CBSE Class 12-science Answered

When tissue is injured, there follows a rapid release of ‘messenger’ chemicals that stimulate the nerve endings. Electrical impulses are relayed through the nerves to the spinal column and to the brain, which registers the sensation of pain. It usually, but not always, also directs our attention to the site where the damaged tissue initiated the pain message.

Aspirin acts at the site of damaged tissue to block the start of the nerve signal to the brain, the mechanism by which we experience pain. It does this by inhibiting the formation of prostaglandin which is the active agent responsible for the sensitization of the nerve endings. Prostaglandins (there are several related types) are responsible for a lot of physiological events in addition to the start of the pain signal at the nerve ending. For example, they are responsible for inflammation, fever and the clotting of platelets in the blood, so it is easy to see why aspirin is such a useful drug.