16. The criteria to classify a neuron as a nociceptor include (A) The presence or absence of axon myelination, cell size, and/or cell content (e.g., peptide or ion channel) as well as central termination pattern. (B) Sensory neurons commonly identified as nociceptors are those with unmyelinated (C-fiber) axons, small cell body diameters (＜20 or 25 μm), that terminate in the superficial layers of the spinal cord dorsal horn. (C) The presence or absence of certain markers (e.g., the tetrodotoxin (TTX)-resistant sodium channel NaV1.8, the transient receptor potential vanilloid receptor TRPV1) have been used to identify subsets of nociceptors. stimuli, such as during prolonged application of opioids or on abrupt withdrawal of opioids.. (D) More recently, with the ability to analyze many genes expressed in a single cell, patterns of gene expression have been used to further define subpopulations of nociceptors. (E) All of the above.