Final answer:
Increasing the frequency of stimulation to a skeletal muscle leads to wave summation and potentially to incomplete or complete tetanus, which results in greater muscle tension due to increased cross-bridge formation.
Step-by-step explanation:
When the frequency of stimulation to a skeletal muscle is increased to the point where the muscle fibers do not fully relax between stimuli, the phenomenon known as wave summation occurs. This leads to an increase in muscle tension with each subsequent stimulus. If the frequency continues to increase, this can lead to incomplete tetanus, where the muscle fibers exhibit quick cycles of contraction with very short relaxation phases. If the frequency is raised even further, it can result in complete tetanus, where the contractions become continuous due to the lack of any relaxation phase.
The increase in muscle force is due to the accumulation of calcium ions in the sarcoplasm, which come from repeated stimulation before the muscle can relax. This allows more cross-bridges to form between actin and myosin, resulting in greater muscle tension. Thus, the frequency of motor neuron signaling plays a critical role in regulating the gradation of skeletal muscle force in response to the demands placed upon the muscle.