1. Table 9.3

2. Special Characteristics of Muscle Tissue
Excitability (responsiveness or irritability): ability to receive and respond to stimuli
Contractility: ability to shorten when stimulated
Extensibility: ability to be stretched
Elasticity: ability to recoil to resting length

3. Muscle Functions
Movement of bones or fluids (e.g., blood)
Maintaining posture and body position
Stabilizing joints
Heat generation (especially skeletal muscle)

4. Skeletal Muscle
Each muscle is served by one artery, one nerve, and one or more veins

5. (wrapped by perimysium)
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)
Figure 9.1

9. Microscopic Anatomy of a Skeletal Muscle Fiber
Cylindrical cell 10 to 100 m in diameter, up to 30 cm long
Multiple nuclei
Many mitochondria
Glycogen storage, myoglobin for O2 storage

10. 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 afrom the cut end of the fiber.

11. 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.
Figure 9.2c, d

12. Longitudinal section of filaments within one sarcomere of a myofibril
Thick filament
Thin filament
In the center of the sarcomere, the thick
filaments lack myosin heads. Myosin heads
are present only in areas of myosin-actin overlap.
Thick filament
Thin filament
Each thick filament consists of many
myosin molecules whose heads protrude
at opposite ends of the filament.
A thin filament consists of two strands
of actin subunits twisted into a helix
plus two types of regulatory proteins
(troponin and tropomyosin).
Portion of a thick filament
Portion of a thin filament
Myosin head
Tropomyosin
Troponin
Actin
Actin-binding sites
Heads
Tail
Active sites
for myosin
attachment
ATP-
binding
site
Actin
subunits
Flexible hinge region
Myosin molecule
Actin subunits
Figure 9.3

13. 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
Figure 9.5

14. 1 2 Figure 9.6 Z H Z I A I Fully relaxed sarcomere of a muscle fiber Z
Fully contracted sarcomere of a muscle fiber
Figure 9.6

15. Myelinated axon
of motor neuron
Action
potential (AP)
Axon terminal of
neuromuscular
junction
Nucleus
Sarcolemma of
the muscle fiber
Action potential arrives at
axon terminal of motor neuron. 1
Ca2+
Synaptic vesicle
containing ACh
Ca2+
Voltage-gated Ca2+ channels
open and Ca2+ enters the axon
terminal. 2
Mitochondrion
Synaptic
cleft
Axon terminal
of motor neuron
Fusing synaptic
vesicles
Figure 9.8
Figure 9.8

16. Figure 9.8 1 2 3 4 5 6 Myelinated axon of motor neuron Action
potential (AP)
Axon terminal of
neuromuscular
junction
Nucleus
Sarcolemma of
the muscle fiber
Action potential arrives at
axon terminal of motor neuron. 1
Ca2+
Synaptic vesicle
containing ACh
Ca2+
Voltage-gated Ca2+ channels
open and Ca2+ enters the axon
terminal. 2
Mitochondrion
Synaptic
cleft
Axon terminal
of motor neuron
Ca2+ entry causes some
synaptic vesicles to release
their contents (acetylcholine)
by exocytosis. 3
Fusing synaptic
vesicles
Junctional
folds of
sarcolemma
ACh
Acetylcholine, a
neurotransmitter, diffuses across
the synaptic cleft and binds to
receptors in the sarcolemma. 4
Sarcoplasm of
muscle fiber
ACh binding opens ion
channels that allow simultaneous
passage of Na+ into the muscle
fiber and K+ out of the muscle
fiber. 5
Na+ K+
Postsynaptic membrane
ion channel opens;
ions pass.
ACh effects are terminated
by its enzymatic breakdown in
the synaptic cleft by
acetylcholinesterase. 6
Ach–
Degraded ACh
Postsynaptic membrane
ion channel closed;
ions cannot pass.
Na+
Acetyl-
cholinesterase K+
Figure 9.8

17. Terminal cisterna of SR
Setting the stage
Axon terminal
of motor neuron
Synaptic cleft
Action potential
is generated
ACh
Sarcolemma
Terminal cisterna of SR
Muscle fiber
Ca2+
Triad
One sarcomere
Figure 9.11, step 1

18. Figure 9.11, step 2 Steps in E-C Coupling: The aftermath Sarcolemma
Voltage-sensitive
tubule protein
T tubule 1
Action potential is propagated along
the sarcolemma and down the T tubules.
Ca2+
release
channel
Calcium ions are released. 2
Terminal
cisterna
of SR
Ca2+
Actin
Troponin
Tropomyosin
blocking active sites
Ca2+
Myosin
Calcium binds to troponin and
removes the blocking action of
tropomyosin. 3
Active sites exposed and
ready for myosin binding
Contraction begins 4
Myosin
cross
bridge
The aftermath
Figure 9.11, step 2

