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.
Overview. Johannes Gutenberg's invention of the printing press is widely thought of as the origin of mass communication-- it marked Western culture's first viable method of disseminating ideas and information from a single source to a large and far-ranging audience.ntil the 19th century Gutenberg's print technology had not changed dramatically. In the early 1800's the development of continuous rolls of paper, a steam-powered press and a way to use iron instead of wood for building presses all added to the efficiency of printing.