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.
Johannes Gutenberg was a German blacksmith known for inventing the mechanical movable type printing press. His printing press has been widely considered the most important invention of the modern era because it profoundly impacted the transmission of knowledge. Invented around 1439, Gutenberg's movable type printing press initiated nothing less than a revolution in print technology.