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.
The concept of printing was first conceived and developed in China and Korea. Although the concept was conceived by the eastern nations, the first mechanized printing press was invented by a German metalworker named Johann Gutenberg in 1452.he concept of printing was first conceived and developed in China and Korea. Although the concept was conceived by the eastern nations, the first mechanized printing press was invented by a German metalworker named Johann Gutenberg in 1452.