Pain begins when specialized nerve endings detect tissue damage, heat, pressure, or chemical signals from inflammation. These signals travel through peripheral nerves to the spinal cord and then to the brain, where they become the conscious experience of pain. Painkillers and anesthetics matter because they can reduce suffering, allow healing, and make surgery possible.
Different drugs work at different points along the pain pathway, from the injury site to the brain.
Key Facts
- NSAIDs such as ibuprofen and aspirin inhibit COX enzymes, which lowers prostaglandin production and reduces inflammation and pain.
- Prostaglandins sensitize pain receptors, so less prostaglandin usually means fewer pain signals start at the injury site.
- Local anesthetics such as lidocaine block voltage-gated sodium channels, so action potentials cannot travel along nearby nerves.
- Opioids bind mu opioid receptors in the brain, spinal cord, and other tissues, reducing pain signaling and changing pain perception.
- General anesthetics often enhance GABA signaling, which increases inhibition in the brain and can produce unconsciousness.
- A simplified nerve signal rule is stimulus above threshold → action potential → neurotransmitter release → signal passed to the next cell.
Vocabulary
- Nociceptor
- A sensory nerve ending that detects potentially harmful stimuli such as heat, pressure, injury, or inflammatory chemicals.
- COX enzyme
- An enzyme that helps make prostaglandins, which are chemicals involved in inflammation, fever, and pain sensitivity.
- Sodium channel
- A protein pore in a nerve cell membrane that lets sodium ions enter and helps generate an action potential.
- Mu opioid receptor
- A receptor that opioids can activate to reduce pain signaling and also produce effects such as euphoria and dependence risk.
- GABA
- The main inhibitory neurotransmitter in the brain, which lowers the activity of many neurons.
Common Mistakes to Avoid
- Thinking all painkillers work the same way. This is wrong because NSAIDs, acetaminophen, opioids, local anesthetics, and general anesthetics act on different molecules and different parts of the nervous system.
- Assuming local anesthetics make the brain unconscious. This is wrong because local anesthetics mainly block nerve signal conduction near where they are applied while the person can remain awake.
- Using more medicine than directed because pain is strong. This is dangerous because higher doses can cause serious harm, such as liver damage from acetaminophen or breathing problems from opioids.
- Confusing pain relief with healing. A drug may reduce the pain signal, but the injured tissue may still need rest, treatment, or time to repair.
Practice Questions
- 1 A pain signal travels from an injured finger to the spinal cord at 50 m/s over a distance of 1.2 m. How long does the signal take to reach the spinal cord?
- 2 A patient is told to take 400 mg of ibuprofen every 6 hours, with a maximum of 1200 mg per day. If the patient takes one dose at 8 a.m., 2 p.m., and 8 p.m., what total dose is taken that day, and is it within the limit?
- 3 A dentist injects lidocaine near a tooth before drilling. Explain why the tooth area becomes numb even though the patient remains awake and can still hear and see.