Basal Ganglia Direct Pathway

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Questions and Answers

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

  • To suppress the subthalamic nucleus (STN)
  • To facilitate movement by disinhibiting the thalamus (correct)
  • To excite the globus pallidus internus (GPi)
  • To inhibit the thalamus and reduce motor output

Which neurotransmitter does the striatum release to inhibit the globus pallidus internus (GPi) in the direct pathway?

  • Glutamate
  • Acetylcholine
  • Dopamine
  • GABA (correct)

The indirect pathway increases motor activity by exciting the thalamus.

False (B)

Which structure does the globus pallidus externus (GPe) inhibit in the indirect pathway?

<p>Subthalamic nucleus (STN) (B)</p> Signup and view all the answers

What is the net effect of the direct pathway on motor activity?

<p>increased</p> Signup and view all the answers

The direct pathway facilitates movement by ______ the thalamus.

<p>disinhibiting</p> Signup and view all the answers

Match each structure with its correct role in the basal ganglia pathways:

<p>Striatum = Receives excitatory input from the cerebral cortex Globus Pallidus Internus (GPi) = Sends inhibitory signals to the thalamus Subthalamic Nucleus (STN) = Excites the GPi in the indirect pathway Thalamus = Sends excitatory signals to the motor cortex</p> Signup and view all the answers

If the indirect pathway is damaged, what is the likely outcome?

<p>Increased motor activity (D)</p> Signup and view all the answers

Flashcards

Basal Ganglia

Subcortical nuclei regulating motor control, motor learning & other functions.

Direct Pathway

Facilitates movement by disinhibiting the thalamus, increasing motor output.

Indirect Pathway

Suppresses movement by increasing inhibitory output to the thalamus.

Cerebral Cortex Input

Excitatory input to the striatum; starts both direct and indirect pathways.

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Striatum (Direct)

Inhibits the GPi in the direct pathway, disinhibiting the thalamus.

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Striatum (Indirect)

Inhibits the GPe in the indirect pathway, leading to increased GPi activity.

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Globus Pallidus Externus (GPe)

Inhibited by the striatum. When released, it excites the STN.

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Globus Pallidus Internus (GPi)

Receives excitatory input from STN, inhibits thalamus, reducing motor output.

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Study Notes

  • Basal ganglia are a group of subcortical nuclei regulating motor control, motor learning, and other functions.
  • Movement is regulated by the direct and indirect pathways through the basal ganglia.
  • These pathways modulate motor output by influencing the thalamocortical circuits.
  • The thalamocortical circuits affect the primary motor cortex and voluntary muscle movements.

Direct Pathway (Facilitatory Pathway)

  • The direct pathway facilitates movement by disinhibiting the thalamus.
  • This disinhibition increases motor output.
  • The cerebral cortex sends excitatory input (glutamate) to the striatum (caudate and putamen).
  • The striatum releases GABA to inhibit the globus pallidus internus (GPi).
  • GPi normally exerts an inhibitory effect on the thalamus.
  • Disinhibition of the thalamus allows it to send excitatory signals back to the motor cortex which facilitates voluntary movement.
  • The net effect of the direct pathway is increased motor activity.
  • The thalamus "excites" the motor cortex, leading to increased movement.

Indirect Pathway (Inhibitory Pathway)

  • The indirect pathway suppresses movement by increasing the inhibitory output to the thalamus.
  • The increased inhibition decreases motor output.
  • The cerebral cortex sends excitatory input to the striatum.
  • The striatum inhibits the globe pallidus externus (GPe).
  • Inhibition of the GPe releases its hold on the subthalamic nucleus (STN).
  • The subthalamic nucleus (STN) becomes excited and sends excitatory signals (glutamate) to the globus pallidus internus (GPi).
  • The excited GPi sends more inhibitory signals to the thalamus, suppressing motor output.
  • The net effect of the indirect pathway is reduced motor activity.
  • This is because it increases inhibition of the thalamus.
  • The increased inhibition reduces excitatory signals to the motor cortex and thus suppresses movement.

Balanced Interaction Between the Pathways

  • The direct pathway facilitates movement, while the indirect pathway suppresses it.
  • Dysfunction in these pathways can result in movement disorders.
  • In Parkinson's Disease, degeneration of dopaminergic neurons in the substantia nigra causes a reduction of dopamine input into the striatum.
  • The reduction of dopamine in Parkinson's causes increased indirect pathway activity with over-inhibition of the thalamus.
  • Parkinson's also causes decreased direct pathway activity with reduced disinhibition of the thalamus.
  • The combined activity contributes to bradykinesia, rigidity, and tremor.
  • Huntington's Disease is characterized by degeneration of the striatum, especially the indirect pathway.
  • Degeneration of the striatum leads to less inhibition of the thalamus.
  • Huntington's results in hyperkinetic movements like chorea.

Summary of the Pathways

  • Direct pathway facilitates movement by disinhibiting the thalamus.
  • Indirect pathway inhibits movement by increasing thalamic inhibition.
  • Both pathways work together to fine-tune motor control; dysfunction leads to various movement disorders.

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