Neurology | Basal Ganglia Anatomy & Function | Direct & Indirect Pathways

Summary

This educational video script delves into the anatomy and function of the basal ganglia, a group of structures in the brain vital for motor control. It outlines the components of the basal ganglia, discusses the direct and indirect pathways, and the nigrostriatal pathway, explaining their roles in initiating, modulating, and inhibiting movement. The script also highlights the clinical significance of these pathways in movement disorders like Parkinson's and Huntington's diseases, providing insights into the neurological basis of motor dysfunction.

Takeaways

• 🧠 The basal ganglia are a group of structures in the brain involved in motor control, consisting of the caudate nucleus, putamen, globus pallidus (internal and external), thalamus, subthalamic nuclei, and substantia nigra.
• 🔍 The striatum is a combined structure made up of the caudate nucleus and the putamen, which plays a significant role in the processing of motor information.
• 💡 The globus pallidus is divided into an internal and external part, with the internal part being a key component in the regulation of movement via inhibitory signals.
• 🌐 The thalamus, particularly the ventral anterior and ventral lateral nuclei, is involved in relaying motor information from the basal ganglia back to the cerebral cortex.
• 🔁 The subthalamic nuclei are part of the indirect pathway of the basal ganglia and are involved in modulating motor activity, especially to inhibit unwanted movements.
• 🚀 The substantia nigra, specifically the zona compacta, is crucial for the nigrostriatal pathway, which modulates the direct and indirect pathways by releasing dopamine.
• 🛑 The direct pathway of the basal ganglia facilitates the initiation of voluntary movements by reducing inhibition from the globus pallidus internus to the thalamus.
• 🚫 The indirect pathway works to decrease or inhibit unwanted motor activity by increasing inhibition through the subthalamic nucleus and globus pallidus internus.
• 💊 Clinical relevance includes understanding movement disorders such as Parkinson's disease, which is linked to damage in the direct pathway, and conditions like Huntington's disease affecting the indirect pathway.
• 🤖 The script emphasizes the importance of neurotransmitters like glutamate (excitatory) and GABA (inhibitory) in the functioning of the basal ganglia and their pathways.
• 🔑 Dopamine receptors D1 and D2 have opposing effects on neuronal activity within the basal ganglia, with D1 being stimulatory and D2 being inhibitory, impacting motor movement regulation.

Q & A

What are the main components of the basal ganglia?

The main components of the basal ganglia include the caudate nucleus, putamen, globus pallidus (with internal and external segments), thalamus (specifically the ventral anterior and ventral lateral nuclei), subthalamic nuclei, and the substantia nigra.

What is the striatum and which structures does it consist of?

The striatum is a structure composed of the caudate nucleus and the putamen. It plays a significant role in the direct and indirect pathways of the basal ganglia.

What is the function of the direct pathway in the basal ganglia?

The direct pathway in the basal ganglia is designed to increase or stimulate motor activity, helping to initiate motor movements.

How does the indirect pathway of the basal ganglia differ from the direct pathway?

The indirect pathway of the basal ganglia functions to decrease or inhibit motor activity, particularly unwanted or undesired movements, through a different set of neural connections involving the globus pallidus externus and the subthalamic nucleus.

What neurotransmitter is associated with the excitatory effect in the direct pathway of the basal ganglia?

Glutamate is the neurotransmitter associated with the excitatory effect in the direct pathway of the basal ganglia, released from the cortex to the striatum.

Which neurotransmitter is responsible for the inhibitory effect in the basal ganglia?

Gamma-aminobutyric acid (GABA) is the neurotransmitter responsible for the inhibitory effect in the basal ganglia.

How does the nigrostriatal pathway influence the direct pathway?

The nigrostriatal pathway influences the direct pathway by releasing dopamine onto D1 receptors in the striatum, which is stimulatory and enhances the activity of the direct pathway, promoting motor movement initiation.

What is the clinical relevance of the basal ganglia pathways in relation to Parkinson's disease?

Damage to the direct pathway of the basal ganglia, which includes the nigrostriatal pathway, can result in Parkinson's disease, characterized by difficulty initiating and maintaining motor movements due to the reduced stimulation of motor activity.

How do D1 and D2 dopamine receptors differ in their effects on the basal ganglia pathways?

D1 dopamine receptors are stimulatory, enhancing motor activity through the direct pathway, while D2 receptors are inhibitory, influencing the indirect pathway and potentially leading to decreased motor activity or increased unwanted movements.

What are some clinical conditions associated with dysfunction of the indirect pathway of the basal ganglia?

Clinical conditions associated with dysfunction of the indirect pathway include Huntington's disease, Wilson's disease, Sydenham's chorea, and extrapyramidal symptoms seen in patients taking first-generation antipsychotics.

Outlines

00:00

🧠 Basic Anatomy and Function of the Basal Ganglia

This paragraph introduces the basal ganglia, focusing on its anatomy and basic functions. It explains the orientation and components of the basal ganglia using a coronal section of the brain, identifying structures such as the caudate nucleus, putamen, globus pallidus (internal and external), thalamus, subthalamic nuclei, and substantia nigra. The striatum, formed by the caudate nucleus and putamen, and the lentiform nucleus, composed of the putamen and globus pallidus, are highlighted. The paragraph also touches on the role of the basal ganglia in motor function, emphasizing its coordination with the cerebral cortex and the corticospinal tract.

