The inhibitory influence of the basal ganglia (BG) on muscle tone is stronger than the stimulatory effect due to the specific circuitry and neurotransmitters involved in the BG-thalamocortical pathway.
1. Direct and indirect pathways: The BG has two main pathways, the direct and indirect pathways, that modulate the output from the BG to the thalamus and cortex. The direct pathway facilitates movement through disinhibition, while the indirect pathway inhibits movement through hyperpolarization. The indirect pathway has an inhibitory influence on muscle tone, leading to a net inhibitory effect overall.
2. Dopamine depletion: Dysfunction or depletion of dopamine, a key neurotransmitter in the BG, is frequently associated with movement disorders like Parkinson's disease. Dopamine depletion contributes to an imbalance between the direct and indirect pathways, with the indirect pathway predominating. This imbalance leads to increased inhibition, resulting in decreased muscle tone.
3. GABAergic output: The output neurons of the BG are predominantly gamma-aminobutyric acid (GABA)ergic, which are inhibitory in nature. These GABAergic neurons exert an inhibitory control over the thalamus, reducing its excitatory output to the cortex. This inhibitory influence on the thalamus further contributes to the stronger inhibitory effect on muscle tone.
Overall, the inhibitory influence of the BG on muscle tone is stronger due to the predominance of the indirect pathway, dopamine depletion, and the inhibitory nature of GABAergic output from the BG.
why the inhibitory influence of BG is stronger than the stimulatory effect on muscle tone
1 answer