1. Chapter 09 Lecture Outline
See separate PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes.

2. Introduction There are 3 types of muscle tissue
in the muscular system:
Skeletal muscle:
Attached to bones of skeleton
Voluntary (consciously controlled)
Cardiac muscle:
Makes up most of the wall of the
heart
Involuntary (non-consciously-
controlled)
Responsible for pumping action
of the heart
Smooth muscle:
Found in walls of internal organs,
such as those of digestive tract

3. 9.1: Structure of a Skeletal Muscle
Skeletal Muscles:
Attach to bones, and skin of face
Under conscious control (voluntary)
A skeletal muscle is an organ of the muscular system
Skeletal muscles are composed of:
Skeletal muscle tissue
Nervous tissue
Blood
Connective tissues

4. Connective Tissue Coverings
Muscle coverings:
Epimysium: surrounds
whole muscle
Perimysium: surrounds
fascicles within a muscle
Endomysium: surrounds
muscle fibers (cells) within
a fascicle

5. Connective Tissue and Fascicles
Epimysium
Perimysium
Endomysium
Epimysium + Perimysium + Endomysium = Tendon

6. Skeletal Muscle Fibers
Skeletal muscle fiber = muscle cell
Multinucleated
Sarcolemma
Sarcoplasm
Many myofibrils
Myofibrils consist of:
- thin actin filaments
- thick myosin filaments
Sarcomeres
Sarcoplasmic reticulum (SR)
Transverse (‘T’) tubule
Triad: 1 T tubule and 2
SR cisternae

7. Skeletal Muscle Fibers
Myofibrils consist of
sarcomeres connected
end-to-end
Striation pattern is made
by arrangement of
myofilaments in myofibrils
Sarcomeres contain these
structures:
I band (thin filaments)
A band (thick & thin
filaments)
H zone (thick filaments)
Z line (or Z disc)
M line

8. Skeletal Muscle Fibers
Striation pattern has 2 main parts:
I Band: Light band, composed
of thin actin filaments
A Band: Dark band, composed
of thick myosin filaments overlapping
with thin actin filaments
H Zone: Center of A band;
composed of thick myosin filaments
Z Line: Anchors filaments in place;
sarcomere boundary; center of I band
M Line: Anchors thick filaments;
center of A band

9. Skeletal Muscle Fibers
Thick filaments: Composed of myosin protein; heads form crossbridges Thin filaments: Composed of actin protein; associated with troponin and tropomyosin, which prevent crossbridge formation when muscle is not contracting

10. 9.2: Skeletal Muscle Contraction
Contraction of a muscle fiber:
Requires interaction from several chemical and cellular components
Results from a movement within the myofibrils, in which the actin and myosin filaments slide past one another, shortening the sarcomeres
Muscle fiber shortens and pulls on attachment points

11. Neuromuscular Junction
A type of synapse
Also called a myoneural junction
Site where an axon of motor neuron
and skeletal muscle fiber interact
Skeletal muscle fibers contract
only when stimulated by a motor
neuron
Parts of a NMJ:
Motor neuron
Motor end plate
Synaptic cleft
Synaptic vesicles
Neurotransmitters

12. Stimulus for Contraction
Acetylcholine (ACh) is the
neurotransmitter
Nerve impulse causes release
of ACh from synaptic vesicles
ACh binds to ACh receptors on
motor end plate
ACh causes changes in
membrane permeability
to Na+ and K+ ions, which
generates a muscle impulse
(action potential)
Impulse causes release of
Ca+2 from SR, which leads
to muscle contraction

13. Excitation-Contraction Coupling
Excitation-Contraction Coupling: Connection between muscle fiber stimulation and muscle contraction
During muscle relaxation:
Ca+2 ions are stored in SR
Troponin-tropomyosin complexes cover binding sites on actin filaments
Upon muscle stimulation:
Muscle impulses cause SR to release Ca+2 ions into cytosol
Ca+2 ion binds to troponin to change its shape
The position of tropomyosin is altered
Binding sites on actin are now exposed
Myosin heads bind to actin, forming cross-bridges

14. Excitation-Contraction Coupling

15. The Sliding Filament Model
of Muscle Contraction:
When sarcomeres shorten,
thick and thin filaments slide
past one another
H zones and I bands narrow
Z lines move closer together
Thin and thick filaments do
not change length
Overlap between filaments
increases

