Final answer:
The medullary reticular nuclei are the group that overcomes reflexive postural maintenance for controlled movements, being part of the extrapyramidal system. The vestibulospinal and reticulospinal tracts also play essential roles in balancing and posture in the extrapyramidal system.
Step-by-step explanation:
The set of reticular nuclei that acts to overcome reflexive postural maintenance during controlled purposeful movements are the medullary reticular nuclei. This group of nuclei is part of the extrapyramidal system that includes projections from the brain stem and higher centers, which greatly influence movement, mostly to maintain balance and posture, as well as to maintain muscle tone. One of the key pathways in this system is the reticulospinal tract, which integrates motor commands for postural adjustments.
Additionally, the vestibulospinal tract is specifically involved in incorporating equilibrium sensations with motor commands to aid in posture and movement, demonstrating the significant role of the vestibular system in similar functions. Neurons in the vestibular nuclei project to several brain structures, including the reticular formation and the spinal cord, to help regulate posture and balance. Moreover, the vestibular nuclei contribute to the vestibulo-ocular reflex (VOR), adjusting eye movements to compensate for head movements, thereby stabilizing the retinal image.