Question

4 multiple choice 1 point
in order for a muscle contraction to occur, cross-bridges must form between which one of the following structures within a muscle cell?
calcium and tropomyosin
acetylcholine and muscle cell receptors
actin and myosin
the plasma membrane and the sarcoplasmic reticulum
troponin and tropomyosin

5 multiple choice 1 point
as part of your fitness training, you do bicep curls lifting two 10-lb weights. the muscle contractions enabling these movements are
tendon-mediated contractions.
tetanic contractions.
isometric contractions.
isotonic contractions.
treatment-mediated contractions.

Explanation:

For question 4: Muscle contraction relies on the sliding filament theory, where cross-bridges form between the thin actin filaments and thick myosin filaments to pull the filaments past each other. The other options involve regulatory molecules, signaling steps, or cellular structures that support contraction but do not form the cross-bridges themselves.
For question 5: Isotonic contractions involve muscle shortening while maintaining a constant tension, which occurs during bicep curls as the muscle lifts the fixed weight and changes length. Isometric contractions involve no length change, tetanic contractions are sustained, and the other options are not standard contraction types for this movement.

Answer:

1. actin and myosin
2. isotonic contractions