Final answer:
The direct pathway of cortical motor signal transmission involves the corticobulbar tract and the corticospinal tract. Motor commands from the primary motor cortex are sent down these pathways to activate lower motor neurons in the brain stem or spinal cord.
Step-by-step explanation:
The direct pathway of cortical motor signal transmission consists of two descending pathways: the corticobulbar tract and the corticospinal tract. Betz cells in the primary motor cortex send motor commands down these pathways to activate lower motor neurons in the brain stem or spinal cord. The axons of the corticobulbar tract project ipsilaterally to the motor nucleus on the same side of the nervous system, while the axons of the corticospinal tract largely cross the midline of the brain stem or spinal cord and synapse on the opposite side of the body.