvius, should you have it.
If you don't have Sylvius, that's fine. Just refer back to my tutorial notes, as
well these images, and this movie file, and follow along as I give you a tour of
the brainstem through our histological atlas that we have in Sylvius.
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