Sarcomere refers to the protein of myofibril between?

Appeared in: BSF Staff Nurse - 2015

Explanation

A sarcomere is the fundamental unit of muscle contraction.
It is structurally defined as the portion of a myofibril that lies between two consecutive Z-discs (or Z-bands).
The Z-bands act as anchors for the thin actin filaments.
The arrangement of actin and myosin filaments within these boundaries gives skeletal and cardiac muscle their characteristic striated (striped) appearance.

Option A: The A-band (dark band) and H-zone (central part of A-band) are components within a single sarcomere, not its boundaries. The sarcomere contains these structures.
Option B: While the Z-band is one boundary of the sarcomere and the A-band is a major component, a sarcomere is not defined as the space between an A-band and a Z-band. The I-band lies between the Z-band and the A-band.
Option C: The A-band (dark band) and I-band (light band) are adjacent regions within the striated pattern of a myofibril, but they do not define the complete functional unit of a sarcomere.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Structure of a sarcomere in muscle tissue as background academic context rather than a clinical decision trigger.
Understanding the sarcomere is fundamental to comprehending how muscles generate force and movement.
Muscle hypertrophy (growth) from exercise involves adding more sarcomeres and myofibrils, increasing the muscle's contractile force.
Pathological conditions like muscular dystrophies involve defects in proteins that support the sarcomere's structure, leading to progressive muscle weakness.

How to Approach the Question

First, identify the key term in the question, which is 'Sarcomere'.
This is a factual recall question from anatomy and physiology.
Recall the definition of a sarcomere. It is the basic contractile unit of a muscle.
Visualize or remember the diagram of a myofibril with its repeating striped pattern.
The stripes are made of different bands (A, I, H) and lines (Z, M).
The sarcomere is the entire repeating unit. Recall what marks the beginning and end of this unit. The Z-lines (or Z-bands) serve as the boundaries. Therefore, a sarcomere is the region between two Z-bands.

Concept Tested & Keywords

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E6 Physiology Guyton 4SAE Part 1 p. 140-141

E6 Harper's Illustrated Biochemistry2023 (pp 26-793 of 813) pp. 604-606, 603-605

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