Which of the following is true regarding the contractile response of skeletal muscle?
ExplanationIn isometric (same measure or length) contractions, muscle contraction increases the tension of the muscle. Isometric contraction is possible because muscles have elastic and viscous elements in series with the contractile elements, so contraction can occur without an appreciable decrease in length. In contrast, isotonic (same tension) contractions are contractions against a constant load, which decrease muscle length. Muscle fiber membrane depolarization during an action potential initiates muscle contraction via a process called excitation contraction coupling. The duration of the contractile response of skeletal muscle (muscle twitch) exceeds the duration of the action potential, but varies with muscle fiber type. Because the muscle contraction mechanism does not have a refractory period, repeated stimulation before relaxation causes greater tension development than during a single muscle twitch, a process called summation of contractions.
