Answer :
Final answer:
The sequence of activation in the cortico-basal ganglia-thalamic loop for voluntary movement follows the order of the direct pathway activation first, which enhances cortical control of movement through disinhibition of the thalamus, followed by the indirect pathway, which limits cortical control through the inhibition of the thalamus. Option b
Explanation:
The activation sequence in the cortico-basal ganglia-thalamic loop, responsible for facilitating voluntary movement, involves the interaction between direct, indirect, and hyperdirect pathways.
First, the direct pathway is activated, which consists of the cortex projecting axons to the striatum, then to the globus pallidus internal segment (GPi), and the substantia nigra pars reticulata (SNr), ultimately reaching the thalamus and looping back to the cortex. The activation of the direct pathway results in the disinhibition of the thalamus, leading to the enhancement of cortical control for movement.
Secondly, the indirect pathway is initiated, where axons project from the striatum to the globus pallidus external segment (GPe), to the subthalamic nucleus (STN), and lastly to the GPI/SNr.
The indirect pathway essentially causes or reinforces the normal inhibition of the thalamus, thus limiting the control exerted by the cortex over movement. The hyperdirect pathway, while not an answer option, plays a role in providing rapid inhibitory control to the thalamus.
Option b
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