Which structure contains sensory fibers that transmit the sensation of light touch?

• A. Spinothalamic tract
• B. Posterior column
• C. Spinothalamic tract and posterior column
• D. Proprioception

Answer: (C)

Light touch is conveyed through two parallel pathways in the somatosensory system. The dorsal column–medial lemniscus pathway carries discriminative, finely detailed touch (and also vibration and proprioception), while the anterior (ventral) part of the spinothalamic tract carries crude or light touch and pressure. Because light touch can involve both a basic, less precise sensation and more detailed discrimination, fibers for light touch are found in both the spinothalamic tract and the posterior column. Proprioception is a separate sense of body position and, while it travels with the posterior column, it is not the light touch sensation itself. So the structures that contain fibers for light touch include both pathways together.