week 4 basal ganglia

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Questions and Answers

What role does the basal ganglia have in relation to thalamic activity?

It has no influence on thalamic function.

It exclusively activates thalamic neurons.

It always increases thalamic activity.

It selectively regulates thalamic inhibition depending on inputs. (correct)

Which statement accurately describes the function of medium spiny neurons in the putamen?

They are solely responsible for unwanted movements.

They require multiple excitatory inputs to activate. (correct)

They respond only to visual stimuli.

They operate independently from cortical influences.

How do caudate neurons differ from putamen neurons during movement anticipation?

Caudate neurons are inactive during anticipation.

Both caudate and putamen neurons have identical firing patterns.

Caudate neurons fire before eye movements. (correct)

Caudate neurons fire prior to limb movements.

What does anticipatory discharge from striatal neurons indicate?

The decision to move toward a goal. Signup and view all the answers

What is the primary function of the indirect pathway in the basal ganglia?

Promoting unwanted movement. Signup and view all the answers

What characterizes the activity of neurons in the internal segment of the globus pallidus?

They are tonically active and inhibit thalamic complexes. Signup and view all the answers

Which aspect of saccadic eye movements involves caudate neurons?

Planning and executing the movement only. Signup and view all the answers

What distinguishes the direct pathway of the basal ganglia?

It promotes desired movements. Signup and view all the answers

What is the primary function of the substantia nigra pars reticulata in the oculomotor loop?

To serve an analogous function to the globus pallidus Signup and view all the answers

Which pathway allows for the suppression of competing motor programs within the basal ganglia?

Indirect pathway via the subthalamic nucleus Signup and view all the answers

How do medium spiny neurons from the putamen innervate the globus pallidus in the direct pathway?

Forming synapses within localized limited areas Signup and view all the answers

What characterizes the tonic and transient activities within the basal ganglia?

Tonic activity is background activity and transient activity is due to external stimuli Signup and view all the answers

What is the main goal of the antagonistic interaction between direct and indirect pathways in the basal ganglia?

To facilitate the selection and initiation of motor programs Signup and view all the answers

What distinguishes the afferent distribution of the indirect pathway from that of the direct pathway in the globus pallidus?

The indirect pathway has a more even distribution throughout the internal segment Signup and view all the answers

In the context of basal ganglia output loops, what does the term 'centre-surround' functional organization refer to?

The organization that demarcates inhibition and excitation between competing pathways Signup and view all the answers

What role does the globus pallidus play in the motor control functions of the basal ganglia?

It serves as a mediator for motor program selection and inhibition Signup and view all the answers

What type of dopamine receptor is expressed by medium spiny neurons in the direct pathway?

D1 receptor Signup and view all the answers

Which effect do D2 receptors have on medium spiny neurons in the indirect pathway?

Inhibit activity Signup and view all the answers

How is the modulation of behavior by dopaminergic input related to reward?

It decreases the latency of saccades with larger rewards. Signup and view all the answers

What is indicated about tremor in Parkinson's disease?

It follows a more benign course in tremor-dominant patients. Signup and view all the answers

What circuits are implicated in the pathophysiology of tremor in Parkinson’s disease?

Basal ganglia and cerebello-thalamo-cortical circuits Signup and view all the answers

In which patient demographic is tremor more commonly observed?

In approximately three out of four patients with Parkinson's disease Signup and view all the answers

Which pattern of saccades is influenced by reward in monkeys?

Shorter latencies for larger rewards Signup and view all the answers

What type of neurotransmission is primarily affected by dopamine depletion in Parkinson's disease?

Excitatory neurotransmission Signup and view all the answers

What model has been proposed to explain the pathophysiology of tremor in Parkinson's disease?

Dimmer-switch model Signup and view all the answers

Why does resting tremor stop during voluntary movements in Parkinson's disease?

Suppression of tremor by the direct pathway Signup and view all the answers

Which statement describes a characteristic of tremor-dominant Parkinson's disease?

Indicates a benign subtype of Parkinson's disease Signup and view all the answers

What happens to the expression of resting tremor as Parkinson's disease progresses?

Decreases with disease progression Signup and view all the answers

What type of neuronal degeneration occurs in Huntington's disease affecting movement control?

Degeneration of medium spiny neurons in the indirect pathway Signup and view all the answers

Which pathway is primarily responsible for the initiation of desired movements in the basal ganglia?

