Microscopic Anatomy of Skeletal Muscle

Week 7 – Muscular System (Laboratory Class)

• Skeletal muscles are multinucleate, by which oval nuclei can be seen beneath the _______ (also known as muscle hast; outermost covering of the skeletal muscle).

sarcolemma

• The nuclei are pushed aside by long ribbonlike organelles called _____ (nuclei are pushed aside; composed of alternating light and dark).

myofibrils

• bands give the muscle cell its striated appearance.

Alternating light (I) and dark (A)

• The light I band has a midline interruption called the ___

Z disc.

• The dark A band has a lighter central area called the ______

H zone/bare zone.

• structural and functional units of skeletal muscle.

• Responsible for the striations of skeletal muscle.

Sarcomeres

• extend the entire length of dark A band. Have ATPase Enzyme.

Thick filaments (myosin filaments)

• form cross bridges when they link thick and thin filaments together during contraction.

Myosin heads

• attached to Z disc by “titin".

Myosin filaments

• elastic filaments that run through the core of thick filaments.

Titin

• anchored to the Z disc.

• Do not extend into the middle of a relaxed sarcomere, thus the central region the H zone looks a bit lighter.

Thin filaments (actin filaments)

• very important muscle fiber organelle.

• Specialized smooth endoplasmic reticulum.

• Store calcium.

Sarcoplasmic Reticulum

2 proteins of Sarcoplasmic Reticulum

1. tropomyosin

2. troponin