05:00

🛤️ Pathways of the Basal Ganglia and Their Motor Functions

The second paragraph delves into the pathways of the basal ganglia, discussing their role in motor functions. It outlines the direct, indirect, and nigrostriatal pathways, explaining how these pathways are integral to starting, stopping, and modulating motor movements. The paragraph simplifies the concept by describing the direct pathway as one that stimulates motor activity, while the indirect pathway is involved in inhibiting unwanted movements. The nigrostriatal pathway is mentioned as a modulatory influence on these pathways, affecting motor activity regulation.

10:01

🚀 The Direct Pathway and Its Role in Initiating Movement

This section provides a detailed explanation of the direct pathway of the basal ganglia. It describes the pathway's function in initiating and stimulating motor activity. The narrative follows the pathway from the cortex to the striatum, then to the globus pallidus internus, and finally to the thalamus, which sends signals back to the cortex. The paragraph explains the neurotransmitters involved, such as glutamate and GABA, and their roles as stimulatory and inhibitory agents, respectively. The summary emphasizes how the direct pathway facilitates the initiation of desired motor movements.

15:04

⛔️ The Indirect Pathway and Its Inhibition of Unwanted Movements

The fourth paragraph discusses the indirect pathway of the basal ganglia, which is responsible for decreasing or inhibiting unwanted motor activity. The summary outlines the pathway's route from the striatum to the globus pallidus externus, then to the subthalamic nucleus, and back to the globus pallidus internus, leading to the thalamus. It explains how the release of GABA as an inhibitory neurotransmitter along this pathway results in decreased action potentials and reduced motor activity. The paragraph also contrasts the indirect pathway with the direct pathway, highlighting their opposing roles in motor control.

20:05

🔄 The Nigrostriatal Pathway and Motor Activity Modulation

This paragraph explores the nigrostriatal pathway's role in modulating the activities of both the direct and indirect pathways of the basal ganglia. It describes how dopamine released from the substantia nigra's zona compacta influences these pathways through D1 and D2 receptors. The summary explains that dopamine's action on D1 receptors in the direct pathway amplifies motor activity, while its action on D2 receptors in the indirect pathway leads to inhibition. The paragraph also discusses the clinical relevance of these pathways, particularly in relation to Parkinson's disease, which can result from damage to the direct pathway.

25:07

💊 Dopamine Receptors in Motor Pathway Regulation

The sixth paragraph focuses on the role of dopamine receptors, specifically D1 and D2, in the regulation of motor pathways. It explains how dopamine binding to D1 receptors leads to stimulation via the G-stimulatory protein and cyclic AMP, promoting action potential generation. Conversely, dopamine binding to D2 receptors results in inhibition through the G-inhibitory protein, reducing cyclic AMP and action potentials. The summary highlights the contrasting effects of these receptors on neuronal activity and their significance in motor control.

30:08

🏥 Clinical Relevance of Basal Ganglia Pathways

This paragraph connects the basal ganglia pathways to clinical conditions, emphasizing their importance in understanding movement disorders. It discusses how damage to the direct pathway can lead to Parkinson's disease, characterized by difficulty initiating movement, while damage to the indirect pathway can result in unwanted movements, as seen in conditions like Huntington's disease and Wilson's disease. The summary also mentions extrapyramidal symptoms associated with first-generation antipsychotics and the impact of rheumatic fever on the basal ganglia.

35:10

📚 Recap and Conclusion on the Basal Ganglia

The final paragraph provides a recap of the video's content on the basal ganglia, summarizing the anatomy, function, pathways, and clinical relevance discussed throughout. It encourages viewers to like, comment, and subscribe for more educational content, and it provides links to social media and Patreon for further engagement and support. The summary emphasizes the importance of understanding the basal ganglia for medical professionals and the potential impact of related disorders on motor function.

Keywords

💡Basal Ganglia

The basal ganglia are a group of subcortical nuclei in the brain that play a critical role in a variety of motor functions, including the initiation, execution, and termination of movements. In the video, the basal ganglia are the central theme, with discussions on their anatomy, function, and pathways highlighting their importance in motor control and the consequences of their dysfunction in diseases like Parkinson's.

💡Caudate Nucleus

The caudate nucleus is one of the components of the basal ganglia, identifiable in the script as part of the striatum along with the putamen. It is involved in the cognitive and motor processes, and its dysfunction can contribute to movement disorders. The video explains its role in the striatum and its connection to the putamen as part of the basal ganglia's circuitry.

💡Putamen

The putamen is another component of the basal ganglia and is part of the striatum when combined with the caudate nucleus. It plays a role in the regulation of movement and is highlighted in the script for its connection to the caudate nucleus and its involvement in the direct and indirect pathways of the basal ganglia.

💡Globus Pallidus

The globus pallidus is divided into internal and external segments and is a key structure within the basal ganglia. It is involved in the modulation of movement, and the script describes its role in both the direct and indirect pathways, emphasizing its importance in motor control.

💡Striatum

The striatum is a collective term for the caudate nucleus and the putamen, which are involved in the selection and initiation of motor actions. The script explains that the striatum is a primary input nucleus of the basal ganglia and is central to the function of the direct and indirect pathways.

💡Lentiform Nucleus

The lentiform nucleus, also known as the lenticular nucleus, is formed by the putamen and the globus pallidus externus. It is mentioned in the script as a structure that is part of the basal ganglia and is involved in motor control and integration.

💡Thalamus

The thalamus is a complex structure that acts as a relay station for sensory and motor signals. In the context of the basal ganglia, the script specifies the ventral anterior and ventral lateral nuclei of the thalamus as being particularly important for motor function, receiving information from the basal ganglia and influencing motor activity.

