How can some pain relievers work to reduce pain signals at the synapse?

Opioid pain killers block synaptic transmission of nerve impulses by binding to opioid receptors.

Explanation:

Different types of pain medication have different mechanisms of action. These pain medications are broadly classified as: Non-opioid pain killers that include aspirin and ibuprofen. These work by inhibiting the enzymes responses for producing the pain signals at the site of injury or source of pain. These enzymes, known as COX-1 and COX-2 produce a chemical called prostaglandin. This hormone transmits the pain signals to the nervous system. Opioid pain killers, such as codeine, morphine and oxycodone, physically block the synaptic transmission of the pain signal. They bind to receptors known as opioid receptors. Opioid receptors are G-protein coupled receptors (GPCR). In cell signaling, GPCRs are receptors that activate/inhibit signaling pathways through activation/inhibition of adenylyl cyclase, an enzyme that producing cAMP, a second messenger that regulates the K + and Ca+2 channels responsible for nerve impulse transmission. Opioid pain killers inhibit adenylyl cyclase consequently reducing cAMP production. This blocks Ca+2 channels and opens K + channels in the neurons, thereby reducing neuron excitability and the release of neurotransmitters.

3. Adjuvant pain killers are used to treat neuropathic pain i. e. pain due to injury of the nervous system.