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Health and medicine
Course: Health and medicine > Unit 11
Lesson 2: Muscle innervationMotor neurons
How do neurons help us move? Learn about how motor neurons send signals to muscle cells and what happens when we damage this precious neurons. By Raja Narayan. . Created by Raja Narayan.
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Lol this was the funniest introductory attention grabber compared to all of the videos I've seen so far, props.
Are there any main differences between olioodendrocytes and schwann cells? Beside the fact that one is found in the CNS and the other in the PNS, respectively.(63 votes)
Oligodendrocytes main function is the insulation of the axons exclusively in the central nervous system of the higher vertebrates, a function performed by Schwann cells in the peripheral nervous system. A single oligodendrocyte can extend to up to 50 axons, wrapping around approximately 1 mm of each and forming the myelin sheath; Schwann cells, on the other hand, can only wrap around 1 axon.(27 votes)
at about6:40when you're talking about the empty space where the nodes of ranvier are located on the axon, is it correct to say that there is an empty space there?
iv'e learned that those expesed sections (nodes of ranvier) have a concentration of ion channels that are used to amplify the signal. also that the distance between node to node is spaced according to signals ability to travel and still be enough to cause depolarization to a threshold level of the next ion channel.
then again this also might be too much for the purpose and simplicity of this video?(12 votes)
I think you're right. The 'empty space' refers to the gap in mylenation, not a gap in ion channels.(11 votes)
Can Schwann cells be present in places other than the peripheral nervous system? He made it sound like they were ONLY present in the PNS. That doesn't make sense because cancer of the Schwann cells (called a Schwannoma) is most likely to occur in the 8th cranial nerve. Aren't the cranial nerves part of the central nervous system? If so, that would mean that Schwann cells are not only found in the PNS but in other places as well.(4 votes)- Schwann cells are normally exclusive to the PNS, but in some pathological situations they can invade the CNS (though this doesn't apply to the situation you brought up.) The cranial nerves are actually part of the PNS with the exception of the optic nerve, CN II, which is considered part of the brain. So Schwannoma of CN VIII would make sense because its part of the PNS, and thus has myelin consisting of schwann cells.(9 votes)
At approximately6:22Raja says of the signal going down the axon that when it comes to a myelin sheath, "it's going to jump". He draws the signal jumping outside the axon to the next place where there is no myelin sheath. The signal jumps over the myelin sheath?(5 votes)
Yes, the signal does 'jump' over the myelin sheath, as the sheath is made up of fat, making it an insulator providing electrical resistance. Since the Nodes of Ranvier (places that do not have myelin sheath), do not have any myelin (fat) surrounding it, the electrical signal may pass through it without having to 'jump'. The name of this process, where the signal jumps from node to node, is called Saltatory Conduction.(2 votes)
What are the differences between the oligodendrocytes and the schwann cell besides the oligodendrocyte being in the CNS and the schwann cell being in the PNS?(3 votes)
major difference between them is that oligodendrocytes provide covering around multiple axons (1 cell 'services' more axons) versus schwanncells which stick to just one axon. check the video's on neural celltypes in the "Nervous system and sensory information" section : https://www.khanacademy.org/science/health-and-medicine/nervous-system-and-sensory-infor(4 votes)
- is the upper motor neuron located in the brain stem while the lower motor neuron located in the spinal cord? Since one motor neuron has many terminal branches and since many of the muscle fibres is controlled by only one motor neuron to make a motor unit how long is the length of the axon of a motor neuron.(2 votes)
- An upper motor neuron, umn is in the brain or brain stem. A lower motor neuron, lmn, to the big toe has its cell body in the spinal cord and the axon has to go to the toe...So it depends on the person's height, but a meter long axon is possible. This information shows how peculiar and specialized these cells are and how impossible it is for them to repair well if injured. https://en.m.wikipedia.org/wiki/Upper_motor_neuron
https://www.khanacademy.org/science/health-and-medicine/human-anatomy-and-physiology/nervous-system-introduction/v/upper-motor-neurons(3 votes)
- Are lower motor neurons considered part of the PNS and upper motor neurons part of the CNS?(3 votes)
- Does the signal in axon 'jumps' or gets 'amplified' at nodes of Ranvier?(1 vote)
- I would suggest thinking of the action potential/ depolarization wave just "jumping" from node to node. The whole process is considered "saltatory conduction" which technically just means a jumping current. Remember that action potentials are an "All or nothing" kind of deal. There is no large action potential and small action potential so I wouldn't say the signal is amplified. Instead, the signal is allowed to travel over longer distances and technically faster because of the "jumping."(3 votes)
How does "nature plan for this"? Something more intelligent than chance has to have designed this function.(1 vote)- Nature does not "plan for" anything; species evolve based on selective pressures and random mutation. There is no "plan" for evolution, it is fundamentally driven by changes which increase an organism's chance of survival.
Obviously lifeforms evolved which needed to be able to conduct nervous impulses in a very efficient and fast manner in order to survive, thus the nervous system developed over time.