💡Subthalamic Nucleus

The subthalamic nucleus is a component of the basal ganglia that is involved in the regulation of movement. The script describes its role in the indirect pathway, where it receives inhibitory signals from the globus pallidus externus and sends excitatory signals back to the globus pallidus internus.

💡Substantia Nigra

The substantia nigra is a region in the midbrain that is part of the basal ganglia's circuitry. It is known for its dopaminergic neurons, which are crucial for the modulation of movement. The script discusses the importance of the substantia nigra's zona compacta in the nigrostriatal pathway and its connection to Parkinson's disease.

💡Direct Pathway

The direct pathway is one of the three pathways of the basal ganglia and is involved in facilitating motor activity. The script explains that this pathway increases or stimulates motor activity, initiating movements, and is modulated by the nigrostriatal pathway through D1 receptors.

💡Indirect Pathway

The indirect pathway is another of the basal ganglia's pathways, which functions to inhibit unwanted or excessive movement. The script describes how this pathway decreases motor activity, particularly of undesired movements, and is influenced by the nigrostriatal pathway through D2 receptors.

💡Nigrostriatal Pathway

The nigrostriatal pathway is a dopaminergic pathway that originates in the substantia nigra and projects to the striatum. The script emphasizes its role in modulating the direct and indirect pathways of the basal ganglia, with dopamine acting on D1 and D2 receptors to either stimulate or inhibit movement, respectively.

💡Dopamine

Dopamine is a neurotransmitter that plays a crucial role in the modulation of movement through its action on the basal ganglia. The script discusses dopamine's dual role in the nigrostriatal pathway, where it can stimulate movement through D1 receptors in the direct pathway or inhibit movement through D2 receptors in the indirect pathway.

💡Parkinson's Disease

Parkinson's disease is a neurodegenerative disorder characterized by tremors, stiffness, and difficulty with movement. The script explains the connection between Parkinson's disease and damage to the direct pathway of the basal ganglia, particularly the loss of dopaminergic neurons in the substantia nigra.

💡Huntington's Disease

Huntington's disease is a hereditary neurodegenerative disorder that leads to uncontrolled movements and cognitive decline. The script mentions Huntington's disease in the context of damage to the indirect pathway of the basal ganglia, which can result in unwanted motor movements.

Highlights

Introduction to the basal ganglia, covering anatomy, function, and pathways.

Explaining the orientation and components of the basal ganglia using a coronal section of the brain.

Identification of the caudate nucleus, putamen, globus pallidus, thalamus, subthalamic nuclei, and substantia nigra as key components of the basal ganglia.

Clarification of the striatum as a collective term for the caudate nucleus and putamen.

Description of the globus pallidus's internal and external segments and their roles.

Differentiation between the ventral anterior and ventral lateral nuclei of the thalamus in the context of the basal ganglia.

The role of the basal ganglia in motor function, including initiating, stopping, and modulating movement.

Overview of the direct pathway in the basal ganglia and its function to stimulate motor activity.

Mechanism of the direct pathway from cortex to striatum, globus pallidus internus, and back to the cortex.

Explanation of neurotransmitters glutamate and GABA in the context of the direct pathway.

Introduction to the indirect pathway and its role in decreasing unwanted motor activity.

Detailed pathway of the indirect route from cortex to striatum, globus pallidus externus, subthalamic nucleus, and back to the cortex.

The nigrostriatal pathway's influence on modulating the activities of both the direct and indirect pathways.

Impact of dopamine and its receptors (D1 and D2) on the modulation of motor activity in the basal ganglia.

Clinical relevance of the basal ganglia pathways in movement disorders such as Parkinson's disease and Huntington's disease.

Summary of the video content, emphasizing the importance of understanding the basal ganglia for clinical applications.

