What term defines the lateral boundaries of the sarcomere in muscle fibers?

The lateral boundaries of the sarcomere in muscle fibers are defined by the Z line. The Z line serves as an anchoring point for actin filaments and marks the start and end of a sarcomere, which is the basic contractile unit of muscle tissue. Each sarcomere is bounded on either side by a Z line, and as muscles contract, the actin filaments slide past the myosin filaments, causing the sarcomeres to shorten while the Z lines get closer together. This arrangement creates a striated appearance in skeletal muscle due to the alternating bands of actin and myosin fibers.

It is important to note that while the terms "Z disk" and "Z line" are often used interchangeably, the more specific scientific terminology typically refers to the Z line. The M line is different, as it is located in the center of the sarcomere and serves as a point of attachment for myosin filaments, while the A band refers to the region that includes the length of the thick filaments and the overlapping area with thin filaments.