Skeletal Muscle
Microscopic
Anatomy
Chapter 10
Microscopic
Anatomy
• Muscle fibers = muscle
cells: long and
multinucleate
• Sarcolemma: cell
membrane
• Sarcoplasm: cytoplasm;
rich in oxygen-storing
myoglobin 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
•T tubules (transverse
tubules): narrow tubes
that are continuous
with sarcolemma,
conduct impulses
• Sarcoplasmic
reticulum (smooth ER):
stores Ca++ (muscle
contraction begins when
stored Ca++ ions are
released into
sarcoplasm)
• Mitochondria: provide
ATP for contraction
Closer Look at Myofibril
Composition
• thin filaments: actin (plus
tropomyosin & troponin)
Fig. 10.5
• thick filaments:
myosin
Sarcomere
Structure
• Z lines: the boundary
between sarcomeres
• 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