basal ganglia

What are the four main nuclei of the basal ganglia circuit?

Striatum, Globus Pallidus (GP), Subthalamic Nucleus (STN), and Substantia Nigra (SN)

What are the two main pathways in the basal ganglia?

The Direct (D1) Pathway and the Indirect (D2) Pathway

What is the net effect of the Direct (D1) Pathway?

Facilitates and initiates movement

What is the net effect of the Indirect (D2) Pathway?

Suppresses and inhibits movement

What is the first step in the Direct Pathway?

Cortex sends excitatory GLU signal to D1 Medium Spiny Neurons in Striatum

What do D1 MSNs do when activated?

They release GABA, inhibiting the GPi/SNr

What happens when GPi/SNr are inhibited?

They stop their tonic inhibition of the Thalamus (Disinhibition)

What does the Thalamus do when disinhibited?

It sends excitatory signals to the Motor Cortex to drive movement

What is the first step in the Indirect Pathway?

Cortex sends excitatory GLU signal to D2 Medium Spiny Neurons in Striatum

What do D2 MSNs do when activated?

They release GABA, inhibiting the GPe

What happens when GPe is inhibited?

It stops its tonic inhibition of the Subthalamic Nucleus (STN)

What does the STN do when disinhibited?

It becomes active and sends excitatory GLU signals to the GPi/SNr

What happens when GPi/SNr are excited by the STN?

They increase their GABAergic inhibition of the Thalamus

What is the final result of the Indirect Pathway?

Thalamus is strongly suppressed, preventing movement

Where does dopamine come from?

Substantia Nigra pars compacta (SNc)

What does dopamine do to the Direct (D1) Pathway?

Excites it (facilitates movement)

What does dopamine do to the Indirect (D2) Pathway?

Inhibits it (facilitates movement by reducing suppression)

What type of receptor does dopamine use on the Direct Pathway?

D1 receptors

What type of receptor does dopamine use on the Indirect Pathway?

D2 receptors

What is the overall role of dopamine in the basal ganglia?

To promote movement by exciting the GO pathway and inhibiting the STOP pathway

What happens in Parkinson's disease to dopamine?

Dopamine neurons in SNc die

What is the effect on the Direct Pathway in Parkinson's?

Reduced excitation, less "GO" signal

What is the effect on the Indirect Pathway in Parkinson's?

Reduced inhibition, more "STOP" signal

What is the net result in Parkinson's?

Poverty of movement (Hypokinesia)

What is Disinhibition?

The process where inhibiting an inhibitory neuron leads to excitation

Where does disinhibition occur in the Direct Pathway?

When Striatum inhibits the inhibitory GPi/SNr, freeing the Thalamus

What is the key neurotransmitter for inhibition in the basal ganglia?

GABA

What is the key neurotransmitter for excitation from the cortex?

Glutamate (GLU)

What structure acts as a "brake" on the thalamus?

GPi and SNr

What structure acts as a "brake booster" in the Indirect Pathway?

Subthalamic Nucleus (STN)

What is the effect of STN lesions?

Hyperkinesia (e.g., Hemiballismus - wild flinging movements)

Why does an STN lesion cause excessive movement?

Because it can't excite GPi/SNr, so the thalamus is permanently disinhibited

What is the main subject of this document?

The modulation of movement by the Basal Ganglia

What are the two main subcortical systems that communicate with the thalamus for motor control?

The Basal Ganglia and the Cerebellum

What are the two main output pathways from the brain for motor control?

The Pyramidal system and the Extrapyramidal system

Do the basal ganglia have direct connections to lower motor neurons?

No

How do the basal ganglia influence movement?

They modulate the activity of upper motor neurons

List the five main components of the basal ganglia and associated nuclei

Striatum, globus pallidus, amygdala, subthalamic nucleus, and substantia nigra

What are the four main nuclei of the basal ganglia circuit?

