Answer:
every muscle cell of the motor unit is stimulated to contract.
Step-by-step explanation:
Stimulus in biology can be defined as an obvious change in either the chemical or physical structure of an organism' environment (either external or internal). Thus, all living organisms (both animals and plants) respond to changes in their environment and consequently, an appropriate response or reaction is made. Also, stimulus arising from within the organism is known as internal stimulus while those from its environment are known as the external stimulus.
In organisms, the specialized cells that detect stimulus are generally known as sensory receptors while a group of these receptors is referred to as sense organ. Therefore, the senses are necessary for behavior because stimuli must be sensed in order to respond.
Stimulus control can be defined as a phenomenon that arises when a living organism responds or behaves in the presence of a stimulus and in another way in the absence of a stimulus.
For example, opening the door of a microwave oven as soon as its timer beeps.
Example II; When your body touches a hot object, you quickly move away and feel some pain subsequently.
Action potentials generates the nerve impulse in a motor neuron.
When an action potential is generated within a motor neuron, every muscle cell of the motor unit is stimulated to contract.