Ivy Tech APHY 101 – Muscle System Practice Test 2026 - Free Muscle System Practice Questions and Study Guide

The sarcomere is the smallest contractile unit of muscle, defined as the segment extending from one Z disc to the next. This unit houses the precise arrangement of actin (thin) and myosin (thick) filaments that slide past each other during contraction, shortening the length of the sarcomere and, in turn, the muscle fiber. Because contraction occurs by the shortening of each sarcomere in series along a myofibril, the entire muscle shortens when many sarcomeres shorten together. A myofibril, by contrast, is a bundle of many sarcomeres in sequence; thick filaments are the myosin structures inside the sarcomere; and endomysium is the connective tissue surrounding a single muscle fiber, not a contractile unit.