Answer:A. The release of calcium ions causes myosin and actin to attach to each other.
The contraction of skeletal muscles takes place by induction of a nerve impulse, which produces a movement and the interaction of the filaments containing proteins named as actin and myosin. This interaction of filaments is regulated by proteins called tropomyosin and troponin present on the actin filaments. The motor nerve causes the depolarization of the muscle membrane sarcolemma. This triggers the sarcoplasmic reticulum to release calcium ions. This calcium binds to troponin and thus allows the tropomyosine strand on the actin filament to displace so that the part of the actin where myosine head needs to be attached remain uncovered. Binding of the actin myosine filament results in contraction.
Hence, the release of calcium ions causes myosin and actin to attach to each other causes muscle contraction.
The smooth, but steady, increase in muscular tension produced by increasing the number of active motor units is called a recruitment.
Muscle tension is the force produced when a muscle contracts (or when sarcomeres shorten). The two primary forms of skeletal muscle contractions, isotonic contractions and isometric contractions, are produced when a muscle contracts against a load that is not moving.
- A load is transported as the length of the muscle varies during isotonic contractions, in which the tension in the muscle remains constant (shortens). Concentric and eccentric contractions are the two varieties of isotonic contractions.
- When a muscle contracts isometrically, the angle of a skeletal joint remains the same while tension is produced in the muscle. Sarcomeres shorten and muscles tense up during isometric contractions, but the load is not moved since the force generated is insufficient to overcome the resistance provided by the load.
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Answer:
consisting of one new and one old chain of nucleotides.
is described as semi-conservative, half of the chain is part of the original DNA molecule, half is brand new.
It's called telophase in mitosis