In children with Down syndrome, lack of which process leads to slow timing of movement?

• A. Synaptogenesis
• B. Myelination
• C. Dendritic pruning
• D. Neurogenesis

Answer: (B)

Myelination controls how fast nerve impulses travel. In Down syndrome, white matter maturation can be delayed, leading to less myelin around axons. Myelin acts as insulation that enables saltatory conduction, so impulses jump between nodes of Ranvier and travel quickly. When myelination is reduced or delayed, conduction velocity slows, delaying the timing of motor commands and resulting in slower, less coordinated movements. Other brain-development processes like synaptogenesis, dendritic pruning, or neurogenesis shape connections, but the speed of movement timing hinges most on how well myelin insulates and speeds neural signaling.