Pools of MNs that innervate muscles of similar embryonic origin are stereotypically localized within the ventral spinal cord, known as motor columns. The medial motor column (brown) is present in the whole spinal cord and it comprises MNs that innervate the long muscles of the back and the body wall musculature. The spinal accessory column (purple) and the phrenic column (red) are found along the five first cervical segments (C1 to C5) and between C3 and C5, respectively. The preganglionic column (yellow) extends from the first thoracic segment (T1) to the second lumbar segment (L2), and between sacral segments 2 and 4 (S2 to S4) where the Onuf’s nuclei (∗) are found. MNs in the preganglionic column innervate neurons of the sympathetic ganglia. The hypaxial motor column (blue) is restricted to the thoracic spinal cord (T1 to T12). The lateral motor column (green), connected to the limbs, comprises the cervical and thoracic spinal cord (from C5 to T1) and the lumbar spinal cord (L1 to L5).