1. Chapter 12a
Muscles

2. Mechanics of body movement Smooth muscle Cardiac muscle
About this Chapter
Skeletal muscle
Mechanics of body movement
Smooth muscle
Cardiac muscle

3. Three Types of Muscle Nucleus Muscle fiber (cell) Striations
(a) Skeletal muscle
Figure 12-1a

4. Three Types of Muscle Striations Muscle fiber Intercalated disk
Nucleus
(b) Cardiac muscle
Figure 12-1b

5. Three Types of Muscle Muscle fiber Nucleus (c) Smooth muscle
Figure 12-1c

6. Usually attached to bones by tendons Origin: closest to the trunk
Skeletal Muscle
Usually attached to bones by tendons
Origin: closest to the trunk
Insertion: more distal
Flexor: brings bones together
Extensor: moves bones away
Antagonistic muscle groups: flexor-extensor pairs

7. Antagonistic Muscle Groups
Triceps muscle relaxes
Biceps muscle contracts (flexor)
(a) Flexion
Figure 12-2a

8. Antagonistic Muscle Groups
Triceps muscle contracts (extensor)
Biceps muscle relaxes
(b) Extension
Figure 12-2b

9. Organization of Skeletal Muscle
Tendon
Nerve and blood vessels
Connective tissue
Muscle fascicle: bundle of fibers
Connective tissue
Nucleus
Muscle fiber
(a)
Figure 12-3a (1 of 2)

10. Organization of Skeletal Muscle
Figure 12-3a (2 of 2)

11. Ultrastructure of Muscle
ANATOMY SUMMARY
ULTRASTRUCTURE OF MUSCLE
Mitochondria
Sarcoplasmic reticulum
Nucleus
Thick filament
Thin filament
T-tubules
Myofibril
Sarcolemma
(b)
A band
Sarcomere
Z disk
Z disk
Myofibril
(c)
M line
I band
H zone
Titin
(d)
Z disk
Z disk
M line
Myosin crossbridges
M line
Thick filaments
Thin filaments
Titin
(e)
Myosin heads
Troponin
Nebulin
Hinge region
Myosin tail
Tropomyosin
G-actin molecule
Myosin molecule
(f)
Actin chain
Figure 12-3b-f

12. Ultrastructure of Muscle
Mitochondria
Sarcoplasmic reticulum
Thick filament
Thin filament
Nucleus
T-tubules
Myofibril
Sarcolemma
(b)
Figure 12-3b

13. Ultrastructure of Muscle
Sarcomere
A band
Z disk
Z disk
Myofibril
(c)
M line
I band
H zone
Figure 12-3c

14. Ultrastructure of Muscle
Titin
(d)
Z disk
Z disk
M line
Myosin crossbridges
Figure 12-3d

15. Ultrastructure of Muscle
M line
Thick filaments
(e)
Myosin
heads
Hinge
region
Myosin tail
Myosin molecule
Figure 12-3e

16. Ultrastructure of Muscle
Thin filaments
Titin
Troponin
Nebulin
Tropomyosin
G-actin molecule
Actin chain
(f)
Figure 12-3f

17. Ultrastructure of Muscle
A band
Sarcomere
Z disk
Z disk
Myofibril
(c)
M line
I band
H zone
Titin
(d)
Z disk
Z disk
M line
Myosin
crossbridges
M line
Thick filaments
Thin filaments
Titin
(e)
Troponin
Nebulin
Myosin
heads
Hinge
region
Myosin tail
Tropomyosin
G-actin molecule
Myosin molecule
Actin chain
(f)
Figure 12-3c-f

18. T-Tubules and the Sarcoplasmic Reticulum
T-tubule brings action potentials into interior of muscle fiber.
Thin filament
Sarcolemma
Thick filament
Triad
Sarcoplasmic reticulum stores Ca2+
Terminal cisterna
Figure 12-4

