Motor Neuron Columns.
Motor neuron columns contain sets of motor neurons arranged in longitudinal arrays along the rostro-caudal axis of the spinal cord, and project to distinct regions in the periphery.
The median motor column (MMC) spans across the entire rosto-caudal axis of the spinal cord, and contains motor neurons that project to axial muscles.
The lateral motor column (LMC) spans the brachial and lumbar levels of the spinal cord, and contains motor neurons that innervate the limbs. The LMCs are further split into lateral (l) and median (m) divisions, that innervate the dorsal and ventral limb muscles, respectively.
Motor neurons located within the hypaxial motor column (HMC), which spans the throracic levels, innervate body wall muscles.
The preganglionic motor column (PGC) contains visceral motor neurons located at thoracic levels, which innervate sympathetic ganglia.
The magnifications above are two transverse sections of the motor neuron column: the orange represents a section taken at the thoracic spinal cord level, while the blue represents a section taken at either the brachial, or the lumbar spinal cord levels.