Such a contraction is called a twitch. Thus, each motor unit is either relaxed or each presynaptic action potential causes an action potential in all of the muscle fibers of the motor unit, causing them all to contract at once.In the whole muscle, contractions of different strengths necessarily are created by activating different numbers of motor units.hus, each motor unit is either relaxed or each presynaptic action potential causes an action potential in all of the muscle fibers of the motor unit, causing them all to contract at once. In the whole muscle, contractions of different strengths necessarily are created by activating different numbers of motor units.
Johannes Gutenberg of Mainz, Germany is acknowledged as the first to invent a metal movable-type printing system in Europe, the printing press.
According to most historians, the printing press was invented by Gutenberg, in Mainz, in the Holy Roman Empire (Germany) in 1441, or about that time.irst printing press was invented in China by Bi Sheng in 1040 by  movable terracotta, before popularised in Europe by Johnnes  Guttenburg in 1443.