Adrenaline increases the "alertness" of the nervous system, meaning it's ready to trigger muscle contraction. It also increases the amount of blood flow and changes the tension of the muscles, which, ...

Infectious agents can cause muscle twitching and spasms, too. The most commonly known is probably tetanus, which causes a phenomenon called lockjaw, where the neck and jaw muscles contract to the ...

Dear Dr. Gott: Once in a while, my body will "jerk" involuntarily as I fall asleep. What causes this? Does it mean I have a heart condition or other problem? Dear Reader: You appear to be describing a ...