19. The Two- and Three-Dimensional Organization of a Sarcomere
A band
I band
H zone
I band
Thin filament
Thick filament
(a)
Z disk
M line
Z disk
(b)
Z disk
Z disk
I band thin filaments only
H zone thick filaments only
M line thick filaments linked with accessory proteins
Outer edge of A band thick and thin filaments overlap
(c)
Figure 12-5

20. Anatomy Review Animation
PLAY
Interactive Physiology® Animation: Muscular System:
Anatomy Review: Skeletal Muscle Tissue

21. Muscle tension: force created by muscle
Muscle Contraction
Muscle tension: force created by muscle
Load: weight that opposes contraction
Contraction: creation of tension in muscle
Relaxation: release of tension
Steps leading up to muscle contraction:
Events at the neuromuscular junction
Excitation-contraction coupling
Contraction-relaxation cycle

22. Summary of Muscle Contraction
Figure 12-7

23. Events at the Neuromuscular Junction
PLAY
Events at the Neuromuscular Junction
PLAY
Interactive Physiology® Animation: Muscular System: Events at the Neuromuscular Junction

24. Changes in a Sarcomere During Contraction
I band
Myosin Z
A band Z
Actin
Muscle relaxed
Z line Z M Z
A band
Half of I band
H zone
Half of I band
Sarcomere shortens with contraction
Half of I band H
M line
Z line Z Z
A band constant
Muscle contracted I H I
H zone and I band both shorten
Figure 12-8

25. Sliding Filament Theory
PLAY
Interactive Physiology® Animation: Muscular System: Sliding Filament Theory

26. The Molecular Basis of Contraction
Troponin
G-Actin TN
Myosin head
Tropomyosin blocks binding site on actin
ADP Pi
(a) Relaxed state. Myosin head cocked.
Figure 12-9a

27. The Molecular Basis of Contraction1
Cytosolic Ca2+ 1
Ca2+ levels increase
in cytosol. 3
Tropomyosin shifts,
exposing binding
site on actin 2 2
Ca2+ binds to
troponin (TN). TN 3
Troponin-Ca2+
complex pulls
tropomyosin
away from actin’s
myosin-binding site. 5
Actin
moves
ADP
Power stroke 4 Pi 4
Myosin binds to
actin and completes
power stroke. 5
Actin filament
moves.
(b) Initiation of contraction
Figure 12-9b

28. The Molecular Basis of Contraction
G-actin molecule
Myosin binding sites
Myosin filament 1
ATP binds to myosin. Myosin releases actin.
Tight binding in the rigor state
ATP
ADP 2
Myosin hydrolyses ATP. Myosin head rotates and binds to actin. 4
Myosin releases ADP.
Contraction- relaxation
Actin filament moves toward M line.
Sliding filament
ADP
Ca2+ signal Pi Pi 3
Power stroke
Relaxed state with myosin heads cocked
Figure 12-10

29. The Molecular Basis of Contraction
G-actin molecule
Myosin
binding sites
Myosin
filament
Tight binding in the rigor state
Figure 12-10, step 0

30. The Molecular Basis of Contraction
G-actin molecule
Myosin
binding sites
Myosin
filament 1
ATP binds to myosin.
Myosin releases actin. T
ight binding in the rigor state
ATP
Figure 12-10, steps 0–1

31. The Molecular Basis of Contraction1
ATP binds to myosin.
Myosin releases actin. 2
Myosin hydrolyses ATP. Myosin
head rotates and binds to actin.
ADP
ATP Pi
Relaxed state with myosin heads cocked
Figure 12-10, steps 1–2

32. The Molecular Basis of Contraction2
Myosin hydrolyses ATP. Myosin
head rotates and binds to actin. 3
Power stroke
Actin filament moves
toward M line.
Ca2+
signal
ADP Pi Pi
Relaxed state with
myosin heads cocked
Figure 12-10, steps 2–3

33. The Molecular Basis of Contraction3
Power stroke 4
Myosin releases ADP.
Actin filament moves
toward M line.
ADP Pi
Figure 12-10, steps 3–4

