What are the three components of spinal cord motor nuclei?

• A. Somatic motor axial, somatic motor distal, visceral
• B. Central, peripheral, autonomic
• C. Upper, lower, interneuronal
• D. Local circuits, projection neurons, interneurons

Answer: (A)

The spinal cord motor nuclei are organized into three functional groups that reflect their targets: two somatic motor pools for skeletal muscle and one visceral (autonomic) motor pool.

Somatic motor axial neurons innervate the trunk muscles that support posture and gross movements; these are located more medially in the ventral horn. Somatic motor distal neurons innervate limb muscles, especially the more distant, fine-control muscles; these are found more laterally in the ventral horn. Visceral motor neurons form the autonomic outflow, controlling smooth muscle, cardiac muscle, and glands; these reside in the lateral horn (intermediolateral cell column) in thoracic and upper lumbar segments and give preganglionic fibers to autonomic ganglia.

So, the three components—axial somatic motor, distal somatic motor, and visceral motor—together cover the main targets of spinal motor output: trunk, limb, and autonomic tissues.