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Human neurons are so small that they require a microscope in order to be seen. However, some neurons can be up to 3 feet long, such as those that extend from the spinal cord to the toes.
It is believed that the Incas used anesthesia. Evidence supports the theory that shamans chewed cocoa leaves and drilled holes into the heads of patients (letting evil spirits escape), spitting into the wounds they made. The mixture of cocaine, saliva, and resin numbed the site enough to allow hours of drilling.
Addicts to opiates often avoid treatment because they are afraid of withdrawal. Though unpleasant, with proper management, withdrawal is rarely fatal and passes relatively quickly.
When blood is exposed to air, it clots. Heparin allows the blood to come in direct contact with air without clotting.
Pregnant women usually experience a heightened sense of smell beginning late in the first trimester. Some experts call this the body's way of protecting a pregnant woman from foods that are unsafe for the fetus.