There is no evidence that there is any kind of 'intelligent design' behind the universe and to try and assert that there is is pure conjecture and fantasy.(3 votes)
- Are there specific places in the brain where the somatic nervous system is located?(1 vote)
- The somatic nervous system is part of the peripheral nervous system and therefor not in the brain (which is part of the CNS). It only receives input in the central nervous system (CNS), but rather makes up the peripheral motor neurons of the peripheral nervous system. There are regions of the brain associated with motor control, but they are part of the CNS.(3 votes)
6:40Video transcript
When we're at a dance
party, and we've determined that this is an
appropriate time to dougie, how does our brain
tell our body to do so? Well, in this video,
we're going to be talking about motor neurons. Motor neurons. These are the nerve cells
that come from our brain, go to our bodies, and tell
our muscles that it's time to contract . So let's start from the top. In the brain, we have what's
called an upper motor neuron. I'll just write "upper
motor neuron" right here. An upper motor neuron
sends a signal over to a lower motor
neuron, that I'll abbreviate right here--
lower motor neuron. And I promise I'm
going to draw this out in greater detail in a moment,
but just to kind of get an idea of what they do,
the lower motor neuron is the direct
messenger to muscle to tell it that it's time
to start contracting. The upper motor
neuron, because it's sending a signal to the lower
motor neuron, has two jobs. One, it'll also have the job
to tell muscle eventually that it's time to
start contracting. The other job it
has is that it has to tell lower motor neurons
when it's time to stop. It'll tell them that there's
no more signal coming in so you should stop telling
muscles to start contracting. So that's why upper motor
neurons have two functions. Let's take a look
at a lower motor neuron in better detail now. The first thing I like to
draw here is called the soma. The soma is just the body
of the lower motor neuron. The part of the
lower motor neuron that receives the signal
from the upper motor neuron is kind of branched like this. And there are
multiple projections that come off right here. These guys are called
dendrites, and they're going to receive the signal. It's where a signal is going
to dock on our motor neuron. And after it docks
the dendrite, passes through this station,
the soma, the cell body, it's cast away along an axon
that I'm drawing right here. And I've drawn this extra
long because there's going to be a lot going on
here before this slab of meat here, or muscle,
receives a message. So this is our muscle,
the motor end plate, or the muscle that's going
to receive information from our axon right here. So one more time, when
we're at a dance party and we decide that it's
time to shake a leg, how do we tell our leg
it's time to shake? Well, we have this
signal that's generated from the brain, travels
down the upper motor neuron, and then it goes to this
lower motor neuron right here. And the way I like to
think about a signal, it's kind of like how I think
about ships in the Navy. So if this little ship
right here is our signal, and it comes from our
upper motor neuron, it needs to have somewhere it
can dock on this lower motor neuron. That's what dendrites are for. This is where a signal
is going to dock. Once it docks there,
it has to pass through some type of station,
this naval station, which is what the soma is. And after it passes
through the station, it's going to move down the
axon where it's cast away. The axon is where a signal
is cast away from this motor neuron before it ends
up going to muscle. But what could happen here? What problem could
probably arise, considering how long
this axon actually is? Well, the signal could die off. It may not be able to make
it all the way to the end. And that's kind of what would
happen if you had a lower motor neuron injury or a lesion. If something were to happen
to our lower motor neuron, we wouldn't be able to
tell a muscle it's time to start contracting. Instead, you would have weakness
because your muscle would not be able to contract. The same thing happens when
you have an upper motor neuron injury. You're also going
to see weakness because you're not able to tell
the lower motor neuron it's time to tell the muscle it's
supposed to start contracting. But that's not the
key characteristic we see with upper
motor neuron injuries. The key thing we look
for is that we're not able to tell lower motor neurons
to stop what they're doing. And so because of that,
the lower motor neuron just keeps on telling this muscle,
hey, go ahead and contract. I'm not receiving any signal
from here to tell me to stop. And so because of
that, this muscle is just going to continuously,
spastically contract. And so a key symptom
or a key characteristic of an upper motor
neuron injury that you don't see with lower motor
neuron injuries is spasticity. And so that's what could
happen if you have dissipation of a signal at the
upper motor neuron. But nature has planned for this. What does she do to
make sure that we don't have our
signals dissipated? Well, she insulates our neurons. So I'm going to draw
three insulating cells right here that wrap the round
our axonal fiber right here, or this axon. And these three cells--
I'll label one right here. This is a single cell. It's known as a myelin sheath. That's an I. Myelin sheath. What does that mean? Well, myelin just means "fatty." So, yo mama's so myelin. They mean the same thing. Myelin sheath. And so we cover up the axon
fiber to help insulate it, so instead of a
signal dying off, it's able to go all the
way to the end over here. And depending on where you
have this myelin sheath cell in the body,
there's a different name. In our central nervous
system, which is strictly just the brain and spinal cord,
we call them oligodendrocytes. And that's only in the
brain and the spinal cord. In the peripheral
nervous system, which is literally everything
else, any other nerve in our body that's not in
the brain or the spinal cord, we call these myelin
sheath cells Schwann cells. So I've drawn three up here,
and what's going to happen is that you're not going to
have dissipation of your signal. No. Instead it's going to continue
on to this myelin cell and then jump and land
on this node right here, and it's going to jump again. And it keeps doing
this from node to node, or this empty space
to empty space, until it finally makes it
to the end of this axon, or what we call the axon
terminal right here. And so this space right
here, this open, empty area that has nothing in it,
has a specific name. We call this the
node of Ranvier, named after probably
the smartest scientist ever because he got his name
on a scientific structure that literally has nothing. This is just empty
space right here. And so as our signal is going
to propagate down this axon here and jump from node to
node, eventually it'll finally make it to
our axon terminal right here, where we can then
relay a message to our muscle that it's time to contract. And that's how our
motor neurons work.