Transcripts

iron engineers in this video today we

are going to talk about the basal

ganglia we'll go over the basic anatomy

basic function and then really dig into

some of the pathways direct

indirect and then that striatal

pathway and we'll have a little tidbit

on the clinical relevance

in these basal ganglia lesions all right

ready let's go ahead and get started

all right ninja nurse so let's go ahead

and start off talking about the basic

anatomy of the basal ganglia so i want

to cover two points one is kind of the

orientation of the basal ganglia

and then the components of the basal

ganglia right so what we're doing here

is we're taking a coronal section so i'm

taking here i'm slicing the brain here

pulling off the anterior piece and

looking at the posterior piece

in this fashion there's a bunch of

different components here

okay the first component that i want you

to know here that we're going to label

one

this is called the caudate nucleus okay

the caudate nucleus

okay the second part that i want you to

know here is this one here in red

this right here is called the putamen

this is called the putamen

then the next one is this entire big

blue hunk of cheese here what is this

thing called

this is called your globus pallidus but

there's actually two parts

an internal part and an external part

okay so we have the caudate nucleus

putamen and the globus pallidus

internal external component what else is

next

the next part is here these little pink

little egg

shaped structures on this and in on the

sides of the

third ventricle this blue structure here

is the third ventricle a little

fluid-filled space with cerebrospinal

fluid

on the sides of it are your thalami so

your thalamus is one of the

other components of the basal ganglia

the next component here is going to be

these

green structures here that's kind of a

little bit inferior to the

thalamus these are called your

subthalamic nuclei

these are called your subthalamic nuclei

and the last

component of the basal ganglia is

actually in the midbrain

right in the midbrain you have this very

special structure here

called the substantia

so we know the basic components of the

basal ganglia and their orientate

orientation in a coronal section

now let's name them and a couple other

little specifics

all right beautiful so we know the

components right but let's really write

out their names plus there's a couple

other terminology that we have to

establish

so the first component that we mentioned

as a part of the basal ganglia

is called the caudate nucleus

so this is called the caudate nucleus

very interesting structure

the next one we said the second

component this red structure

is called the putamen now this is very

important the reason why i want to kind

of make uh some terminology here

is that whenever you take the caudate

nucleus and the putamen

them together collectively

they make a structure called

the striatum

okay so they make a structure called the

striatum so i want you guys to remember

that the putamen

and the caudate nucleus combine make up

the striatum

all right beautiful the next thing the

third component that we mentioned

is the globus

pallidus right and we said that there

was two components

what kind of components there was a

internal component so we're going to put

globus pallidus in turnis and then there

was an

external component which is called the

globus pallidus

externus so again this is globus

pallidus internis

globus pallidus externus okay

now there's another term that we have to

establish

if you take the putamen and combine it

with the globus pallidus this makes a

very special type of name or structure

and we call this the lentiform

nucleus okay so the caudate and the

putamen make the striatum and the

putamen and the globus pellitus make up

the

lentiform nucleus beautiful all right

the next thing that we have to discuss

with my pink marker here is the fourth

component which is the

thalamus so this is our thalamus but i

actually want to be a little bit

specific i know you guys remember from

the thalamus video

there was two motor nuclei dig into your

cerebral cortex

what were those thalamic nuclei that we

were really

actually focusing on here do you

remember it was the

ventral anterior nucleus

of the thalamus and the ventral

lateral nucleus of the thalamus

so when we say that the thalamus is a

part of the basal ganglia

if we're really being particular it's

actually the ventral anterior and

ventral lateral nucleus of the thalamus

are beautiful the fifth component

the fifth component here of the basal

ganglia is called what

this is called your subthalamic

nucleus okay so

now we talked about these main ones

remember we talked about there was

one last component the sixth component

what is this this is very important

what is this final structure here this

final structure here is called the

substantia so what are these

called here

this is called both of these is your

substantia

now the one that we there's two

parts of it we talked about right

we're just going to abbreviate them zona

compacta and zona

reticularis the one that we care about

in this pathway is the zona compacta

that's the one that contains all that

dopaminergic neurons

okay so we've established the components

we've established some

specific terminology that i might use

throughout the course of this video

the last thing i want us to talk about

before we get into the pathways is the

basic

motor function obviously i kind of give

you the idea what the basal ganglia is

involved in

its motor function so the motor function

is coordinated by the cerebral cortex

right so if you guys remember we have a

couple different regions in the cerebral

cortex that are involved in motor

movement

here's your central sulcus right this

black line here behind the central

sulcus you have the postcentral gyrus

which is your primary

somatosensory cortex and then

anterior to this you have your

precentral gyrus which is where your

primary motor cortex is

and then out just kind of anterior to

that you have your

pre-motor cortex right

okay so you have your

primary motor pre-motor cortex and your

primary somatosensory cortex

these areas kind of combined make up

your basically your entire kind of motor

cortices

these structures they decide your

voluntary motor movement

right what happens is is they send

information down from these areas to

your

muscles via these upper motor neurons

down to your

lower motor neurons which go to your

skeletal muscles

and cause your skeletal muscles to

contract right so this is called your

corticospinal tract

well in order for this motor plan to go

down to the muscles you have to

uh kind of have communication with the

basal ganglia so what i'm going to do

here is in the kind of like this green

structure here i'm going to imagine that

this is the

basal ganglia here okay so imagine for a

second this is our

basal ganglia these cerebral cortex

areas

have to communicate their motor plan

with the basal ganglia

the basal ganglia will take that motor

plant and modify it in a particular way

and send it back to the cerebral cortex

to send now the proper motor plan

to start movement stop movement or

modulate movement

