The segment of myofibril that is called a sarcomere runs from

The correct answer is one Z line to the next Z line

Concept:

• A sarcomere is the functional and structural unit of a myofibril in skeletal and cardiac muscle cells. It is responsible for muscle contraction and gives the muscle its striated appearance.
• The sarcomere is defined as the region between two successive Z lines (or Z discs). Z lines act as boundaries of the sarcomere.
• Each sarcomere contains an arrangement of actin (thin filaments) and myosin (thick filaments) that overlap and interact during muscle contraction.

Key Points Related to the Correct Answer:

• The Z line is a structure composed of proteins that anchors the thin filaments (actin) and marks the boundary of a sarcomere.
• The sarcomere includes distinct regions:
  • I band: The lighter region on either side of the Z line, containing only thin filaments.
  • A band: The darker region that contains the entire length of thick filaments and overlapping thin filaments.
  • H zone: A central lighter region within the A band where only thick filaments are present (no overlap with thin filaments).
• The arrangement of sarcomeres in a myofibril gives the muscle its striated appearance under a microscope.
• During muscle contraction, the sarcomere shortens as the actin and myosin filaments slide past each other, but the length of the filaments themselves does not change.