Basal Ganglia Pathways

Origin of the Motor Loop

• The motor loop originates from the cerebral cortex, specifically areas involved in motor control.

Role of the Direct Pathway

• The direct pathway facilitates selected motor actions by providing excitatory inputs to the motor thalamus, increasing motor activity.

Effect of Cortical Activation on Putamen Neurons

• Cortical activation leads to excitation of putamen neurons, enhancing their activity in the motor loop.

Neurons in the Internal Segment of the Globus Pallidus at Rest

• These neurons tonically inhibit the thalamus, preventing unwanted motor activity when at rest.

Inhibition of GPi Neurons by Putamen Neurons

• When putamen neurons inhibit GPi neurons, it reduces inhibitory output to the thalamus, allowing increased movement.

Effect of VLo Activity on the Supplementary Motor Area (SMA)

• VLo activity enhances the excitability of the SMA, promoting motor planning and execution.

Function of Circuit Involving VLo and SMA

• This circuit plays a crucial role in coordinating and planning motor actions, linking higher-order cognitive functions with motor control.

Antagonism of the Direct Pathway

• The indirect pathway tends to antagonize motor functions of the direct pathway, competing for the same motor outputs.

Nucleus Excited by Cortical Axons

• The subthalamic nucleus is excited by cortical axons, which project to and excite GPi neurons, influencing movement.

Activation of the Indirect Pathway by Cortex

• Activation of the indirect pathway leads to increased inhibition of the thalamus, thereby reducing motor output.

Role of Direct Pathway in Action Selection

• It assists in the selection of desired motor actions, helping to streamline movement execution.

Structure Inhibited by GPe

• The Globus Pallidus externus (GPe) inhibits neurons in both the GPi and the subthalamic nucleus, modulating their activity.

Role of Indirect Pathway for Competing Motor Programs

• It functions to suppress competing motor programs that may interfere with the execution of desired movements.

Pathway that Facilitates Thalamus

• The direct pathway through the basal ganglia facilitates the thalamus, promoting informational flow relevant to movement.

Unique Feature of the Indirect Pathway

• The indirect pathway's unique feature is simultaneous suppression of unwanted motor activities while enhancing the inhibition of the thalamus.

Antagonism of Direct Pathway by Other Functions

• The indirect pathway's activity antagonizes the facilitation of motor functions provided by the direct pathway.

Neurons Excited by Subthalamic Nucleus

• The subthalamic nucleus excites neurons in the GPi, contributing to movement regulation.

Direct Pathway Activation and Facilitation

• Activation of the direct pathway by cortical signals tends to facilitate voluntary movements.

Indirect Pathway Suppression

• The indirect pathway simultaneously suppresses motor activities that are not selected for execution.

Positive-Feedback Loop Function

• The positive-feedback loop within the circuit enhances specific motor outputs and reinforces selected motor actions, contributing to efficient motor control.

Test your knowledge of the direct and indirect pathways through the basal ganglia with this quiz. Explore the motor loop originating from the cortex and the excitatory and inhibitory connections within the basal ganglia.