Final answer:
Muscle tension during fused tetanus is lost primarily due to muscle fatigue, where ATP and calcium ion concentrations decline, inhibiting cross-bridge cycling necessary for muscle contractions. Treppe contributes to temporary increases in efficiency, but sustained tension cannot be maintained indefinitely. In pathology, toxins such as Tetanospasmin might provoke sustained spasms, without the normal relaxation phase, leading to generalized tetanus.
Step-by-step explanation:
In the context of muscle physiology, fused tetanus occurs when muscle contractions become continuous due to high-frequency stimulation that eliminates the relaxation phase between contractions. However, during fused tetanus, muscles may eventually lose tension due to muscle fatigue. This fatigue is typically because the continuous demand for ATP cannot be met, and there is a decline in calcium ion concentration within the sarcoplasm as the muscle's energy systems become exhausted. Additionally, cross-bridge cycling, which is critical for muscle contraction, cannot continue indefinitely without sufficient ATP, and without calcium, the myosin heads cannot effectively bind to the actin filaments, leading to a decrease in muscle tension.
Furthermore, the phenomenon of treppe demonstrates that a muscle will contract more efficiently after it has been contracting for a period, due to more available calcium in the sarcoplasm and increased enzyme efficiency. This efficiency increase, however, is only temporary, and over time the muscle will fatigue and be unable to sustain the same level of tension.
In severe pathological cases, substances like the Tetanospasmin toxin in generalized tetanus can prevent the release of neurotransmitters responsible for muscle relaxation, resulting in sustained, uncontrollable muscle spasms.