Skeletal Muscle Microscopic

AnatomyChapter 10

Microscopic Anatomy

• Muscle fibers = muscle cells: long and multinucleate

• Sarcolemma: cell membrane

• Sarcoplasm: cytoplasm; rich in oxygen-storing myoglobinmyoglobin protein

• Myofibrils: bundles of contractile proteins; fill most of the cytoplasm; 100’s to 1000’s per cell

• Sarcomeres: the repeating functional unit of contraction in each myofibril

• Sarcoplasmic reticulum (smooth ER): stores Ca+

+ (muscle contraction begins when stored Ca++ ions are released into sarcoplasm)

• Mitochondria: provide ATP for contraction

•T tubules (transverse tubules): narrow tubes that are continuous with sarcolemma, conduct impulses

Closer Look at Myofibril Composition

• thin filaments: actin (plus tropomyosin & troponin)

• thick filaments: myosin

Fig. 10.5

Sarcomere Structure

• Z lines: the boundary between sarcomeressarcomeres

• A band: overlap of thick (myosin) filaments & thin (actin) filaments

• I band: thin (actin) filaments only

• H zone: thick (myosin) filaments only

Fig. 10.3