Changes

*Muscle "fiber" means a single cell, which are multi-nucleate, and known as '''syncitia'''

*Muscle "fiber" means a single cell, which are multi-nucleate, and known as '''syncitia'''

*Within each fiber are groups of parallel, longitudinal myofibrils

*Within each fiber are groups of parallel, longitudinal myofibrils

**Myofibrils are arranged as '''sarcomeres''', bound by Z-discs

**Myofibrils are arranged as '''sarcomeres''', bound by Z-discs, which are the functional unit of muscle contraction

**Each sarcomere contains 2 separate groups of myofilaments:

**Each sarcomere contains 2 separate groups of myofilaments:

***Thin filament, containing '''Actin''', located centrally

***Thin filament, containing '''Actin''', located centrally