what did i just say what were the three

primary functions of the basal ganglia

to start movement

stop movement and modulate

motor movement so this is all involved

with movement so it's designed to kind

of start or initiate a movement

stop kind of unwanted motor movements

and

modulate motor movements beautiful

now let's get into the pathways all

right so now we got to do is since we've

already talked about the basic anatomy

the basic function of the basal ganglia

we really got to kind of expand on that

function a little bit more and talk

about

three particular pathways the direct

pathway

indirect pathway and the niagara

striatal pathway

the reason why they're important is they

basically tell us the three functions

to start movement to stop movement

or to modulate movement in some way so

the first pathway that we have to

discuss here

is called the direct pathway now let's

keep it relatively simple here when we

talk about the direct

pathway what i want you to know

in the most simplistic way is that this

is designed to

increase or stimulate motor

activity that is honestly the easiest

way or

if you want to expand on that it's

designed to help to initiate

motor movements but i just like to think

about it as increasing or

stimulating motor activity

how does it do that well there's a

pathway here right let's let's provide

the basic

kind of like scaffolding of this pathway

remember i told you

that in order for the cortex where you

have your motor cortex

it is going to send down a motor plant

to your skeletal muscles right

but in order for it to do that it has to

send it to your basal ganglia basal

ganglia will then take that information

and send it back up to the cortex to

completely modify that motor plant

so we have to go from the cortex to the

basal ganglia back to the cortex

how does that look well here you have

neurons in your cortex

right and what they're going to do is

they're going to send their axons down

to the striatum do you guys remember

what the striatum was

it was made up of the putamen and the

caudate nucleus

then the neurons from the putamen and

the caudate nucleus

will then move towards the globus

pellitus

internus then from the globus politus

internist these neurons will then go to

the

thalamus and you know in the thalamus

you have the particular types of nuclei

here called the ventrolateral

and ventral anterior nuclei their axons

will then

extend back up to the cerebral cortex

so this is basically the basic

scaffolding of the

cerebral cortex involvement with the

direct pathway of the basal ganglia

now let's dig into this pathway a little

bit more okay we got to go over kind of

the mechanic you know the nitty gritty

stuff

from the cortex to the striatum these

types of fibers are called

glutaminergic fibers what does that mean

that means that the neurotransmitter

that these red fibers release

onto these blue neurons is actually

based on a neurotransmitter called

glutamate

we'll go over a little bit more of the

detail of this but for right now

the simplistic way that i want you to

remember this is that glutamate is a

stimulatory

neurotransmitter so when it acts on the

next neuron the postsynaptic neuron

it's going to activate it okay so if

that's the case then

this neuron is firing lots of action

potentials down

from the cortex to the

striatum right and then what is it going

to do

it's going to release glutamate which is

going to stimulate the neurons present

within the

striatum right if that's the case

these neurons are going to be super

active and they're going to send

lots of action potentials down their

axons from

the striatum to where so the globus

pellitus

internus the neurotransmitter that's

being released

from the striatum to the globus politus

internus

is actually gaba gamma amino butric acid

what i want you to remember we'll go in

more detail later

but simplistically it is a inhibitory

neurotransmitter

so when it is released from this neurons

coming from the striatum onto the globus

pellitus internus it's going to inhibit

that neuron so if we release

a lot of gaba because this is sending

lots of action potentials

it's really going to inhibit this globus

pellitus and turnus

now the neurons going from the globus

polytus and turns to the thalamus

they're going to have

decreased action potentials right

and if there's decreased action

potentials that means that there's

less neurotransmitter released from the

globus pellitus internist onto the

thalamus

now the type of neurotransmitter that's

released here

between the globus polyitis internas and

the thalamus is again

gaba which is a inhibitory

neurotransmitter now

if i'm having less action potentials i'm

releasing

less gaba onto the thalamic nuclei gaba

is an inhibitory neurotransmitter

if i have less gaba being released here

that means i have less

inhibition so if there's less inhibition

this is sometimes referred to as

disinhibition or it's released from

inhibition and now

these neurons in the thalamus are going

to be stimulated

and if they are stimulated

they're going to send lots of action

potentials

back up to your motor cortex

and the end goal is that now from your

motor cortex

going down to your skeletal muscles

what is it going to do it's going to

increase

the motor activity of the desired

skeletal muscles

isn't that cool how the direct pathway

does that so

that's what i want you to remember for

the basics now we talked about glutamate

gaba a lot

let's go over the basic ways that these

are inhibitory and stimulatory

neurotransmitters down here in the

bottom

all right so now let's go over the

neurotransmitters a little bit more now

remember i said gaba

right so gaba is a inhibitory

neurotransmitter let's expand on that a

little bit gaba has different types of

receptors we're not going to go into the

details of but there is a b and c

but what i want you to know here the

main thing that we're talking about is

that gaba binds on to what's called

these

ligand-gated ion channels so here's your

gaba

it'll bind on to a particular neuron

right so here's your postsynaptic neuron

in this case

gabel will then bind onto this receptor

when it binds onto this receptor what

it'll do is

let's say the before there was like a

little

kind of like thing here a gate blocking

the entry of ions

when gaba binds what it does is is it

opens up that gate and allows for what

certain types of ions to move in or out

now if that's the case then it has to be

inhibitory right so what happens is very

interesting

but positive ions like potassium can

leave

this neuron or negative ions like

chloride can

enter this neuron either way i'm losing

positives

or i'm gaining negatives what's the

overall result inside of the cell

the cell is going to become extra

negative

if the cell becomes extra negative i

take the resting membrane potential

and drop it below way below the resting

membrane potential what is that called

whenever you drop the voltage below the

resting membrane potential

it's called hyper

polarization and this type of

hyperpolarization is actually called an

i p s p

an inhibitory postsynaptic potential

so that is how this does that and so

there's going to be no action potentials

