List the two ways that motor neurons regulate motor units to develop force in a muscle

Recruitment: Motor neurons regulate force by recruiting additional motor units. When a muscle needs to generate more force, the nervous system activates more motor units, which consist of a motor neuron and the muscle fibers it innervates. This process is known as motor unit recruitment. By increasing the number of active motor units, the muscle can produce a greater force.

Rate Coding: Another way motor neurons regulate force is through rate coding, which involves changing the frequency of action potentials sent to the muscle fibers. When the frequency of action potentials increases, the muscle fibers contract more forcefully. This is because higher frequencies lead to a greater summation of muscle twitches, resulting in a stronger overall contraction. By adjusting the rate at which action potentials are fired, motor neurons can finely tune the force produced by the muscle.