19. Figure 9.12 Thin filament Actin Ca2+ Myosin cross bridge Thick
ADP Pi
Thick
filament
Myosin 1
Cross bridge formation.
ADP
ADP Pi
ATP
hydrolysis Pi 4
Cocking of myosin head. 2
The power (working)
stroke.
ATP
ATP 3
Cross bridge
detachment.
Figure 9.12

20. Motor Unit: The Nerve-Muscle Functional Unit
Motor unit = a motor neuron and all (four to several hundred) muscle fibers it supplies

21. neuromuscular junctions
Spinal cord
Motor neuron
cell body
Muscle
Nerve
Motor
unit 1
unit 2
fibers
neuron
axon
Axon terminals at
neuromuscular junctions
Axons of motor neurons extend from the spinal cord to the
muscle. There each axon divides into a number of axon
terminals that form neuromuscular junctions with muscle
fibers scattered throughout the muscle.
Figure 9.13a

22. Motor Unit
Small motor units in muscles that control fine movements (fingers, eyes)
Large motor units in large weight-bearing muscles (thighs, hips)

23. Motor Unit
Muscle fibers from a motor unit are spread throughout the muscle so that a single motor unit causes weak contraction of entire muscle
Motor units in a muscle usually contract asynchronously; helps prevent fatigue

24. Motor unit 1 Recruited (small fibers) unit 2 recruited (medium unit 3
(large
Figure 9.17

25. Muscle Tone
Constant, slightly contracted state of all muscles
Due to spinal reflexes that activate groups of motor units alternately in response to input from stretch receptors in muscles
Keeps muscles firm, healthy, and ready to respond

26. Muscle Metabolism: Energy for Contraction
ATP is the only source used directly for contractile activities
Available stores of ATP are depleted in 4–6 seconds

27. Muscle Metabolism: Energy for Contraction
ATP is regenerated by:
Direct phosphorylation of ADP by creatine phosphate
Anaerobic pathway
Aerobic respiration

28. At 70% of max contractile activity:
Anaerobic Pathway
At 70% of max contractile activity:
Bulging muscles compress blood vessels
Oxygen delivery is impaired
Build up lactic acid

29. Glucose (from glycogen breakdown or delivered from blood)
Energy source: glucose
Glycolysis and lactic acid formation
(b) Anaerobic pathway
Oxygen use: None
Products: 2 ATP per glucose, lactic acid
Duration of energy provision:
60 seconds, or slightly more
Glucose (from
glycogen breakdown or
delivered from blood)
Glycolysis
in cytosol
Pyruvic acid
Released
to blood
net gain 2
Lactic acid O2
ATP
Figure 9.19b

30. Effects of Exercise Aerobic (endurance) exercise: Leads to increased:
Muscle capillaries
Number of mitochondria
Myoglobin synthesis
Results in greater endurance, strength, and resistance to fatigue
May convert fast glycolytic fibers into fast oxidative fibers

31. Effects of Resistance Exercise
Resistance exercise (typically anaerobic) results in:
Muscle hypertrophy (due to increase in fiber size)
Increased mitochondria, myofilaments, glycogen stores, and connective tissue

32. The Overload Principle
Forcing a muscle to work hard promotes increased muscle strength and endurance
Muscles adapt to increased demands
Muscles must be overloaded to produce further gains

33. Smooth Muscle
Found in walls of most hollow organs (except heart)
Usually in two layers (longitudinal and circular)

34. Longitudinal layer of smooth muscle (shows smooth muscle fibers in
cross section)
Small
intestine
Mucosa
(a)
(b) Cross section of the intestine showing the smooth muscle layers (one circular and the other longitudinal) running at right angles to each other.
Circular layer of
smooth muscle
(shows longitudinal
views of smooth
muscle fibers)
Figure 9.26

35. Peristalsis
Alternating contractions and relaxations of smooth muscle layers that mix and squeeze substances through the lumen of hollow organs
Longitudinal layer contracts; organ dilates and shortens
Circular layer contracts; organ constricts and elongates

36. Contraction of Smooth Muscle
Very energy efficient (slow ATPases)
Myofilaments may maintain for prolonged contractions

37. Special Features of Smooth Muscle Contraction
Hyperplasia:
Smooth muscle cells can divide and increase their numbers
Example:
estrogen effects on uterus at puberty and during pregnancy

38. Developmental Aspects
With age, connective tissue increases and muscle fibers decrease
By age 30, loss of muscle mass (sarcopenia) begins
Regular exercise reverses sarcopenia
Atherosclerosis may block distal arteries, leading to intermittent claudication and severe pain in leg muscles