Final answer:
An increase in the strength of the stimulus increases muscle tension via the recruitment of more motor units and temporal summation, where higher frequency action potentials enhance contraction strength due to overlapping muscle twitches.
Step-by-step explanation:
An increase in the strength of the stimulus will indeed cause an increase in tension development within a muscle. This effect is primarily achieved through the recruitment of more motor units. As the intensity of the stimulus increases, more motor neurons are activated, which in turn stimulates more muscle fibers to contract. In skeletal muscles, motor units have varying sizes, and their recruitment follows an orderly progression. Initially, smaller motor units with more excitable, lower-threshold neurons are activated, producing smaller contractions. With greater demand for strength, larger motor units comprising larger muscle fibers with higher-threshold neurons are recruited. This process leads to a more significant force of contraction and is an essential mechanism for adjusting the strength of muscle action based on demand.
Furthermore, it's important to understand the concept of temporal summation. When motor neurons fire action potentials at a higher frequency, such as during a stronger stimulus, individual muscle twitches can overlap, leading to increased tension due to the enhanced release of Ca++ ions and the activation of more sarcomeres. This buildup of successive muscle twitches is known as temporal summation and could result in incomplete tetanus, where quick cycles of contraction have brief relaxation phases, or complete tetanus, marked by continuous muscle contraction without any relaxation phase.
To clarify, while an increased degree of muscle stretch can influence tension development, it does so by optimizing the length-tension relationship rather than directly affecting tension due to stimulus strength. The optimal muscle length for power generation occurs when the overlap between actin and myosin filaments is greatest, allowing for maximal cross-bridge formation and force production.