Pain is a signal, not just a feeling
Pain begins at specialised nerve endings called nociceptors, scattered through skin, muscle, joints and the lining of organs. They are the body's alarm sensors. When tissue is damaged, stretched, burned or inflamed, these endings open ion channels that let charged particles rush in. If enough channels open, the nerve fires and sends an electrical signal up to the spinal cord and brain. We call this whole process nociception: the detection and signalling of harmful stimuli. Pain the *experience* is what the brain makes of that signal — so a drug can dampen the experience either by quieting the nerve, or by blocking the chemicals that make the nerve fire so easily.
There are two broad jobs here. A true analgesic reduces pain. An anti-inflammatory reduces the swelling, redness and heat of inflammation — and because inflammation feeds pain, anti-inflammatories are often analgesic too. Keeping these two ideas separate, then watching where they overlap, is the key to understanding the whole field.
Prostaglandins: the volume knob on pain
When a cell is injured, it releases arachidonic acid from its membrane. An enzyme called cyclo-oxygenase (COX) turns this into a family of short-lived local messengers, the prostaglandins. Prostaglandins do not usually cause pain by themselves. Instead they sensitise the nociceptor — they lower its threshold, so a touch that would normally feel like nothing now feels sore. They also widen blood vessels (redness, warmth), let fluid leak out (swelling), and act on the brain's thermostat to produce fever. One enzyme, many effects: that is why a single drug class can ease pain, swelling and fever at once.
Two places to intervene
- At the source — stop the sensitising chemicals. Block COX so fewer prostaglandins form (NSAIDs), or use corticosteroids to shut down inflammation higher upstream. This calms the nerve indirectly.
- Along the wire and at the brain — interrupt the signal itself. Local anaesthetics block the nerve's electrical conduction; opioids act on receptors in the spinal cord and brain to turn down how strongly the signal is felt and transmitted.
- Erase awareness entirely — for surgery, a general anaesthetic removes consciousness so the brain never registers the signal at all. That is the far end of the same spectrum.
Notice the ladder hidden here: from quieting one nerve ending, to blocking a whole nerve, to silencing the whole brain. Every drug in this track sits somewhere on that line. Knowing where it sits tells you what it can do — and what it cannot.