<prompt> Muscle rigidity due to opioids is because of their effect on:Mu receptorsKappa receptorsSigma receptorsDelta receptors  <response>: Ans. a. Mu receptors Muscle rigidity due to opioids is because of their effect on Mu receptors.All opioids green in high doses may cause muscular rigidity. It is most likely related to mu receptors in the caudate nucleus. It is more commonly seen with fentanyl. Anesthesia Review by Mitchelle Bowman Howard134Actions Ascribed to Opioid Receptorsm muk kappad delta Physical dependence morphine type Miosis Constipation m2 Analgesia supraspinalml spinal m2 Respiratory depression m2 Euphoria Sedation PM CARES Dysphoria, pscychomimetic Miosis lower ceiling Analgesia Spinal k1, supraspinal k3 Respiratory depression lower ceiling Diuresis Sedation Physical dependence nalorphine type Reduced Gl motility DMARDS Analgesia Spinal affective component of supraspinal Respiratory depression Affective behavior Reinforcing actions Reduced GI motility 