Ultrastructure of a Striated Muscle myofibril

mt_06. Ultrastructure of a striated muscle myofibril
(transmission electron microscopy, х10000)

1. General characteristics

Myofibrils are main striated muscle organelles:
- have a characteristic banding pattern, referred to as striations, where repeating light I bands (isotropic) and dark A bands(anisotropic) can be observed;
  - I bands are composed of thin myofilaments which include actin;
  - A bands are formed by thick myofilaments that include myosin;
  - close observation of the A band shows the presence of a lighter zone in its center, the H band; the M line bisects the H band;
  - A bands are composed mainly of thick filaments in addition to portions of overlapping thin filaments;
- the myofibrils consist of sarcomeres delimited by two very dark colored bands called Z discs or Z lines.

2. Draw and point out:

I - a myofibril;