Question

In order for a skeletal muscle fiber to contract, what 4 things must happen?

Answer 1

A skeletal muscle fiber must be stimulated to fire an action potential, after which the release of calcium ions triggers the sliding filament model of muscle contraction and the myosin heads bind to actin and pull the actin filaments to result in sarcomere shortening and muscle contraction.

Step-by-step explanation:

For a skeletal muscle fiber to contract, four things must happen:

1. The muscle fiber must be stimulated to fire an action potential (excitation).
2. The action potential triggers the release of calcium ions (Ca++) from the sarcoplasmic reticulum (SR), which is then used in the contraction process (excitation-contraction coupling).
3. The calcium ions interact with the shielding proteins, troponin and tropomyosin complex, which move aside to expose the actin-binding sites for attachment by myosin heads (interaction of calcium ions with shielding proteins).
4. The myosin heads bind to actin, forming cross-bridges, and then pull the actin filaments toward the center, resulting in sarcomere shortening and muscle contraction (sliding filament model of muscle contraction).