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.
Emotional Motor System
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Medical Neuroscience
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From the lesson
Movement and Motor Control: Lower and Upper Motor Neurons
We come now to another pivot in Medical Neuroscience where our focus shifts from sensation to action. Or to borrow a phrase made famous by C.S. Sherrington more than a century ago (the title of his classic text), we will now consider the “integrative action of the nervous system”. We will do so in this module by learning the basic mechanisms by which neural circuits in the brain and spinal cord motivate bodily movement.
Meet the Instructors
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. we now come to part four of our
discussion of upper motor neuronal systems for motor control.
And we come to a topic that has always intrigued me.
And I've always found it very very much fun to explore and to, to talk about.
it's a discussion of what might be considered to be an emotional motor
system. So my learning objective for you is to
simply discuss the evidence that there actually exists an emotional motor system
within our bodies' systems for governing movement.
Well, I'm going to suggest again to you that one principle theme for motor
control is that there are parallel pathways by which upper motor neurons can
govern the activities of lower motor neurons.
Now we've spent a good bit of our time so far, talking about what is depicted here
on the left-hand side of this figure. That is a set of pathways that come from
upper motor neurons in the motor cortex and in the brain stem that are concerned
with the expression of skilled behavior. And this would involve the lateral
pathways that come from the motor cortex to the lateral part of the ventral horn,
being concerned with the fine control of the distal extremities.
And then in order to facilitate the expression of skill, there are pathways
that come from the brain stem, primarily. That are concerned with adjusting posture
and setting the stage for the expression of that skill.
This involves making adjustments to the gain of our segmental reflexes.
And so these brain stem systems send projections to lower motor neurons.
there's in particular, a role for the reticular formation of the brain stem.
In adjusting the gain of these pools of lower motor neurons.
Now, what I'd like to turn to is a concept that in parallel, there are
projections from other parts of the forebrain.
Other regions that give rise to connections.
Primarilly, to the reticular formation of the brain stem.
But perhaps also directly to pools of lower motor neurons in the brain stem and
the spinal chord. And, these regions of the forebrain that
I have in mind are not in the posterior frontal lobe.
So we don't conventionally consider them to be part of what is sometimes called
the pyramidal motor system. That is, the parts of the, of the
meta-cortex that give rise to the cortical spinal pathway that can be found
in the medullary pyramid. For this reason, we call these
extrapyramidal projections. And these extrapyramidal projections are
coming from limbic centers in the ventral and medial parts of the forebrain.
Including some structures in the medial part of the temporal lobe, such as the
amygdala, and parts of the ventral part of the forebrain, such as the
hypothalamus and the diencephalon. So these so called limbic centers then
give rise to projections that run in parallel to those that are emanating from
the posterior part of the frontal lobe. And the upper motor neurons of the brain
stem. So, these pathways are largely involved
in the expression of non volitional behavior.
That we associate with emotion. These pathways are also those that are
engaging our bodily systems, both our somatic motor systems and our visceral
motor systems for emergency situations that might require fight or flight.
In order to try to be somewhat consistent with our lateral and medial scheme that
we talked about for control of volitional movement.
We can likewise recognize a lateral and a medial scheme for the organization of
these parallel descending projections in this emotional motor system.
The lateral system is involved in expressing specific emotional behaviors
particular gestures of our facial region for example.
That communicate particular emotion or particular postures that are involved in
non verbal communication. These tend to run through pathways that
can be found in a more lateral region of the tegmentum of the brainstem.
There are more medial pathways that are concerned with setting the stage.
And these pathways are adjusting gain of reflexes.
Perhaps making it more or less likely that we might express a particular
emotional. Behavior in our facial muscles.
So, let me give you an example of this emotional motor system in action.
So, I'm going to use some now quite old pictures of my son who is now in his
adolescent years. But in his younger years, it was very
instructive for me to think about the operation of a pyramidal motor system for
volitional control. And the operation of an emotional motor
system which moved the muscles of the face and our posture in a way that
conveyed true emotional significance. Well let me show you a picture of my son
when he was about 18 months old. So typically when we would approach him
his name is Jonathan, and we would try to get him to smile, we'd say you know,
smile for the camera Jonathan, this is what we would get.
something that we sometimes call around here, a cheesy smile because sometimes
people say cheese in front of a camera to try to create sort of a false impression
of an actual emotional smile when in fact it is a volitional motor act.
And so this is what my son is doing here. So, we're trying to get him to smile and
you can see that he is constricting his orbicularis oculi.
He's trying to show his teeth here and so in his 18 month old mind he is doing what
we want him to do, he's expressing an emotion.
But, as parents we know well, this isn't really what we wanted to photograph, we
wanted to really capture him expressing a true emotion.
Well, if you knew my son, you'd know that he was a rather stoic young man and
seldom truly expressed his emotion. this was a different setting where we put
him up in a studio to get his picture taken, and the photographer is waving a
stuffed animal in from of him, trying to entertain him, get him to smile.
