1. Muscle and the Sliding filament theory

2. Skeletal muscle development
Myoblasts
one nucleus each
lacking myofibrils
Myotubes
develop myofibrils
Many nuclei
FUSE

3. Skeletal and Cardiac Muscle
Both demonstrate “striations” or stripes when seen with a microscope
These stripes represent the regular arrangement of actin and myosin

4. Myosin is a thick protein and looks dark in the section
Actin is a very small protein and looks pale in the section.
The dark ovals
are the nuclei of the
muscle cells.
There may be up to
A 100 nuclei per cell

5. Sarcomeres Functional contractile unit of striated muscle
2-3 mm in length
Striations
Made up of regular overlapping pattern
of actin (thin filaments)
myosin (thick filaments)
Delineated by Z lines
Center line is I band

6. Very close image of muscle
A band: myosin
I band: actin
Z lines: where the actin
attaches and the end
of a sarcomere

7. Muscle contraction When muscle contracts, The Z discs will come closer
all of the actin
(white in the picture, red in the diagram)
will slide over
the myosin
(black in the picture, green in the diagram).
The Z discs will come closer
All of these millions of shortenings in one muslce will result in muscle contractions

8. Sliding filament mechanism
Sarcomeres shortened
Thin filaments slide over thick filament
Requires ATP
The cells source of energy
other proteins and calcium

9. Animation of sliding filament