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.
Cerebellar Circuits, part 1
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Medical Neuroscience
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从本节课中
Movement and Motor Control: Modulation of Movement
Next, we will consider two major brain systems that modulate the output of upper motor neuronal circuits: the basal ganglia and the cerebellum. Take note: the output of these systems is NOT directed at lower motor circuits directly; rather, their output engages the motor thalamus and brainstem upper motor neuronal circuits. Thus, the actions of the basal ganglia and cerebellum are to modulate, rather than command, the activities of upper motor neurons. As you study the lessons in this module, appreciate how the basal ganglia and cerebellum function in a somewhat complementary fashion to modulate the initiation and coordination of movement, respectively.
与讲师见面
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
Welcome back to our tutorial on the cerebellum.
And in this part, I'd like to take a closer look at the circuitry of the
cerebellum. And my learning objectives for you, are
that I want you to be able to make a sketch, of the major inputs and outputs
of the cerebellum. So, as all sketchers that I encourage you
to make, the bigger the better. As you're making your sketch, I want you
to be able to have a discussion. perhaps with a friend, a family member.
Maybe someone who's taking the course along with you.
But have a discussion. Even if it's just to hear the sound of
your own voice. I would encourage you to describe the
circuitry, that's involved in the processing that runs through the
cerebellum. And as I'd like to describe for you, we
can conceptualize this circuitry as involving a main excitatory loop that
runs through the deep nuclei of the cerebellum.
And then an inhibitory side loop, that runs up through the cortex and then back
down to the deep cerebella nuclei. Before output leaves the cerebellum to
influence circuits of upper motor neurons.
Well, before we talk in detail about those circuits.
I want to give you just a broad overview of the inputs to the cerebellum, and then
talk just a little bit about function. So, the main inputs for the cerebellum
come from a couple of different sources. they come from the pontine nuclei.
These would account for the majority of the inputs to the cerebellum..
And notice the relationship of the pons to the cerebellum.
The input from the pontine nuclei crosses the midline of the brain stem and
projects into the contralateral hemisphere of the cerebellum.
And the pathway by which it crosses the midline and enters the cerebellum, is the
middle cerebellar peduncle. Now, notice that these pontine nuclei are
in turn supplied by inputs that are derived from the cerebral cortex.
So, the cerebral cortex then has the means by which it can send signals into
the cerebellum, but only indirectly, through a replay in the pons.
And as we discussed in the opening to the first part of this tutorial, one
important function of the cerebellum, is to integrate executive commands about how
we intend to move our body. Well, this is how this happens.
Through input from the cortex to the pontine nuclei that are at the base of
the pons, there's a synaptic connection. And then a relay from the base of the
pons into the contralateral cerebellum. And notice that the input is being
distributed both to the cortex of the cerebellum as well as to its deep nuclei.
Well that's one massive and very important source of input to the
cerebellum. Another important source of input to the
cerebellum comes from our sensory systems, and specifically, from our
proprioceptive systems, concerning the movements of our arms and legs.
And this is fed into the cerebellum, via relays from the spinal cord in the caudal
part of the medulla. And then there are inputs concerning the
movements of our head. And these are conveyed into the
cerebellum via the vestibular nuclei of the dorsal lateral tegmentum of the upper
medulla and the caudal pons. And at least for some ganglion cells in
the vestibular division of the eighth nerve, there may be direct connections
from the eighth cranial nerve into the Cerebellum.
So the cerebellum is getting this very important sensory feedback about how
we're moving our bodies with respect to spinal cord inputs.
And then, how our head is moving through three dimensional space.
Well, there's a third major source of input to the cerebellum that I want to
mention. And it's coming from a really fascinating
nucleus of the ventral, and, somewhat intermediate aspect of the medulla.
It's called the inferior olive, or the inferior olivary nucleus.
This nucleus sends axons across the midline, then into the cerebellum from
below, via the inferior cerebella peduncle.
And the inferior olive is providing a learning signal for the cerebellum, and
we're, we'll, we will talk about this in some detail.
But, essentially, what this signal is doing is, it's conveying to the
cerebellar cortex a time for synaptic change.
And this synaptic plasticity appears to be the cellular and synaptic basis for
motor learning in the cerebellum. Now, this inferior olive, in turn, is
getting inputs that are descending from a pathway derived from the cerebral cortex.
And the relay in this pathway is the red nucleus.
So notice that the cortex is sending it's executive signals into the cerebellum via
relay in the pons. But it's also informing the red nucleus,
which is in turn activating the inferior olive.
