Which ONE of the following is disinhibited in the direct pathway of the basal ganglia motor loop

Question

BlackTom AI · Accepted Answer

Disinhibition of the thalamus underlies the direct pathway’s facilitation of voluntary movement.

1. Relevant knowledge points and concepts
- Basal ganglia direct pathway: cortex (motor) → striatum (putamen) → globus pallidus interna (GPi) / substantia nigra reticulata (SNr) → thalamus → cortex.
- Neurotransmitters: cortical input excites striatum with glutamate; striatum inhibits GPi/SNr with GABA; GPi/SNr tonically inhibit thalamus (GABA). Dopamine from SNc acting on D1 receptors facilitates the direct pathway.
- “Disinhibition” means reducing an inhibitory influence so a structure’s activity increases (i.e., inhibition of an inhibitor).

2. Step-by-step reasoning
- Cortical excitation increases activity in the striatum (putamen).
- Active striatal neurons using GABA inhibit GPi/SNr more strongly.
- GPi/SNr normally provide tonic inhibitory output to the thalamus. When GPi/SNr are inhibited, their inhibitory output falls.
- Reduced inhibition on the thalamus = disinhibition of the thalamus.
- Disinhibited thalamus can then increase excitatory drive back to motor cortex, facilitating movement.

3. Calculations / intermediate steps
- (No numerical calculations needed.) Logical chain: ↑cortical drive → ↑striatum activity → ↓GPi/SNr output → ↓inhibition of thalamus → ↑thalamic excitation of cortex.

4. Why the correct answer is correct
- The defining effect of the direct pathway is to remove the tonic inhibitory brake GPi/SNr exerts on the thalamus, thereby disinhibiting the thalamus and promoting cortical motor output. Thus the thalamus is the structure that becomes disinhibited.

5. Why other options are incorrect
- a. Putamen: is activated by cortex (not “disinhibited” in the pathway’s sense); it is the inhibitory nucleus initiating the chain.
- b. GPi (internal): is actually inhibited by the striatum (not disinhibited).
- c. GPe (external): is primarily part of the indirect pathway; not the main structure disinhibited in the direct pathway.
- e. Subthalamic nucleus: is involved in the indirect (excitatory) route increasing GPi output; it is not disinhibited in the direct pathway.

6. Conclusion
- Therefore the thalamus is disinhibited in the direct pathway. This confirms the correct answer: d. Thalamus.

Which ONE of the following is disinhibited in the direct pathway of the basal ganglia motor loop单项选择题

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