The basal ganglia – The direct pathway | Nervous system diseases | NCLEX-RN | Khan Academy

The basal ganglia – The direct pathway | Nervous system diseases | NCLEX-RN | Khan Academy


– [Voiceover] Every day we
make hundreds of movements, from reaching for our first
cup of coffee in the morning to waving hello or good-bye
to someone that we know to using utensils to eat our food. And we actually have this
really incredible system in our brains that allows
us to make these movements, and it prevents unwanted
movements from happening, and it does this in this
really smooth, streamlined way that we don’t even really notice. So this system is called
the basal ganglia, and the basal ganglia is
actually a collection of nuclei, and here when we say
nuclei what we mean are structures that are just kind of made up of a bunch of neurons. So these little clusters of neurons. So the basal ganglia is made up of a few of these clusters
of neurons, these nuclei, and before we actually go through how they together control our movements, let’s just first have a look at where these structures are in the brain. So here we have a diagram of the brain, and the way that we’re looking at it is as though we sliced it, and we kind of split up the front and
the back of the brain, and now we’re looking inside
one of these sections. And we call this a coronal section. So if we look here, this is the putamen, and over here is the body
of the caudate nucleus. And down here we can actually see the tail of the caudate nucleus, and the putamen and the caudate nucleus together actually form
what we call the striatum. And if we look back over here, we can see what we call
the globus pallidus, and this is the external part, the external globus pallidus, and this is the internal part. And if we look down here
at this black structure that we have on our diagram, this is the substantia
nigra, and we call it this, we call it the substantia nigra, which means black substance,
because the neurons here they have this pigment
in them, this coloring, that makes them actually
look black in the brain. And we can actually see this darkness of the substantia nigra quite
nicely if we look at an MRI. So in this MRI of the brain, you can see these little black areas here
on both sides of the brain, and this is the substantia nigra. And if we head back over to
our diagram of the brain, we have over here the subthalamic nucleus, and we call it this because
it actually sits below, sub meaning below, the thalamus. So except for the thalamus,
these are the components of the basal ganglia that
we need to know about to talk about movement. So all of these structures,
including the thalamus, they work together to
control our movements, and the way that they do that, the way that they
communicate with each other, is through these pathways. And we’re going to talk
about these pathways, but this communication in these pathways is controlled by neurons,
neurons talking to each other. So before we dive into these
details of these pathways, I’m going to throw some
terminology at you, just so that things make
a little bit more sense as we’re going along. So when a neuron goes from one
part of the brain to another, it actually communicates
with another neuron at its destination, and it does this at what we call a synapse. And it’s here that the first neuron, which we call the presynaptic neuron, that came from the first location, and the postsynaptic neuron, which is in the arriving destination, this is where they talk, and
they talk by sending chemicals that we call neurotransmitters. So the presynaptic neuron
sends a bunch of chemicals to the postsynaptic neuron, and depending on what kind
of chemicals they send, the postsynaptic neuron may have different things happen to it. So one important neurotransmitter that the presynaptic
neuron can send is GABA, and GABA we call our main
inhibitory neurotransmitter, and we call it this, this
inhibitory neurotransmitter, because it has this inhibitory effect on the postsynaptic neuron. So it kind of turns it off. It turns its activity off. It inhibits it. So another neurotransmitter that the presynaptic neuron could send is one that excites the second neuron, excites the postsynaptic neuron and turns its activity up. And the main excitatory neurotransmitter is called glutamate, and
this increases activity in the postsynaptic
neuron when we excite it. So all of this will become important as we go through these pathways. So there are two big things
that we need help with, when it comes to movements. The first is that we actually
need help making a movement. So we need help getting
from saying to our bodies, hey, I want to move my arm, I want to grab that cup of coffee, to the point where we
actually are moving our arm. So everything in between
we need help with. And the second thing we need
help with is not moving, making sure our muscles are
not moving when we’re at rest or when we just don’t want them to. So the pathway that takes
care of this first one here, we call the direct pathway, and the pathway that takes
care of the second one here, we call the indirect pathway, and both of these pathways, we call these the pathways of the basal ganglia. So they’re involving those structures that we looked at before when we were looking at the brain. And we’re going to go
through the direct pathway. So these are the
components of our pathway, and before we begin, it’s
important that we recognize that the thalamus here, the thalamus, it’s normally under
what we call inhibition. So this means that unless things change, the thalamus is, its
activity is being suppressed. It’s not allowed to be as
active as it wants to be. So the aim of the direct pathway is to take away its inhibition, to allow the thalamus to be more active, and that’s because the
thalamus is what talks to the motor cortex, which
then talks to our muscles, telling them to move. So if we want to get movement going, if we want to move our
arm, we need the thalamus to be able to be active. So that’s the aim of the direct pathway. So the first thing that
happens is up here, in the motor cortex,
and that’s when we say, hey, I want to move. So when we say that, an excitatory neuron from the motor cortex
goes to the striatum. So this is something that’s already there, but the motor cortex sends
an excitatory message to the striatum, and this
excitatory neuron here, it actually synapsis
with an inhibitory neuron in the striatum that’s heading to the globus pallidus internal. So when this exitatory message comes down this excitatory neuron and synapsis on this inhibitory neuron in the striatum, heading for the globus pallidus internal, what this does is it excites the striatum, and these inhibitory
neurons in the striatum, they become more active,
because the striatum is excited. So these inhibitory neurons,
they’re more active, and so they actually inhibit
the globus pallidus internal more than it would have
been before we sent this excitatory message
from the motor cortex. So this excitation that’s happening here is happening because of
glutamate being released, and this inhibition on the
globus pallidus internal is happening over here because
of GABA being released. So the globus pallidus
internal normally is what’s actually holding the thalamus down, keeping its activity down. So when its inhibited by
these striatal neurons, its activity is turned down. So when the activity of the
globus pallidus internal is turned down, it can’t
inhibit the thalamus as much as it normally would. So the thalamus is now
no longer as inhibited as it was, so it’s able
to get a bit more excited, a bit more active, and it’s
able to send excitatory messages to the motor cortex, because it has these excitatory neurons that go there. So it sends more and more
messages to the motor cortex, and the motor cortex gets more active, and it then sends excitatory messages to the muscles that we want to move. So that’s how we make those
movements that we want to make. So while all of this is going on, the substantia nigra and
the subthalamic nucleus, they’re actually kind of
working in the background to fine tune things. So the substantia nigra has these neurons that are dopamine neurons,
and they actually go from the substantia nigra to the striatum, where they synapse with
inhibitory neurons in the striatum that are going to the
globus pallidus internal. So kind of those ones that
we talked about before. So when the substantia
nigra is more active, it sends more and more dopamine to these inhibitory
neurons in the striatum that are heading for the
globus pallidus internal. And these inhibitory
neurons in the striatum, they have these dopamine receptors that we call D1 receptors. And when dopamine from
the substantia nigra binds to these D1 receptors on these inhibitory
neurons in the striatum, they get excited. And so, the dopamine coming
from the substantia nigra further excites these inhibitory neurons heading for the globus pallidus internal, and this results in even
more reduction in activity, even more inhibition of the
globus pallidus internal, and this allows the thalamus
to be even more active, because we’ve further blocked that signal. And back over here,
the subthalamic nucleus is actually what’s exciting
the substantia nigra. So it sends excitatory messages through excitatory neurons
from the subthalamic nucleus to the substantia nigra,
and this is what excites the substantia nigra and allows it to send more dopamine to the striatum. And the substantia nigra
can actually talk back to the subthalamic nucleus,
and it does this through inhibitory neurons, and
this allows it to say, hey, stop exciting me,
I’ve had enough excitement. So it actually inhibits
the subthalamic nucleus, which then stops the subthalamic nucleus from being able to excite
the substantia nigra. So when this happens,
when the substantia nigra isn’t being as excited by
the subthalamic nucleus, then it’s not adding to that
extra activity in the thalamus. It’s not allowing the
striatum to further inhibit the globus pallidus internal. And so, we don’t get as
much movement from muscles as we would if the
substantia nigra was excited. So together these structures
in the direct pathway, they work together to
ultimately increase excitation of the motor cortex, so
to make it more active and allow us to make
more muscle movements.


