After the cerebellum receives proprioceptive information from muscles carrying out a voluntary movement, it sends corrective feedback to the upper motor neurons in the cerebral cortex, brainstem, and spinal cord through its projections1. The primary function of the cerebellum is to detect the difference or “motor error” between an intended movement and the actual movement and reduce the error through its projections to the upper motor neurons1.
So, the correct answer would be 1. Primary motor cortex and cerebral nuclei.