Direct pathway Signup and view all the answers

Which part of the brain is actively involved in suppressing unwanted movements?

Globus pallidus externus Signup and view all the answers

How does the cerebello-thalamo-cortical circuit contribute to tremor production?

By modulating output to the motor cortex Signup and view all the answers

What role do medium spiny neurons in the putamen play in the initiation of movement?

They inhibit the internal segment of globus pallidus. Signup and view all the answers

What is the primary function of neurons in the internal segment of the globus pallidus (iGB) regarding movement?

They are tonically active to inhibit the VA/VL complex of the thalamus. Signup and view all the answers

How does input from the subthalamic nucleus affect the inhibitory effect on the thalamus?

It strengthens the inhibitory effect on the thalamus. Signup and view all the answers

Which structure is analogous to globus pallidus in the function concerning the oculomotor loop?

Substantia nigra pars reticulata. Signup and view all the answers

What must occur to initiate movement involving neurons in the internal segment of the globus pallidus?

They must be inhibited. Signup and view all the answers

What is the relationship between medium spiny neurons in the putamen and the internal segment of globus pallidus (iGB)?

They inhibit the iGB to enable movement initiation. Signup and view all the answers

What type of activity do neurons in the internal segment of the globus pallidus exhibit at rest?

They are tonically active. Signup and view all the answers

What effect does the inhibition of the internal segment of globus pallidus have on thalamic activity?

It promotes an increase in excitatory thalamic activity. Signup and view all the answers

Study Notes

Function of the Basal Ganglia

Basal ganglia modulate thalamic activity through spontaneous inhibition.
Inputs to basal ganglia can increase or decrease inhibition on thalamic neurons, influencing movement initiation.
Two main pathways:
- Direct pathway: facilitates desired movement.
- Indirect pathway: inhibits unwanted movement.

Circuits of the Basal Ganglia

Medium spiny neurons in the putamen require simultaneous stimulation from cortical and nigral neurons to activate.
Putamen neurons signal limb and trunk movements; caudate neurons signal eye movements.
Anticipatory discharge from neurons can precede movement by seconds, reflecting movement selection.
Neurons of the internal segment of globus pallidus (iGP) are tonically active, inhibiting the VA/VL thalamus.
To initiate movement, iGP neurons must be inhibited by medium spiny neurons in the putamen.
Subthalamic nucleus provides excitatory input to enhance iGP inhibition on the thalamus, suppressing movement.
Substantia nigra pars reticulata functions similar to the iGP, specifically in the oculomotor loop.

Output Loops of the Basal Ganglia

Direct and indirect pathways together form a disinhibitory circuit to modulate motor program selection.
Antagonistic interaction between direct and indirect pathways results in focused motor selection.

Centre-Surround Functional Organisation

Direct and indirect pathways work antagonistically for motor program selection and initiation.
Over 100 medium spiny neurons in putamen innervate each globus pallidus cell, leading to localized synapse formation in the direct pathway.
Indirect pathway afferents from subthalamic nucleus have a broader distribution, allowing broader suppression of competing motor programs.

Modulatory Effect of Dopamine

Dopaminergic input from substantia nigra compacta influences medium spiny neuron activity.
Direct pathway neurons express D1 receptors, facilitating movement; indirect pathway neurons express D2 receptors, inhibiting activity.
Dopamine modulation may impact reward-related behaviors, affecting movement latencies in response to anticipated rewards.

Parkinson's Disease (Hypokinetic)

Tremor occurs in only about 75% of Parkinson's patients; tremor-dominant individuals may experience a less severe disease course.
Tremor is attributed to altered activity in the basal ganglia and cerebello-thalamo-cortical circuits.
The 'dimmer-switch model' explains tremor dynamics through the interplay of these circuits.

Huntington's Disease (Hyperkinetic)

Degeneration of indirect pathway medium spiny neurons in Huntington’s disease removes suppression of unwanted movements.
This leads to a hyperkinetic state where unwanted movements are not adequately inhibited.

Summary of Movement Pathways

At rest, iGP neurons inhibit VA/VL thalamus, maintaining suppressed motor activity.
Direct pathway activation initiates desired movements while the indirect pathway simultaneously suppresses unwanted movements.

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Description

Explore the intricate functions of the basal ganglia and their relationship with the thalamus. This quiz covers how spontaneous activity and selective inhibition play a role in movement control. Test your understanding of these neural circuits and their implications in motor functions.