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.
Internal Anatomy of the Spinal Cord -Longitudinal Organization
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Medical Neuroscience
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Neuroanatomy: Internal Anatomy of the Human CNS
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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
Now, with some overview of the white matter and gray matter of the spinal cord,
I want us to turn to a very important consideration.
And that is understanding what we find at each level of the spinal cord.
And here's, I think, a very helpful figure.
What it does is it shows representative cross-sections that are taken from
different levels of the spinal cord. And I want you to notice a few features
that we find here. Essentially, what we find is that in the
region of the cervical spinal cord, and also, in the lumbosacral enlargement
region, we see an expansion of the amount of gray matter that's present in the
ventral horn. I think that should make good sense to
you. This gray matter is providing motor output
to the arms, in the case of the cervical cord, and to the legs in the case of the
lumbosacral enlargement. So, more neurons, more local circuits
means more grey matter volume that's governing what we do with our appendages
on our arms and our legs. In the thoracic spinal cord, notice that
the amount of grey matter in the ventral horn is reduced, compared to what we find
in the cervical and in the lumbar and sacral levels.
Okay, so, look at how much gray matter we have in the ventral horn, that will help
you identify the section. I also want you to notice the amount of
white matter that we have here in the spinal cord.
Now, for the amount of white matter in the cord.
I think it should make a certain amount of sense that it would decrease as we move
from superior to inferior. And it's decreasing for 2 reasons.
One reason is that the axons that are coming down from the brainstem and
cerebral cortex and the lateral and anterior column of white matter are simply
terminating along the way. So, if we looked at the upper levels of
the spinal cord we would expect to find more axons than if we were to look at the
lower levels of the spinal cord. Now, for a similar reason, our ascending
pathways that are sending signals, let's say about pain and temperature or
mechanosensation, up through the spinal cord are collecting at various levels.
And as a consequence, in the superior segments of the spinal cord we have more
axons conveying ascending sensory signals than we have at more inferior levels.
Now, if we then look at the cross sections of the spinal cord, I think it should be
obvious to you that we have a whole lot more white matter here in the cervical
cord compared to the very bottom of the spinal cord in the sacral region.
So, look for the amount of white matter that we find.
And we see that there is more white matter at the upper levels than in the lower
levels. Now, one key difference that I want you to
look for is the lateral margins of the grey matter of the spinal cord.
You'll note that in the thoracic cord there is a lateral protrusion from the
gray matter right near the junction of the ventral horn and the dorsal horn.
This is a feature that we call the lateral horn.
And this is a distinctive feature of the thoracic spinal cord.
And as we'll see, what's in that lateral horn are preganglionic sympathetic
neurons, that are providing outflow from the nervous system to the viscera.
We see a similar group of cells in the sacral cord, but they tend not to form a
pointy protrusion into the white matter. And at that level we don't call that a
lateral horn, but we do recognize another collection of preganglionic visceral motor
neurons, only in the sacral cord they're parasympathetic, whereas in the thoracic
cord they're sympathetic. All right.
Another key distinction that we need to make when we look at the spinal cord is in
the region of the dorsal column. So, remember the dorsal column is what we
find out here with dorsal being shown to the top of the image and ventral or
anterior to the bottom. What I want you to notice is that in the
dorsal column, there is more white matter in the cervical region, compared to the
lumbosacral enlargement for reasons that I just illustrated for you.
But I also want you to note that in the cervical cord, there is a distinction
between a lateral component of this white matter, and a medial component.
And as we talk about our pathways for mechanosensation, what you'll discover is
that the medial component is what we find at lower levels of the spinal chord.
But as we get into the region of the cervical enlargement, we begin to add
white matter from the sensory inputs that are attached to that cervical enlargement,
serving the upper extremities. While that wet matter begins to add up in
the lateral aspect of this dorsal column and the upper thoracic cord.
And then, we really see it adding up as we move through the cervical enlargement.
