Final answer:
Descending tracts indeed carry motor impulses from the cerebral cortex to the spinal cord through the corticobulbar and corticospinal tracts, which control voluntary muscle movement in different parts of the body.
Step-by-step explanation:
The motor system is hierarchically structured, with the primary motor cortex (located in the frontal lobe of the cerebral cortex) at the highest level. The motor signals, which initiate voluntary muscle movements, travel through two major ascendent pathways from the brain to the spinal cord—the corticobulbar tract and the corticospinal tract. The corticobulbar tract projects to motor nuclei of cranial nerves and is involved with control of head and face movements.
The corticospinal tract primarily carries motor impulses to the rest of the body, with its axons crossing over, or decussating, at the level of the brain stem, enabling the right side of the motor cortex to control muscles on the left side of the body, and vice versa. These descending pathways communicate with lower motor neurons located in the ventral horn of the spinal cord or within the cranial nerve nuclei in the brain stem to ultimately control skeletal musculature. The Betz cells, which are large cortical neurons, are important components of these tracts and are found in the primary motor cortex.