What is meant by a second order neuron?
Second order refers to all of the spinal cord neurons that receive input from the primary afferent fibers, including interneurons and projection neurons. Second-order neurons are also located in the dorsal column nuclei; these receive input from large, non-nociceptive, primary afferent fibers that ascend to the medulla via the posterior columns. Note that many second-order neurons in the dorsal horn receive convergent input from small-diameter nociceptive and from large-diameter non-nociceptive primary afferent fibers.
