Question

10) When a muscle fiber enters fatigue, which metabolite below typically does NOT significantly change in concentration? A) ATP B) P G Ca2+ D) Lactic acid E) K* 11) Which is the most accurate definition of a motor unit? A) The mimimum number of muscle fibers required to move a load B) The number of crossbridges formed in a given length of muscle fiber C) The number of muscles innervated by a single nerve D) One motor neuron and all the muscle fibers it innervates E) The maximum number of muscle fibers recruited in tetanus 12) What is the primary difference between isotonic and isometric contraction? A) How many motor units are recruited B) The stretching of serial elastic elements in the sarcomere C) The amount of shortening of sarcomere length D) Whether or not the load is moved E) The position of the troponin/tropomyosin complex on the thin filament

Answer 1

10) The correct answer is option A) ATP.

It has been observed that the metabolic pathways that regenerate ATP are turned on immediately and tightly regulated so that the net effect is that ATP concentration is only marginally reduced when muscle fiber enters fatigue. But there is a significant change in the concentrations of P_i, ADP, calcium, lactic acid and K⁺.

12) The correct answer is option D) Whether or not the load is moved.

The sarcomeres in the muscle fibers of the skeletal muscle must contract or shorten in order to move an object or load. The force generated by the shortening of the sarcomeres is known as muscle tension. Muscle tension generated by the contraction of the muscle against a load that does not move is categorized into two main types of skeletal muscle contractions namely isotonic contractions and isometric contractions.