And when the inferior olive is active, now the cerebellum will engage in
synaptic plasticity. And we think produce an error correction
signal that can improve performance. Now, let me say just a few more words
about the organization of these inputs, before we look at a more fine grain level
at the organization of the circuits in the cerebellum.
So, we have some anatomical terms that I want to define for you.
they reflect the names the anatomists have given to the appearance of the
inputs that we see under the microscope when we look at the cerebellum, at the
cortex and at the deep nuclei. What we see when we look at the inputs
that are coming from the pons, and those that are coming from the spinal cord and
the vestibular nuclei. What we see is a morphological appearance
of the input that we call the mossy fibers.
So these inputs give rise to what we call mossy fibers, and this is now a bit of a
shorthand term to describe all of this afferent input that is converging on the
circuitry of the cerebellum. All except for one, very special kind of
input, and that is the input that's coming from the inferior olive.
This one type of input we call the climing fiber, and the reason we call it
the climbing fiber should be obvious in just a few minutes.
It has to do with the intimate relationship of the axons of this
inferior olivary neuron, with respect to the principle cell type that we find in
the cortex of the cerebellum. Now let me emphasize that both the mossy
fibers and the climbing fibers, terminate at both levels of cerebellar processing,
in the cerebellar cortex, and also in the deep nuclei.
Now perhaps, it will be helpful just to remind you a bit of the inputs, to the
cerebellum with a little bit more detail. you will recall that the inputs to the
cerebellum from the spinal cord, convey signals about the movements of our body
that are sensed by our preparative receptors.
And they are conveyed the pathways that serve the lower extremities and the upper
extremities. The pathway that serves the lower
extremity involves a relay in the dorsal nucleus of Clarke, which is found in the
thoracic segments of the spinal cord. The dorsal nucleus of Clarke grows an
axon, that runs up the dorsal lateral white matter of the spinal cord and forms
a tract that we call the dorsal spinal cerebellar tract.
This is the major relay of proprioceptive signals from the lower extremities into
the cerebellum. This pathway runs on the ipsilateral side
of the cerebellum and the spinal cord. So the cerebellum is getting information
about the movements of the ipsilateral side of the body.
the same is true for the upper extremity, and this pathway runs from the first
order neuron in the spinal nerves that enter the dorsal column.
And then there's a synapse in the external cuneate nucleus the most lateral
of our dorsal column nuclei. And from there the second order neuron
projects, into the cerebellum via the inferior cerebellar peduncle in parallel
with that dorsal-spinal cerebellar tract. And the cuneocerebellar tract is now
involved with conveying proprioceptive signals about the movements of the upper
extremities, into the cerebellum. So that's what we find here in the input
from the spinal cord. So this input from the spinal cord is
going be directed again, mainly at that, median zone of the cerebellum that we
call the spinal cerebellum. The cerebral cerebellum on the other
hand, is going to get information that is principally relayed via these pontine
nuclei. So this massive connection from cortex to
pontine nuclei to cerebellum is mainly going into the lateral hemispheres, into
that region that we call the cerebral cerebellum.
And then these vestibular inputs, that are being sent in some cases directly
from the eighth nerve into the cerebellum.
And others in a relay through the vestibular nuclei of the brain stem.
these are being conveyed to the vestibular cerebellum, that
flocculonodular lobe that's tucked underneath the posterior part of the
cerebellum. One final point to make about the
organization of the circuitry that should have been evident to you as we've been
talking about it. And that is that the cerebellum is
representing the ipsilateral side of the body.
So perhaps I'm belaboring this point just a bit, but it certainly is worth some
added emphasis. perhaps the spinal cord is what first
sets up this ipsilateral representation by virtue of it's Ipsilateral dorsal
spinal cerebellar pathway, that runs in via the inferior cerebellar peduncle.
But, this principle of ipsilateral presentation in the cerebellum creates a
bit of a problem, does it not? Because you now understand, that when it
comes to the cerebral hemispheres, the principle is contralateral
representation. So this means that, one side of the body
is going to be represented in the opposite cerebral hemisphere, but in the
same sided cerebellar hemisphere. And perhaps this provides a helpful way
to just think through the necessity of this connection from cortex to pons, and
then from pons to cerebellum. This will also be a challenge when think
about the outputs of the cerebellum. That provide a means by which the
cerebellar hemisphere on one side of the midline, can relate to circuits of upper
motor neurons on the opposite side. So we'll face that challenge when we see
an analogous figure that will be illustrating the output pathways of the
cerebellum. But with respect to input, we can see how
the spinal cord seems to set up this ipsilateral representation.
And then the relay from the cortex meets the appropriate constraints, allowing one
side of the cerebrum to interact with the appropriate hemisphere of the
cerebellum.
