Complex sentence: There is similar somatotopy associated with α-MNs that innervate flexor and extensor muscles: α-MNs that innervate flexors tend to be located in the dorsal portion of lamina IX; those that innervate extensors tend to be located more ventrally.
Split into simpler sentences: There is similar somatotopy associated with α-MNs that innervate flexors and extensors. In particular, α-MNs that innervate flexors tend to be located in the dorsal portion of lamina IX; those that innervate extensors tend to be located more ventrally.