Question

More cytosolic Ca2+ leads to more exposed myosin binding sites, leads to more cross-bridges forming, leads to higher contractile force of that particular fiber:

A) Positive feedback loop

B) Negative feedback loop

C) Feedforward regulation

D) Homeostatic regulation

Answer 1

The increase in cytosolic Ca2+ which leads to more myosin binding and higher contractile force is an example of a positive feedback loop. It is part of the excitation-contraction coupling mechanism in muscle fibers, relying on calcium ion release from the sarcoplasmic reticulum.

Step-by-step explanation:

The process described as increasing cytosolic Ca2+ leading to more exposed myosin binding sites, more cross-bridges forming, and as a result, a higher contractile force of a muscle fiber, aligns with the concept of positive feedback loop in physiological systems. In this loop, the initial stimulus (more Ca2+ in the cytosol) is amplified to produce a larger effect (increased muscle contraction), which in turn promotes more of the stimulus (further Ca2+ release).

This mechanism is part of excitation-contraction coupling in muscle fibers, where the sarcolemma must be excited to trigger an action potential which is then coupled to muscle contraction via calcium ions (Ca2+) release from the sarcoplasmic reticulum (SR). The released Ca2+ ions interact with troponin and tropomyosin on the actin filaments, leading to the formation of cross-bridges between actin and myosin, ultimately resulting in muscle fiber contraction.