describe the structure of striated muscle

Straited muscles:
These have striped appearance under the microscope. Therefore, they are called striated muscles. For example skeletal muscle.
Structure:

• Each skeletal muscle in the body is made of muscle bundles or fascicles. Each fascicle is held together by fascia (collagenous connective tissue layer).

• Muscle bundle: A collection of many muscle fibres

• Muscle fibre: Has sarcoplasm lined by sarcolemma (plasma member). It has the sarcoplasmic reticulum (endoplasmic reticulum) which is a storehouse for calcium ions.

• Myofibrils or myofilaments (parallel arrangement of filaments) are present inside the sarcoplasm of muscle fibre.

• Structure of Myofibril:

  • Each myofibril has alternate light and dark bands on it (striated appearance).

  • Light band: Contains the protein actin and is called the I band (Isotropic band)

  • Dark band: Contains the protein myosin and is called the A band (anisotropic band)

  • Actin: Thin filament; Myosin: Thick filament

  • Actin and myosin are arranged parallel to each other as rod-like structures.

  • Z line: An elastic fibre which bisects the I band. Portion between two Z lines represents a functional sarcomere.

  • In resting state, the thick filament partially overlaps the free ends of the thin filament.

  • H zone: The zone where the thick filaments are not overlapped by the free ends of the thin filament

  • M line: Holds the dark band at the centre; thus, it bisects the H zone.