16. Cross-Bridge Cycling Myosin head attaches to
actin binding site, forming
cross-bridge
Myosin cross-bridge pulls
thin filament toward center
of sarcomere
ADP and phosphate are
released from myosin
New ATP binds to myosin
Linkage between actin and
myosin cross-bridge break
ATP splits
Myosin cross-bridge goes
back to original position

17. Relaxation When neural stimulation of muscle fiber stops:
Acetylcholinesterase (enzyme) rapidly decomposes ACh remaining in the synapse
Muscle impulse stops when ACh is decomposed
Stimulus to sarcolemma and muscle fiber membrane ceases
Calcium pump moves Ca+2 back into sarcoplasmic reticulum (SR)
Troponin-tropomyosin complex again covers binding sites on actin
Myosin and actin binding are now prevented
Muscle fiber relaxes

18. Energy Sources for Contraction
1. ATP reserves: small amount 2. Creatine phosphate: initial source of energy to regenerate ATP from ADP and P 3. Cellular respiration

19. Oxygen Supply & Cellular Respiration
Anaerobic Phase:
Glycolysis
Occurs in cytoplasm
Produces little ATP
Aerobic Phase:
Citric acid cycle and
electron transport system
Occurs in the mitochondria
Produces the most ATP
Myoglobin stores extra
oxygen in muscles

20. Oxygen Debt Anaerobic (Lactic Acid) Threshold: Oxygen debt:
During rest or moderate exercise, respiratory & cardiovascular systems supply enough O2 to support aerobic respiration
Anaerobic (Lactic Acid) Threshold:
Shift in metabolism from aerobic to anaerobic, during strenuous muscle activity, when the above systems cannot supply the necessary O2. Lactic acid is produced.
Oxygen debt:
Amount of oxygen needed by liver cells to convert the accumulated lactic acid to glucose, and to restore muscle ATP and creatine phosphate concentrations.

21. Oxygen Debt

22. Muscle Fatigue Muscle Fatigue: Muscle Cramp:
Inability to contract muscle
Common causes of muscle fatigue:
Decreased blood flow
Ion imbalances across the sarcolemma
Loss of desire to continue exercise
Accumulation of lactic acid (controversial)
Muscle Cramp:
Sustained, involuntary muscle contraction
May be caused by changes in electrolyte concentration in extracellular fluids in the area

23. Heat Production
Heat is a by-product of cellular respiration in active cells
Muscle cells are major source of body heat
More than half the energy released in cellular respiration becomes heat; less than half is transferred to ATP
Blood transports heat throughout body core

24. 9.3: Muscular Responses
Muscle contraction can be observed by removing a single skeletal muscle fiber and connecting it to a device that senses and records changes in the overall length of the muscle fiber.
Electrical stimulator promotes the contractions

25. Threshold Stimulus Threshold Stimulus:
Minimum strength of stimulation of a muscle fiber required to cause contraction
When strength of stimulus reaches threshold, an action potential is generated
Impulse spreads through muscle fiber, releasing Ca+2 from SR and activating crossbridge formation
One action potential from a motor neuron releases enough ACh to produce threshold stimulus in muscle fiber, causing a muscle impulse

26. Recording of a Muscle Contraction
Twitch:
Contractile response of a single
muscle fiber to a single impulse
Latent period
Period of contraction
Period of relaxation

27. Length-Tension Relationship
Length of muscle fiber before stimulation determines amount of force it can develop
Optimum starting length is resting length of the muscle fiber; this allows the greatest force to develop
Stretched muscle fibers develop less force, since some myosin heads cannot reach binding sites on actin
Shortened muscle fibers also develop less force, since compressed
sarcomeres cannot shorten further

28. Summation
Summation:
Process by which the force of individual muscle fiber twitches combine
Produces sustained contractions
Can lead to partial or complete tetanic contractions

29. Recruitment of Motor Units
A motor neuron + all of the
muscle fibers it controls
A whole muscle consists
of many motor units
Coarse movements are
produced with large numbers
of fibers in a motor unit
Precise movements are
produced with fewer muscle
fibers in a motor unit

30. Recruitment of Motor Units
Increase in the number of motor units activated, to produce more force
Certain motor units are activated first, and others are activated only when the intensity of stimulus increases
As intensity of stimulation increases, recruitment of motor units continues until all motor units are activated

