Development of corticospinal tract axons

The development of spinal axons is crucial to form, in the central nervous system, the functional circuits that are involved in the generation of locomotor patterns. The spinal axonal tracts transport the information from the motor cortex to an intricate circuit in spinal cord that allows to perform different types of motor tasks in mammals. For example, setting of fine and gross locomotor control, coordination and directing the voluntary movements and spinal reflexes are tasks dominated by spinal axon circuits. In humans, the corticospinal tract (CST), a type of axonal tract that constitutes the main motor pathway controlling voluntary movements, originates from pyramidal cells located in the primary motor and sensory cortices. CST axons begin to grow during the embryogenesis. The establishment of circuits in the final destination of the spinal cord, the refinement of CST projections to spinal gray matter, and the elimination of primitive reflexes occur during postnatal development. The three-dimensional navigation of CST axons to their final targets in the spinal cord is carefully directed by specific molecular signaling events. Alterations in CST structure can occur either during embryogenesis, with an abnormal decussation of CST or during adulthood, by mechanical trauma in the spinal cord. In both cases, the disruption of CST structure generates a pathological stage, with impairments in the locomotor activities.