The functional unit of contractile system in a striated muscle is

Options

A. sarcomere
B. Z-band
C. cross bridges
D. nyofibril.

Explanation

**Step-by-Step Solution:**

1. **Understanding Striated Muscle**: Striated muscles, also known as skeletal muscles, are voluntary muscles found in the body that facilitate movement. They are characterized by their appearance under a microscope, showing alternating light and dark bands.

2. **Identifying Contractile Proteins**: The contraction of striated muscles is primarily due to two types of contractile proteins: actin (thin filament) and myosin (thick filament). Actin is represented in blue, while myosin is represented in pink in diagrams.

3. **Defining the Functional Unit**: The functional unit of the contractile system in striated muscles is called the sarcomere. It is defined as the segment between two Z lines in the muscle fiber.

4. **Role of the Z Line**: The Z line bisects the actin filaments and serves as an anchor point for the thin filaments. The sarcomere consists of the region between two Z lines.

5. **Mechanism of Contraction**: During muscle contraction, the actin filaments slide over the myosin filaments, leading to an overlap that shortens the sarcomere. This sliding mechanism is crucial for muscle contraction and relaxation.

6. **Conclusion**: Therefore, the functional unit of the contractile system in a striated muscle is the **sarcomere**.

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