Biological Systems MCAT Practice Exam

What does the term "twitch" refer to in muscular physiology?

1. Maximum contraction

2. Smallest measurable muscle contraction

3. Optimal muscle length

4. Contraction without relaxation

The correct answer is: Smallest measurable muscle contraction

The term "twitch" in muscular physiology refers to the smallest measurable muscle contraction that a muscle fiber can produce in response to a single stimulus from a motor neuron. This contraction is characterized by a brief, rapid increase in tension, followed by a relaxation period as the muscle returns to its resting state. The twitch response is fundamental in understanding muscle physiology, as it provides insight into how muscles respond to stimuli and the mechanisms underlying muscle contraction. The concept of a twitch is important for distinguishing it from other types of muscle contractions. For instance, maximum contraction refers to the greatest force a muscle can generate, often involving multiple twitches summing together during sustained activity. Optimal muscle length denotes the position at which a muscle can generate maximum tension, which is distinct from a twitch itself. A contraction without relaxation may describe a situation such as tetanus, where contractions occur in rapid succession without sufficient time for the muscles to relax, but this does not define a single twitch. Thus, the correct association of a "twitch" with the smallest measurable muscle contraction accurately captures its role in muscular physiology.