Question

When does summation occur in muscle cells?

1) When action potentials are added to produce a greater force stimulating contraction
2) During relaxation phase
3) During repolarization
4) When calcium ions are released into the cytoplasm

Answer 1

Summation in muscle cells occurs when action potentials are added together, resulting in a stronger muscle contraction due to release of more calcium ions into the cytoplasm, which then activate more sarcomeres. The correct answer to the question is option 1.

Step-by-step explanation:

Summation in muscle cells occurs when action potentials are added to produce a greater force stimulating contraction. This process, known as wave summation, involves the summing of the excitation-contraction coupling effects of isuccessive motor neuron signaling. When a second stimulus is provided to muscle fibers that are still contracting from the first stimulus, it triggers the release of more calcium ions (Ca++) into the cytoplasm. These additional calcium ions become available to activate more sarcomeres, resulting in a stronger and greater contraction of the motor unit.

The process of summation allows muscles to produce responses that vary from weak to very strong contractions, depending on the frequency and intensity of motor neuron signals. At a high enough stimulus frequency, there may be no relaxation phase, leading to what's called complete tetanus, where contractions become continuous and produce maximal tension.

Therefore, the correct option for when summation occurs in muscle cells is: 1) When action potentials are added to produce a greater force stimulating contraction.