What are graded responses?

What are graded responses?

• A. Different degrees of skeletal muscle shortening
• B. Rapid contraction or tetanus
• C. A single muscle twitch
• D. No contraction

Answer: (A)

Graded responses describe how a muscle can produce different amounts of shortening and force, rather than a single on/off contraction. This happens because the nervous system can vary both how many motor units are activated (recruitment) and how frequently those units are stimulated (rate coding). When only a few motor units fire and at a low rate, the contraction is weak and the muscle shortens a little. As more motor units are recruited and firing rates increase, more fibers contract and the force—and the degree of shortening—rises. At very high stimulation rates, contractions can fuse into a sustained, stronger contraction (tetanus). So graded responses are about producing different degrees of shortening, which best fits the concept.

Graded responses describe how a muscle can produce different amounts of shortening and force, rather than a single on/off contraction. This happens because the nervous system can vary both how many motor units are activated (recruitment) and how frequently those units are stimulated (rate coding). When only a few motor units fire and at a low rate, the contraction is weak and the muscle shortens a little. As more motor units are recruited and firing rates increase, more fibers contract and the force—and the degree of shortening—rises. At very high stimulation rates, contractions can fuse into a sustained, stronger contraction (tetanus). So graded responses are about producing different degrees of shortening, which best fits the concept.