Striatum, Globus Pallidus (GP), Subthalamic Nucleus (STN), and Substantia Nigra (SN)

What are the two main parts of the striatum?

Caudate nucleus and Putamen

What is the ventral striatum also known as?

Nucleus Accumbens

What are the two segments of the Globus Pallidus?

External segment (GPe) and Internal segment (GPi)

What are the two parts of the Substantia Nigra?

Pars reticulata (SNr) and Pars compacta (SNc)

What type of neurons are in the Substantia Nigra pars compacta?

Dopamine (DA) neurons

What is the first main function of the basal ganglia?

Selection and initiation of intended movements for smooth execution of sequences

What is the second main function of the basal ganglia related to learning?

Signaling aspects of learning and reinforcement (error signal)

What is the third main function of the basal ganglia?

Procedural learning and habit formation

What other factors besides motor execution are the basal ganglia involved in?

Motivation and Context

What does the "Status" monitoring involve for movement?

Monitoring body position, movement speed, and sensory feedback

What are the two parts of the dorsal striatum?

Caudate nucleus and Putamen

What is the name of the pathway that brings inputs to the striatum?

Corticostriatal pathway

Where do the inputs to the striatum come from?

All association cortices (frontal, parietal, temporal)

What part of the striatum receives input for eye movement control?

Caudate nucleus

What part of the striatum receives input from sensory and motor cortices?

Putamen

What are the two main parallel pathways within the basal ganglia?

D1 and D2 pathways

What is the main type of projection neuron in the striatum?

Medium Spiny Neurons (MSNs)

What percentage of striatal neurons are Medium Spiny Neurons in humans?

80%

What neurotransmitter do Medium Spiny Neurons use?

GABA (inhibitory)

What are the two main types of local circuit neurons in the striatum?

Medium aspiny cells (GABA) and Giant aspiny cells (Acetylcholine)

What do Medium Spiny Neurons (MSNs) integrate?

Inputs from many cortical neurons, plus local, thalamic, and dopaminergic inputs

Where does the main output from the Putamen go?

Globus Pallidus

Where does the main output from the Caudate go?

Substantia Nigra pars reticulata

What is the primary excitatory neurotransmitter input to the basal ganglia?

Glutamate (Glu) from the cortex

What is the primary modulatory neurotransmitter input?

Dopamine (DA) from the Substantia Nigra pars compacta

What is the primary intrinsic neurotransmitter of the basal ganglia network?

GABA (inhibitory)

What is the default (tonic) activity of the output nuclei (GPi/SNr)?

They tonically inhibit their targets

What is the effect of the basal ganglia's tonic inhibition?

It prevents unwanted movement

How is a movement initiated in the basal ganglia circuit?

Via disinhibition (cortex excites MSNs, which inhibit GPi/SNr, releasing the thalamus)

What is the net effect of the Direct Pathway?

It facilitates or initiates movement

How does the Direct Pathway facilitate movement?

Striatal MSNs inhibit GPi/SNr, which disinhibits the thalamus

What is the net effect of the Indirect Pathway?

It inhibits movement

How does the Indirect Pathway suppress movement?

It ultimately increases inhibition from GPi/SNr onto the thalamus

What is dopamine's role in the Direct Pathway?

It excites the pathway via D1 receptors

What is dopamine's role in the Indirect Pathway?

It inhibits the pathway via D2 receptors

What is dopamine's overall effect on movement?

It promotes movement

What are three types of motor disturbances in basal ganglia disorders?

Tremor/involuntary movements, changes in posture/tone, poverty/slowness of movement

What is the term for diminished movement?

Hypokinesia

What is the term for excessive movement?

Hyperkinesia

Name a disease associated with hypokinesia

Parkinson's disease

Name a disease associated with hyperkinesia

Huntington's disease

What is the primary cause of Parkinson's disease?

Loss of dopamine neurons in the Substantia Nigra pars compact