34. Excitation-Contraction Coupling
Axon terminal of
somatic motor neuron 1
Muscle fiber 1
Somatic motor neuron releases
ACh at neuromuscular junction.
ACh 2 2
Net entry of Na+ through ACh
receptor-channel initiates a
muscle action potential
Na+
Motor end plate
RyR
T-tubule
Ca2+
Sarcoplasmic
reticulum
DHP
Z disk
Troponin
Actin
Tropomyosin
M line
Myosin head
Myosin thick filament
(a) Initiation of muscle action potential
KEY
DHP = dihydropyridine L-type calcium channel
RyR = ryanodine receptor-channel
Figure 12-11a

35. Excitation-Contraction Coupling
Axon terminal of
somatic motor neuron 1
Muscle fiber 1
Somatic motor neuron releases
ACh at neuromuscular junction.
ACh
Motor end plate
RyR
T-tubule
Ca2+
Sarcoplasmic
reticulum
DHP
Z disk
Troponin
Actin
Tropomyosin
M line
Myosin head
Myosin thick filament
(a) Initiation of muscle action potential
KEY
DHP = dihydropyridine L-type calcium channel
RyR = ryanodine receptor-channel
Figure 12-11a, step 1

36. Excitation-Contraction Coupling
Axon terminal of
somatic motor neuron 1
Muscle fiber 1
Somatic motor neuron releases
ACh at neuromuscular junction.
ACh 2 2
Net entry of Na+ through ACh
receptor-channel initiates a
muscle action potential
Na+
Motor end plate
RyR
T-tubule
Ca2+
Sarcoplasmic
reticulum
DHP
Z disk
Troponin
Actin
Tropomyosin
M line
Myosin head
Myosin thick filament
(a) Initiation of muscle action potential
KEY
DHP = dihydropyridine L-type calcium channel
RyR = ryanodine receptor-channel
Figure 12-11a, steps 1–2

37. Excitation-Contraction Coupling3
Action potential in t-tubule alters
conformation of DHP receptor. 4
DHP receptor opens RyR Ca2+
release channels in sarcoplasmic
reticulum and Ca2+ enters
cytoplasm. 4 3 5
Ca2+ binds to troponin, allowing
actin-myosin binding. 7
Ca2+ released 5 6
Myosin heads execute power
stroke. 6
Myosin thick filament 7
Actin filament slides toward center
of sarcomere.
Distance actin moves
KEY
(b) Excitation-contraction coupling
DHP = dihydropyridine L-type calcium channel
RyR = ryanodine receptor-channel
Figure 12-11b

38. Electrical and Mechanical Events in Muscle Contraction
A twitch is a single contraction-relaxation cycle
Muscle fiber
+30
Action potential from CNS
Neuron membrane potential in mV
-70
Motor end plate
Recording electrodes
Time
Axon terminal
+30
Muscle fiber membrane potential in mV
Muscle action potential
-70
2 msec
Time
Latent period
Contraction phase
Relaxation phase
Development of tension during one muscle twitch
Tension
10–100 msec
Time
Figure 12-12

39. Phosphocreatine
Creatine phosphate
Glycolysis
Krebs cycle
Figure 12-13

40. Locations and Possible Causes of Muscle Fatigue
Figure 12-14

41. Causes of Muscle Fatigue During Exercise
Extended submaximal exercise
Depletion of glycogen stores
Short-duration maximal exertion
Increased levels of inorganic phosphate
May slow Pi release from myosin
Decrease calcium release
Maximal exercise
Potassium (K+) leaves muscle fiber, leading to increased concentration that is believed to decrease Ca2+

42. Skeletal Muscle Metabolism During Fatiguing Submaximal Exercise
Question 12-1

43. Fast-Twitch Glycolytic and Slow-Twitch Oxidative Muscle Fibers
Figure 12-15

44. Fast-Twitch Glycolytic and Slow-Twitch Oxidative Muscle Fibers
Table 12-2

45. Length-Tension Relationships in Contracting Skeletal Muscle
Figure 12-16