What is sarcoplasmic reticulum ? What is its function ?

Explanation

### Step-by-Step Solution:

1. **Definition of Sarcoplasmic Reticulum**:
- The sarcoplasmic reticulum (SR) is a specialized type of smooth endoplasmic reticulum found in muscle fibers. It forms a network around the myofibrils (the contractile elements of muscle cells).

2. **Structure**:
- Under an electron microscope, the sarcoplasmic reticulum appears as a network of tubules and sacs. It is composed of two main types of bands: the A-band and the I-band, which are associated with the actin and myosin filaments responsible for muscle contraction.

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