Final answer:
The somatic motor pathway to the quadriceps involves upper motor neurons originating in the primary motor cortex sending signals through the corticospinal tract to lower motor neurons in the ventral horn, which then transmit the signals to the quadriceps muscle.
Step-by-step explanation:
The somatic motor pathway to the quadriceps muscle involves a sequence of neural processes that control voluntary movement. This process begins in the primary motor cortex with upper motor neurons (UMN) which send signals to the lower motor neurons (LMN) located in the ventral horn of the spinal cord. From there, these signals are transmitted through spinal nerves to the quadriceps muscles at neuromuscular junctions.
The corticospinal tract is crucial in this pathway, with most axons crossing over (decussating) in the medulla to the opposite side of the body - this decussation means that the right side of the motor cortex controls muscles on the left side of the body, and vice versa. The anterior corticospinal tract, involved in coordinating postural muscles, has bilateral axons that do not entirely cross to the opposite side. Voluntary control of muscle strength and movement relies on the activation of both the UMN and the LMN.