How do opiates and narcotics affectthe nervous system?

The nervous system produces its own version of morphine. (endorphins, dynophins, enkephalin, etc.) These intrinsic opiates act at different opiate receptors(mu, beta, and kappa receptors). Extrinsic opiates, like morphine, also fit into these receptors and result in the same effects as intrinsic body opiates.(morphine's pain relieving effects are mostly due to interaction with the mu opiate receptor). Hope that helps