31. Sustained Contractions
Smaller motor units (smaller diameter axons) - recruited first
Larger motor units (larger diameter axons) - recruited later
Summation and recruitment can produce sustained contractions of increasing strength
Whole muscle contractions are smooth movements
Muscle tone (tonus): Continuous state of partial contraction in resting muscles

32. Types of Contractions
Isotonic: muscle contracts and changes length; equal force
Concentric: shortening contraction
Eccentric: lengthening contraction
Isometric: muscle contracts but does not change length; change in force

33. Use and Disuse of Skeletal Muscles
Clinical Application
Use and Disuse of Skeletal Muscles
Hypertrophy: Enlargement of skeletal muscle that is exercised
Atrophy: Decrease in size and strength of skeletal muscle that is unused
Aerobic exercise stimulates slow-twitch fibers. In response, fibers increase their capillaries and mitochondria.
Forceful exercise stimulates mainly fast-twitch fibers. In response, fibers produce new actin & myosin filaments, and the muscle enlarges.

34. 9.4: Smooth Muscle
Compared to skeletal muscle fibers, smooth muscle fibers are:
Shorter
Single, centrally located nucleus
Elongated with tapering ends
Myofilaments randomly organized
Lack striations
Lack transverse tubules
Sarcoplasmic reticulum (SR) not well developed

35. Types of Smooth Muscle 2 types of smooth muscle:
Multi-unit Smooth Muscle:
Cells are less organized
Function as separate units
Fibers function independently
Iris of eye, walls of blood vessels
Stimulated by neurons, hormones
Visceral Smooth Muscle:
Single-unit smooth muscle; cells respond as a unit
Sheets of spindle-shaped muscle fibers
Fibers held together by gap junctions
Exhibit rhythmicity
Conduct peristalsis
Walls of most hollow organs
More common type of smooth muscle

36. Smooth Muscle Contraction
Resembles skeletal muscle contraction in these ways:
Interaction between actin and myosin
Both use calcium and ATP
Both are triggered by membrane impulses
Different from skeletal muscle contraction in these ways:
Smooth muscle lacks troponin; uses calmodulin instead
Two neurotransmitters affect smooth muscle: Acetylcholine (Ach) and norepinephrine (NE)
Hormones can stimulate or inhibit smooth muscle
Stretching can trigger smooth muscle contraction
Smooth muscle slower to contract and relax
Smooth muscle more resistant to fatigue
Smooth muscle can change length without changing tautness

37. 9.5: Cardiac Muscle Cardiac Muscle: Located only in the heart
Striated muscle cells
Muscle fibers joined together by intercalated discs
Fibers branch, contain a single nucleus
Network of fibers contracts as a unit (syncytium)
Self-exciting and rhythmic
Longer refractory period than skeletal muscle
No sustained or tetanic contractions

38. Characteristics of Muscle Tissues

39. 9.6: Skeletal Muscle Actions
Skeletal muscles generate a great variety of body movements
The action of each muscle mostly depends upon
- the type of joint it is associated with
- the way the muscle is attached on either side of the joint

40. Origin and Insertion
One end of a skeletal muscle is more fixed, and the other end is more movable: Origin: less movable end Insertion: more movable end When a muscle contracts, insertion is pulled toward origin

41. Interaction of Skeletal Muscles
Most skeletal muscle function in groups. Roles of muscles in performing certain actions:
Agonist: muscle that causes an action
Prime mover: agonist primarily responsible for movement
(In some cases, the terms “agonist” and “prime mover” are used
interchangeably)
Synergists: muscles that assist agonist / prime mover
Antagonist: muscles whose contraction causes movement in the opposite direction of the prime mover

42. 9.7: Major Skeletal Muscles
Anterior View of the Superficial Skeletal Muscles:

43. Major Skeletal Muscles
Posterior View of the
Superficial Skeletal
Muscles:

44. Muscles of Facial Expression

45. Muscles of Mastication

46. Muscles of Facial Expression and Mastication

47. Clinical Application 9.3 TMJ Syndrome
Temporomandibular Joint Syndrome:
Articulation problem between mandibular condyle of mandible and mandibular fossa of temporal bone
Affects nerves passing through neck and jaw region
Caused by misaligned jaw, grinding/clenching of teeth
Causes clicking jaw, facial pain, ringing in ears, insomnia, tooth sensitivity to heat/cold, backache, dizziness, ear pain
Treatments: physical therapy, oral appliances, arthrocentesis, injections of botulism toxin or steroids