Final answer:
The motor tract carrying motor commands consists of descending nerve fibers, specifically the corticospinal tract, which includes upper and lower motor neurons that control skeletal muscle movements. The correct answer is C) Descending nerve fibers.
Step-by-step explanation:
The motor tract carrying commands or motor commands is composed of descending nerve fibers. These nerve fibers are part of the central nervous system and are responsible for carrying motor commands from the brain to the spinal cord and then to the periphery. One of the primary descending tracts is the corticospinal tract, which controls skeletal muscle movements and consists of upper motor neurons and lower motor neurons.
Upper motor neurons originate in the primary motor cortex of the frontal lobe and synapse on lower motor neurons located in the ventral horn of the spinal cord, which in turn project to the skeletal muscles. Therefore, the correct answer is C) Descending nerve fibers.