carried down this neuron because of how

gaba works

in the same way we talked about

glutamate

and how glutamate we said in the most

simplistic sense

is a stimulatory neurotransmitter the

same concept happens here

glutamate binds onto this ligand-gated

ion channel

generally the gate is closed whenever

that ligand is not bound

but when glutamate binds it opens up the

gate

and then allows for positive ions to

flow in maybe positive ions like sodium

maybe positive ions like calcium and

these ions will flow

into the cell and cause the cell to

become

extra positive as you increase the

positive voltage in the cell what do you

do

you take resting membrane potential and

move it towards

threshold potential and whenever you hit

a particular threshold inside of the

cell

that may trigger a action potential

so this is referred to as a e

p s p so glutamate

has a stimulatory effect via this

mechanism

and gaba has an inhibitory effect via

this mechanism

okay now that we've established the

basic concepts of that with the direct

pathway

we can blast through the indirect

pathway all right

so now we talked about the direct

pathway designed to stimulate motor

movement start motor movement initiate

motor movement what's the other function

of the basal ganglia

it's designed to inhibit motor activity

in other words and

particularly inhibit unwanted

motor movements undesired motor

movements

so the other function of the basal

ganglia is carried out via the

via the activity of the in direct

pathway of the

basal ganglia and again the basic

function i want you to easily remember

this is

to decrease motor activity

or inhibit motor activity but

particularly if we're really digging

into the detail

it's inhibiting or decreasing unwanted

let's actually add that in

decreasing unwanted

or undesired motor activity

i really want us to understand that okay

so same concept we've got to communicate

from the cortex to the basal ganglia

back to the cortex

but it's just a different route let's

build our scaffolding for this

so coming from the cortex we're going to

have neurons going to the striatum

same thing like we have with the direct

pathway they're going to act on the

neurons present within the

striatum then from the neurons of the

striatum

instead of them glowing to the globus

pilitis internus

they go to the globus politis

externus then

from the globus politus externus these

neurons will then move

downwards to the

subthalamus right the subthalamic nuclei

one of the other components of the

basal ganglia then

from the subthalamic nucleus

it will have neurons that will go

back up to the globus pallidus

but to the internal component of the

globus pallidus

then from the neurons of the globus

pallidus internis which

are acted on by the subthalamic nuclei

it will then go to the

thalamus what type of nuclei of the

thalamus are we saying

particularly the ventral anterior and

ventral lateral nuclei of the thalamus

and then the fibers from these are sent

back up to the

cortex this is our basic scaffolding now

let's dig

into it again neurons coming from the

cortex to the striatum

what type of neurotransmitter are

released here

this is glutamate

glutamate is what an a stimulatory

neurotransmitter so what is it going to

do it's going to stimulate

these neurons present within the

striatum

what does that mean if they're

stimulated there's going to be lots of

epsps and lots of action potentials

being

traveling down these axons from where

from the striatum to the globus politis

externus now these neurons release

gaba gaba is a inhibitory

neurotransmitter

if there's lots of action potentials

that means lots of gaba is being

released here

if lots of gaba is being released onto

this neuron this neuron is going to be

heavily

inhibited if it's inhibited via the

ipsps in hyperpolarization

then this neuron when it's inhibited

it's going to send

less action potentials

from the globus pallidus externus to the

subthalamic nuclei so decrease action

potentials

if there's decreased action potentials

going from the globus polytus externus

to the subthalamic nucleus guess what

type of neurotransmitter is released

here onto the subthalamic nucleus what

type of neurotransmitter is being

released here

gaba and what do we say gaba is gaba is

a

inhibitory neurotransmitter so what

happens here is that means that we're

releasing

less gaba now remember what do we say

whenever there is less

gaba that means there is decreased

inhibition

decreased inhibition is kind of what's

called disinhibition

which means that this neuron is released

from inhibition and is actually

stimulated now because this neuron the

subthalamic nucleus a neuron is actually

stimulated what's it going to do

send lots of action potentials

from the subthalamic nucleus to the

what the nucleus are neurons present

within the globus pellitus internus

if there's lots of action potentials

going from the subthalamic nucleus

to the globus pallidus internist that

means lots of neurotransmitters being

released here

what type of neurotransmitters being

released here glutamate

glutamate is a stimulatory

neurotransmitter that means you're going

to have heavy

stimulation of these neurons present

within the globus pallidus internis

if there's heavy stimulation of the

neurons on the globus pallidus

internist that means that you're going

to have increased activation and

increased

action potentials traveling down this

neuron

if there's increased action potentials

between the neurons from the globus

pallidus internus

to the thalamus that means lots of

neurotransmitters being released here

what type of neurotransmitter is being

released here gaba

gaba is a inhibitory neurotransmitter

so that means lots of gaba is going to

be released onto the thalamic nuclei

if lots of gaba is released that means

strong inhibition of these

thalamic nuclei that means

that from the thalamus if there's

decreased stimulation of the thalamus

that means that these thylamic nuclei

are going to send decreased action

potentials via their axons to the

cortex and if there's decreased action

potentials going to the cortex guess

what

that's going to tell the motor cortex

that we want to

decrease particular motor activity of a

given body part

doesn't that make sense so that's how

the indirect pathway

is more particularly when we really get

down to the nitty-gritty

is actually working now we talked about

initiating motor movement

preventing unwanted motor movement or

stimulating decreasing motor activity

now we got to talk about how we can

modulate the activity of both

the direct and indirect pathway let's

come over to this last part

all right so the last function of the

basal ganglia remember i told you that

it's actually kind of a

modulation type of action the particular

name of this pathway that we have to

discuss here is called the

nigro striatal

pathway all right so the nigrostriatal

pathway is technically

really important and it's involved

within what the modulation

okay of the direct

and indirect pathway

so it's going to modulate the activities

now the best way i like to remember the

nigro stradal pathway

is it's trying to amplify the activity

of movement

so how does it actually kind of modulate