So, look for those divisions of the dorsal column when we look at cross sections
through the spinal cord. And we'll, we'll give these divisions
names. I don't need to tell them to you now but,
but just note that in the cervical cord the dorsal column is subdivided, whereas
in the lumbar and sacral levels, there's no such subdivision of the dorsal column.
Okay, now, I think we're ready to name some of these details.
And give you a chart that will allow you to explore on your own, cross sections
through the human spinal cord. So, this is a chart that lays out for you
some important internal features, in terms of grey matter and white matter.
And for white matter, I'm giving you the names of some of these important tracks or
pathways, that we will talk about in detail when we talk about mechanosensation
and our systems for pain and temperature. Well, let me orient you to this chart.
We have a list of internal features of the spinal cord in columns.
And then, our spinal cord segments organized according to cervical, thoracic,
lumbar, sacral and the one coccygeal segment.
And what I've provided for you is a check mark to indicate that, that grey matter
structure is present. So, as you've just seen, in an array of
cross sections, the Dorsal horn is present in each level of the spinal cord, as is
the Ventral horn. Okay?
So, we have a check mark for each of these longitudinal divisions of the spinal cord.
The lateral horn is that special feature indicative of the preganglionic
sympathetic neurons. And that's only found in the thoracic
cord. So, please note that.
The lateral horn is a feature of the thoracic cord.
Now, the rest of this chart pertains to white matter.
So, just with respect to the overall abundance of white matter, as I've
suggested, there is less and less white matter as we perceive from superior to
inferior. And with respect to the individual
pathways or the individual tracks of white matter that will be important for
mechanosensation and pain and temperature sensitivity, as well as for motor control.
We also see a general superior to inferior progression from more white matter
superior, to less white matter on the inferior side.
So these terms here Gracile tract and Cuneate tract, these are the pathways that
we find in the dorsal column. The Gracile tract pertains to the lower
extremity, the Cuneate to the upper extremity.
So, the Gracile tract begins to build up and its complement as we pass through the
portion of the spinal cord that receives input from the lower extremities.
We don't have a Cuneate tract until we get into the upper part of the thoracic cord.
And then, once we do, we rapidly add axons that are adding somatic sensory signals to
that dorsal column. Now, I'm going to jump to the far right
column, because this also is a somatic sensory pathway.
This pathway called the Antero-lateral system is found, as it's name suggest in
the anterior and lateral white matter of the spinal cord.
And this is the system that is conveying pain and temperature signals from the body
up into the brainstem into the forebrain. So, here we have a progressive addition of
white matter, as we go from inferior to superior levels.
Now, I'm talking about an ascending sensory pathway which is why my arrow is
going up. Now, finally, we have 2 pathways that
pertain to motor control identified here. A Lateral corticospinal tract which is
really the major motor control pathway that I will emphasize for you in this
course. But there's also a smaller, minor ventral
corticospinal tract. The major pathway, the Lateral
corticospinal tract descends with a progressive termination of axons as we go
from the upper part of the cord to the lower part of the cord.
And really, much of this pathway is concerned with what we do with our arms
and our hands and to perhaps a lesser extent what we do with our legs and our
feet. This pathway is all about controlling
voluntary movements, which mainly involves our arms and our legs.
So, there's not as denser projection to the Thoracic cord, but we still see the
pathways that are working their way down to the lumbar segment.
And then, once we get below the lumbosacral enlargement, this pathway
really drops out of the spinal cord. Now, this minor pathway, the Ventral
corticospinal tract, it's, a relatively small contribution.
And the axons tend to project along the length of the spinal cord.
Perhaps with some bias towards the lumbar levels.
Alright, well, now that we've had a broad conceptual overview of the spinal cord,
it's time to actually look at cross-sections and see these features
directly. So, I would ask that if you have Sylvius
Software, go ahead and open it and follow along with me.
If you don't have the software That's fine.
You can just continue to track with me as shift now to Sylvius and look through some
representative cross-sections of the spinal cord.
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