And so, so what we see here is about as close to a happy expression as we ever
saw in our 18-month old son. and and contrast that to this very forced
facial expression it's quite easy to tell the difference between which expression
came from a force of will, and which perhaps reflects a true experience of
emotion. So why do you think we're so good at
telling the difference between a genuine emotion in a smile and a forced smile?
Well, I think partly the answer is that we understand, whether we articulate in
these terms or not. That there are different neural centers
in the fore-brain that are organizing the expressions in the human face that are
conveying genuine emotion or a contrived volitional motor act.
That is meant to imitate that emotion. Well the genuine emotion that we might
experience and express in the muscles of our face is motivated primarily by the
medial divisions of the premotor cortex that run into the banks of the singular
[INAUDIBLE].
In fact, there's a region. Right in about this region of the human
brain called the cingulate motor area. And this region is active when we express
an emotional smile. However, if we present a cheesy smile, a
pyramidal smile to a camera, that smile is being organized and executed.
By motor circuits in the lateral and inferior part of the premotor and primary
motor cortex. This is a pathway that runs along the
corticobulbar path in parallel with the corticospinal fibers, so we consider this
to be part of our pyramidal motor system. So quite different regions of the
forebrain are responsible for the emotional smile, and what we sometimes
call the parabital smile. Now, if you view the tutorial that I've
prepared to discuss the control of facial expression by upper motor neurons.
You'll realize that there's also and important clincal side, that can be
associated with the connection between these two different parts of the
pre-motor cortex and the lower motor circuits of the facial motor nucleus.
So so please take some time and review that tutorial because testing of facial
motor. Performance is a key part of the
neurological exam. I'd like to give you one more example of
how our volitional motor systems and our emotional motor systems are integrated
and coordinated to produce a desired motor output in this case the example is
human speech. Now, my speech isn't particularly
emotional at the moment. I suppose it could be but, you sort of,
know what you're getting from me at this point in the course.
but nevertheless, we can break down speech into different components, right?
So there is the pure active vocalization That is, just producing the sound itself.
So that requires some coordination, of motor output.
And then there is, of course, what we're interested in and that is the semantic
content of speech. That comes with the production of the
phonemes that are representing the vowels, and syllables, and the structure
of the vocalization that conveys the semantic content.
So it's necessary to integrate these two components of speech in order to actually
produce understandable human language. So how does this happen?
So these different aspects of speech are coordinated by motor output from the
brain stem. So, for example one needs to coordinate
the movements of the mouth mouth opening contractions of the floor of the mouth
the movements of the tongue movements of the pharynx and the larynx in order to.
Coordinate that vocal motor apparatus for the production of the speech sounds that
are necessary for intelligible language, but there's also coordination of
respiratory rhythms and the muscles that force air through the larynx.
So there's additional musculature that must be coordinated with the vocal motor
apparatus found in the oral pharynx and larynx.
And so this all occurs through the activity of lower motor circuits.
These lower motor circuits involve the nucleus ambiguous, the facial nucleus.
The trigeminal motor nucleus, the hypoglossal nucleus and the dorsal motor
nucleus of vagus. So already, you can understand the
complexity of motor output that is required to make human speech.
Well, when we back up now and consider how do upper motor neurons govern these
lower motor neurons we learn a little bit about the organization of parallel
pathways. So, concerning the semantic content of
speech this information is processed in our lateral pre-motor cortex.
In that very special part that we call Broca's area, that is especially
concerned with expressing human speech. Well Broca's area, being part of our
premotor cortex, sends projections to these lower motor neurons.
And also sends connections to our primary motor cortex that interact with these
lower motor circuits and this helps give some structure to the vocal articulation
of speech. But these signals would not be sufficient
in and of themselves to produce speech. In addition to those projections that are
emanating from the lateral part of the pre-motor cortex, we also need to engage
our medial pre-motor regions, as well as structures including the amygdala.
And the hypothalamus that are going to be important for[UNKNOWN] speech with
emotion. And so there relays from these ventral
and medial regions of the fore brain to the structures in the brain stem.
Including cell groups that are part of this periaqueductal grey region of the
mid brain and in turn the periaqueductal gray sends connections to the reticular
formation. Especially parts of the medullary
reticular formation, that then interact with our lower motor circuits.
So the coordination of, of these two limbs is what is necessary to produce
human speech, so of course, ultimately that coordination is derived from
executive centers in the prefrontal cortex.
Well, I think speech is perhaps a surprising example of convergence of
parallel motor commands from very different parts of the brain.
That are responsible for creating the complete expression of human speech.
That has semantic content. We can think of that as a skilled
articulation of our vocal motor apparatus, but also has the necessary
gain. That has the necessary tone, and has.
structure that we interpret as emotion. And these signals are modulated by very
different parts of the pre motor cortex, and even regions of the brain that are
outside of our conventional collection of centers that we call the motor system.
I'm thinking now of the hypothalamus and the amygdala.
That contribute to the expression of emotion in human speech.
Okay, we've finally come to the final part of this rather lengthy tutorial on
upper motor neurons. And what I'd like to talk about next in
our final segment is the clinical picture that we would discover in an individual
who has suffered injury or disease that affected upper motor neurons.
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