the direct and indirect pathway the

really the

the particular way that i want you to

remember is that it's designed to kind

of amplify

motor activity to really kind of

stimulate it

how does it do that well let's first

talk about how it influences the direct

pathway

and then how it influences the indirect

pathway

okay so again have your scaffolding we

can actually kind of blast through this

from the cortex coming down to the

striatum then from the

striatum to the globus pallidus

internist from the globus pallidus

internist to the

thalamus from the thalamus we go back to

the

via the two nuclei back to the cortex

right so this is our basic scaffolding

now here's where we add in this extra

pathway

remember we had the substantia

right

well what happens is from the actually

the zona compacta

you have neurons that actually ascend

upwards

and go to the

striatum we're going to kind of loop

this one here

and what they do is they release

dopamine onto the actual

neurons of the striatum now the

type of a dopamine receptor is actually

what's really specific

what i want you to remember is the

dopamine receptor here is actually a d1

receptor okay and what i want you to

remember right now is that this is a

stimulatory receptor we'll talk about a

little bit how that

actually is happening but again it's the

same neurotransmitter in both pathways

it's just the receptor that's different

in both pathways

so d1 receptor is important for direct

pathway in its stimulatory

okay so what does that mean right okay

so let's follow this down from the

cortex coming down to the

striatum what did we say we were

releasing glutamate glutamate is

stimulating

these neurons right on top of that you

also have

this dopamine that's also being released

and what do we say dopamine is acting on

the d1 receptors on these nuclei and

also stimulating them

now you have an extra kick or stimulus

coming from the cortex

and from the substantia now

these neurons these neurons going from

here it is these neurons going from the

striatum to the globus pellitus

internist are going to fire like a mofo

and they're going to send tons and tons

and tons of action potentials

really really powerfully to the globus

pallidus internus

what does that mean the neurotransmitter

that's released here

it's it's actually going to be released

in large amounts onto this globus

pelitus internist

what's that neurotransmitter gaba if

there's lots of gaba

there's lots of inhibition

so that means that this nucleus here

right to this nucleus this

nucleus of the globus polytus and

internus is going to be super

let's make a big negative sign super

inhibited

that means it's going to send very

little action potentials

very little action potentials from the

globus politis and turnus to the

thalamic nuclei

if there's very little here we're going

to make like a teensy little arrow very

little gaba

or here we'll do this lots of down

arrows if there's

very little gaba released there is a

significant decrease

in inhibition right

so if there's a significant decrease in

inhibition that's going to result in

extra stimulation of the thalamic nuclei

so again less action potentials less

gaba

less inhibition more than normal on the

thalamic nuclei

now those thylamic nuclei are released

from inhibition significantly

and they're going to fire like a mofo

and they're going to send lots and lots

and lots of action potentials back up to

the

cerebral cortex telling that cerebral

cortex stimulating it and then doing

what

what was already normal increase in

motor activity

it's going to increase the motor

activity

even more so it's going to want to

really help to start

motor movements why is this so

important whenever there's damage

of the direct pathway in some way shape

or form

where you want to increase motor

activity if you

damage this pathway right particularly

damaging the substantia you know

what disease can result that from this

parkinson's disease so the clinical

relevance here

is with respect to a particular disease

called parkinson's disease

right so parkinson's disease what's kind

of the characteristic of this

they have difficulty initiating movement

maintaining movement

right why because you've damaged the

the direct pathway with the nigrostratal

involvement and now what you're supposed

to be doing to increase motor activity

now you can't perform that motor

activity very well and so that's kind of

one of the classic things that i want

you to remember so direct pathway with

involvement of the niger striatal

pathway damage of that pathway can

result in

parkinson's disease okay beautiful now

let's talk about how the striatal

pathway influences the

indirect pathway all right so next one

is the

involvement of the niger striatal

pathway with the indirect pathway

okay so again get build your scaffolding

right so from the cerebral cortex to the

striatum

right then from the striatum

this is also a good recap right good

review from the striatum to the globus

politis

externus from the globus politus

externus to the

subthalamic nucleus from the subthalamic

nucleus back

up to the globus politis

in turnus and from the globus politis

internist to the

thalamic nuclei particularly ventral

anterior

and ventral lateral thalamic nuclei and

then from here back up to the

cortex good we've built our scaffolding

now we have to add in that next extra

pathway what's that next extra pathway

that we said is really important here

that's coming from the substantia

the nigrostriatal pathway

again neurons from the zona compacta

come here and send axons onto the

striatum

so the neurons of the putamen and we'll

hear kind of loop this around here

and neurons of the caudate nucleus now

the type of receptors present on the

striatum

in this indirect pathway okay is

actually called what d2 receptors

d r2 receptors what i want you to

remember here is that they are

inhibitory okay we'll talk about how

they do that but i just want you to

remember

where dopamine is released onto these

neurons within the indirect pathway

it's going to cause inhibition all right

now let's follow this pathway from the

cortex what do you have what do we say

you're releasing lots of glutamate on

the to the striatum right

glutamate has a stimulatory effect onto

these

neurons but then you have dopamine

that's being released onto the d2

receptors here of the striatum what's

that trying to do

that's trying to inhibit these neurons

so now think about this you have normal

stimulation

but then coming from the substantia

you have

increasing inhibition

what does that mean well normally you'd

be sending lots of action potentials

from the stratum to the globus politus

externus

but because we have some inhibition to

these neurons

now there's going to be decreasing

action potentials

so now what used to be a lot of action

potentials is

decreasing action potentials moving from

the striatum to the globus pellitus

externus

what does that mean that means less

neurotransmitter is released here what

kind of neurotransmitter is released

here

gaba gaba is inhibitory

so if there's less action potentials

that means less gaba

less gaba means less inhibition

if there's less inhibition of this

