1. Skeletal Muscle Contraction
Muse

2. Muscle cells are composed of many long fibers
Epimysium
Epimysium
Bone
Perimysium
Tendon
Endomysium
Muscle fiber
in middle of
a fascicle
(b)
Blood vessel
Fascicle
(wrapped by perimysium)
Endomysium
(between individual
muscle fibers)
Perimysium
Fascicle
Muscle fiber
(a)
Muscle cells are composed of many long fibers

3. Cells are polynucleate and surrounded by sarcolemma
Mitochondrion
Myofibril
Dark A band
Light I band
Nucleus
(b) Diagram of part of a muscle fiber showing the myofibrils. One myofibril is extended from the cut end of the fiber.
Cells are polynucleate and surrounded by sarcolemma

4. Skeletal Muscle Fibers

5. The overlap of fiber elements causes the striated appearance
Z disc
Z disc

6. The Sarcomere
Smallest contractile unit (functional unit) of a muscle fiber
The region of a myofibril between two successive Z discs
Composed of thick and thin myofilaments made of contractile proteins

7. Positions of the fibers relative to each other
Thin (actin)
filament
Z disc
H zone
Z disc
Thick (myosin)
filament
I band
A band
Sarcomere
I band
M line
(c)
Small part of one myofibril enlarged to show the myofilaments
responsible for the banding pattern. Each sarcomere extends from
one Z disc to the next.
Sarcomere
Z disc
M line
Z disc
Thin (actin)
filament
Elastic (titin)
filaments
Thick
(myosin)
filament
(d)
Enlargement of one sarcomere (sectioned lengthwise). Notice the
myosin heads on the thick filaments.
Thin filaments = actin Thick filaments = myosin

8. Actin is partially covered by tropomysosin

9. Myosin is a tree of heads
Myosin thick filament

10. 10_10 The signal to contract Action potential arrives at
neuromuscular junction.
acetocholine released
ligand gated sodium channels
open and action potential
continues along sarcolemma
10_10

11. 1 Action potential is propagated along the sarcolemma and down
the T tubules. 1
Steps in
E-C Coupling:
Sarcolemma
Voltage-sensitive
tubule protein
T tubule
Ca2+
release
channel
Terminal
cisterna
of SR
Ca2+
Figure 9.11, step 3

12. Sarcoplasmic reticulum releases Ca2+
Part of a skeletal
muscle fiber (cell)
I band
A band
I band
Z disc
H zone
Z disc
Myofibril
M line
Sarcolemma
Triad: •
T tubule •
Terminal
cisternae
of the SR (2)
Sarcolemma
Tubules of
the SR
Myofibrils
Mitochondria
Sarcoplasmic reticulum releases Ca2+

13. The Contraction Cycle Five Steps of the Contraction Cycle
Exposure of active sites on actin
Formation of cross-bridges
Pivoting of myosin heads
Detachment of cross-bridges
Reactivation of myosin

15. The length of the sarcomere shrinks as the
filaments undergo the contraction cycle

16. Cross bridge detachment requires ATP hydrolysis

17. Once detached, residual energy from detachment re-cocks myosin head

18. Tension builds quickly

19. review
10_11
10_11

20. Repeated action potentials lead to maximum tension

21. Different fiber types can be fast or slower to develop full tension.

22. Metabolic sources of energy for muscle contraction
10_12
10_12