Which mechanism leads to nociceptive pathways being more easily triggered?

• A. Muscle fatigue
• B. Peripheral sensitization
• C. Joint laxity
• D. Central sensitization

Answer: (D)

Central sensitization is the mechanism that makes nociceptive pathways more easily triggered. After sustained or intense nociceptive input, the neurons in the spinal cord and brain become hyperexcitable. This involves changes such as NMDA receptor–mediated wind-up and glial activation, which lower the activation threshold and expand the receptive fields of nociceptive neurons. As a result, even normally non-painful or mild stimuli can provoke pain (allodynia) and pain from stimuli that would previously be only mildly painful (hyperalgesia). This CNS amplification explains why pain can become amplified and widespread after ongoing injury or inflammation. Peripheral sensitization, by contrast, lowers the threshold at the site of injury, and joint laxity or muscle fatigue relate more to mechanical or tissue factors rather than increasing CNS responsiveness.