neuron it means it's disinhibited

and it will be stimulated and fire

so now this neuron is going to fire more

and it's going to send

increasing action potentials from

the globus pallidus externus to the

subthalamic nucleus

if there's increasing action potentials

that means that there's increased

neurotransmitter released here

what type of neurotransmitter is

released here gaba

gaba is inhibitory so if there's lots of

gaba released onto the subthalamic

nucleus what does that mean

that means that there is increasing

inhibition because gaba is an inhibitory

neurotransmitter

if that's the case then what does that

mean

that means well i have two red markers

that means that if there's

a lot of inhibition here there is

decreasing action potentials carried

from the subthalamic nucleus

to the globus pellitus internus

if there's decreasing action potentials

that means less neurotransmitter is

released

what type of neurotransmitter is

released here glutamate

if there's less glutamate what does that

mean that means that there's less

stimulation if there's less stimulation

of this neuron then we can now kind of

say that it is actually

slightly inhibited and so that means

that there's going to be

decreasing action potentials

moving from the globus politis internist

to the

thalamus if there is decreasing action

potentials going from the globus politus

and

is to the thalamus that means less

neurotransmitter is released here

less neurotransmitter like which one

gaba

if there's decreasing gaba that means

there's decreasing

inhibition so if there's decreasing

inhibition that's called

disinhibition so it's released from

inhibition

and now it's going to be stimulated

and now these thalamic nuclei are going

to do what

they're going to fire like a mofo and

send increasing action potentials now

that they're released from inhibition

up to the cerebral cortex so now the

cerebral cortex is going to be

stimulated

and now the motor activity that you were

designed to decrease

now you're going to increase the

activity the motor

activity but again what type increase

the motor activity of

particularly maybe unwanted

motor movements

okay so you're going to increase the

motor activity of the

unwanted motor movements and in the

direct pathway it also

increases the activity of wanted motor

movements

all right so the last thing that i

wanted to talk about is remember i said

that there was a little discussion here

with the d1 receptors and d2 receptors

again so we're going to say here we're

going to talk about the d1 receptor

and we said that this is a stimulatory

type of receptor

and then over here we're going to talk

about the d2 receptor and we said how

this is a

inhibitory receptor let's explain this

very basically

okay so dopamine right it's the same in

both of these pathways it's the same

neurotransmitter that's released

but when it binds onto that d1 receptor

right the thing is it binds onto a g

protein couple receptor particularly a

g-stimulatory protein

and if you guys remember from the the

plethora videos that we've done

g-stimulatory leads to an

increase eventually in cyclic amp

cyclic amp will then do what it'll

activate protein kinases

and these protein kinases will do what

will the phosphorylate particular

channels

and allow four positive ions to flow

into the cell

leading to stimulation of increasing

voltage

inside of the cell so normally you have

a resting membrane potential

if you bring in lots of positive ions

that'll bring it to threshold potential

if you bring it to threshold potential

eventually you'll activate voltage-gated

channels in the axon and lead to a

action potential okay so the d1

receptors that's how they function is by

increasing cyclic amp

guess what the d2 receptors are just the

exact opposite

they work via the g-inhibitory protein

and g-inhibitory protein will actually

do what to cyclic amp

it will decrease the cyclic amp levels

that means decrease

protein kinase levels that means

decreased phosphorylation of

channels in the membrane and that means

what

less positive ions are moving in here

if less positive ions are moving into

the cell

that means that you're going to have a

difficult time of getting that resting

membrane potential to threshold

potential

right and so because of that this won't

be able to reach

threshold potential and therefore it

will actually lead to

decreasing action potentials moving down

this neuron

okay so that's kind of the basic that i

want you guys to understand with the

dopamine receptors

so i wanted to take a quick little time

to just kind of again

recap bring a clinical point of the

basal ganglia why why are we learning

this right so we talked a little bit

about parkinson's disease

i kind of wanted to expand on that just

a little bit more and provide a little

bit more clarification

so remember when we talked about direct

pathway that was designed to increase

the you know the motor activity to start

motor activity to initiate motor

activity

well what happens if you damage the

direct pathway which wants to

start initiate perform motor activity

well now you have difficulty in being

able to initiate start and maintain

motor activity there's a particular

disease

process and this is called parkinson's

disease right so we kind of

touched on that a little bit right

in the same concept the indirect pathway

is designed to

decrease motor activity but particularly

unwanted

motor activity so now the indirect

pathway

right if it's designed to decrease motor

activity so to prevent unwanted motor

movements

right so if you damage this pathway you

damage the indirect pathway

this can result in unwanted motor

movements right

and these can lead to conditions

particularly like

huntington's disease huntington's

disease or you know there's another

condition

where if you have a lot of copper built

up in the liver the liver stops

functioning and then it can lead to

damage to the actual

central nervous system is called

wilson's disease

also known as apato lenticular

degeneration or

in someone who has rheumatic fever you

know in rheumatic fever we talked about

how

they can have what's called syndenham's

chorea where the antibodies can attack

the actual basal ganglia the other thing

that's actually really interesting

is drugs there's what's called extra

pyramidal

syndrome particularly common in patients

who taking

first generation antipsychotics right

what happens is that really alters this

pathway

particularly the d2 receptors and can

lead to problems like tardive dyskinesia

right it can lead to acathy which is

kind of like a restless movement

it can lead to dystonic reactions okay

so this is kind of important to provide

a clinical correlation of the basal

ganglia

with particular types of hypokinetic

movement disorders and hyperkinetic

movement disorders

okay all right so that covers the basal

ganglia all right ninja nurse so in this

video we talk about the basal ganglia

the anatomy the function the pathways

and a little bit about the clinical

relevance i hope you guys like this

video i hope you guys learned a lot and

enjoyed it if you guys did hit that like

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