The right answer is False. (An important element missing from the definition of motor unit are motor neurons.)
A motor unit is composed of an alpha motor neuron and the muscle fibers it innervates.
Groups of motor units often work together to coordinate the contractions of a single muscle. All motor units that serve the same muscle are considered to be a group of motor units. The number of muscle fibers connected to each unit can vary: the muscles of the thigh can have up to a thousand fibers per unit, the muscles of the eyes can have only ten. In general, the number of muscle fibers involved in a motor unit is a function of the muscle's need for its refined movement: the more the muscle will need a fine movement, the less the motor unit will involve synapses with the muscle fibers.
