Final answer:
At the caudal medulla, about 10% of axons in the corticospinal tract do not cross over and continue as the anterior corticospinal tract, which controls the trunk muscles, crossing over only at the spinal level to synapse with lower motor neurons.
Step-by-step explanation:
The corticospinal tract is an essential neural pathway responsible for motor control. At the caudal medulla, it undergoes a process known as the pyramidal decussation where the majority of axons cross over to the contralateral side. However, approximately 10% of the axons do not cross at this point; instead, they continue to descend ipsilaterally in the anterior corticospinal tract, which is primarily involved in controlling the muscles of the body trunk.
The anterior corticospinal tract descends through the brainstem and only crosses to the contralateral side just before it synapses with lower motor neurons in the ventral horn. This crossing at the segmental level allows for the coordination of postural muscles and bilateral movements. The lateral corticospinal tract, in contrast, contains the axons that do decussate at the pyramidal decussation and is dedicated to controlling the appendicular muscles.