What is sarcomere ?

Options

A. Part between two H-lines
B. Part between two A-lines
C. Part between two I-bands
D. Part between two Z-lines

Explanation

### Step-by-Step Solution:

1. **Definition of Sarcomere**: A sarcomere is defined as the structural and functional unit of skeletal muscle fibers.

2. **Appearance of Skeletal Muscles**: Skeletal muscles are striated, meaning they have a striped appearance when viewed under a microscope. This striation is due to the arrangement of contractile proteins.

3. **Contractile Proteins**: The two main types of contractile proteins in skeletal muscle are:
- **Actin**: Known as thin filaments, which appear lighter.
- **Myosin**: Known as thick filaments, which appear darker.

4. **Banding Pattern**: The arrangement of these proteins creates alternating light and dark bands:
- The light bands are referred to as **I bands** (isotropic bands) where only actin is present.
- The dark bands are referred to as **A bands** (anisotropic bands) where myosin is present.

5. **Z Line**: The Z line is an elastic fiber that bisects the I band. It serves as an anchor point for the actin filaments.

6. **Structure of a Sarcomere**: A sarcomere is defined as the segment of muscle fiber between two consecutive Z lines.

7. **Contraction Mechanism**: During muscle contraction, the actin filaments slide over the myosin filaments, causing the sarcomere to shorten. The overlapping of the filaments increases, leading to muscle contraction.

8. **Final Definition**: Therefore, a sarcomere can be defined as the part of the muscle fiber between two Z lines, and it is the functional unit responsible for muscle contraction.