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.
Johann Gutenberg (1398-1468), inventor of the printing press. The printing press was invented in 1448 by German goldsmith Johann Gutenberg. Because it allowed books to be mass-produced and made available to the general population, the invention changed the course of history in many ways. Gutenberg was a goldsmith, metallurgist and stone cutter living in Germany.