67 thoughts on “The basal ganglia – The direct pathway | Nervous system diseases | NCLEX-RN | Khan Academy

  1. I thought that striatum inhibits globus pallidus (ext), that inhibits globus pallidus (int), therefore the striatum activate the global pallidus (int). Can someone explain this to me? I'm very confused now.

  2. What is the name of the excitatory neurotransmitter that goes from the subthalamic nucleus to the substantia nigra?  Is it Glu or Dop or something different? Also coming back is it gaba?  It would be very helpful if you included all neurotransmitters in the future. : ) LOVE your work!  I don't know if you work in connectomics much regarding the 3 types of learning in real time….(physical structure of content, history of content and real time experience of content) I think your mother type voice regulates students making it easy to learn…lol….I know it sounds crazy but I think there is some truth to this.  I found it much easier to learn from your videos….I believe I already have circuits in place that recognize the soft tone of your voice….from -9 months to 8 years old my mom had a very gentle tone as I imagine most moms do.  Anyway, the point is when we are regulated it is much easier to learn. : )

  3. In this video you state that the "Thalamus" is always in inhibition. However, in your indirect pathways and your PD video. You state that the thalamus is always excited like a dog.

    So which is it? always in inhibition or excitation?

  4. Could you please tell me what is the program used in this clip? I have to make a clip for my senior project. Any recommended programs ? Thank you:)

  5. the best presentation i have ever seen concerning the basal ganglia. congratulations and thanks. YOU ARE THE BEST

  6. why can't lecturers at uni be like this pls? they made it sound so complicated and it is actually pretty straight forward. thank you <3

  7. thank you so much for this concise explanation! but could you please tell me, who order the subthalamic nuclei to excite at the 1st place? thanks!

  8. Great, simple, very informative. Only one question: what stimulates Subthalamic Nucleus to send an excitatory signal to Substantia Nigra?)

  9. took my professor 90 mins to explain this, and i was still confused came here watched once it now it all makes sense Eureka forrrealll

  10. it's said the striatum sends inhibitory signals to the globus pallidus but the globus pallidus is a part of the striatum, should be a little more specific there

  11. That u show there in coronal section Gp externus on right side is not that one….but rather is internal capsule….I think the marking is incorrect wrt gp externus

  12. It seems a little confusing that inhibitory signals from the globus pallidus internal to the thalamus cause excitatory signals from the thalamus. Especially since the same thing happens in the indirect pathway but leads to inhibition of the thalamus.

  13. So how do you explain tremors(which I presume is an increase in involuntary movement), in loss of Dopamine in Substantial nigra?

Leave a Reply

Your email address will not be published. Required fields are marked *