The tetanus is a disease caused by the bacterium Clostridium tetani. The Clostridium tetani is a normal inhabitant of the soil and can easily contaminate dirty wounds, especially those due to farm practices. In the body, these bacteria produce a toxin called tetanospasmin. The toxin enters the central nervous system which is the brain and spinal cord where it blocks the mechanisms that inhibit motor neurons from firing when a muscle is relaxed. With this inhibition removed, the neurons fire repeatedly and continually stimulates the muscle, causing painful and increasingly stronger muscle spasms. The masseter or jaw muscles are often the first muscles involved, and it is the spasm of these muscles that gives rise to tetanus' common name lockjaw, also called trismus. The muscles of the face, neck, back, and proximal limbs are also commonly affected. The contraction of the facial musculature leads to a characteristic facial expression with a teeth-baring grin and raised eyebrows. Contraction of the back muscles may cause the back to arch posteriorly.
Galileo Galilei discovered io on January 8th, 1610 and the discovery, along with the three other Jovian moons Europa, Ganymede and Callisto, were the first moons discovered that were orbiting a planet other than Earth
