Upper motor neurons (UMNs) originate in the cerebral cortex, including the primary motor cortex, premotor cortex, and supplementary motor areas, as well as in brainstem motor centres, and are responsible for initiating and modulating voluntary movement. Their axons descend through the central nervous system and synapse directly or indirectly with lower motor neurons (LMNs) in the spinal cord. LMNs are located in the brainstem and spinal cord and transmit motor commands to skeletal muscles to produce movement. LMNs also receive input from sensory neurons and interneurons and contribute to reflex pathways.
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