1. Chapter 12
Muscles

2. About this Chapter Muscle types What muscles do How muscles contract
Contraction to locomotion
Roles of smooth muscles

3. Muscles
Contract!
Generate motion
Generate force
Generate heat
Support

4. Muscular System Functions
Body movement (Locomotion)
Maintenance of posture
Respiration
Diaphragm and intercostal contractions
Communication (Verbal and Facial)
Constriction of organs and vessels
Peristalsis of intestinal tract
Vasoconstriction of b.v. and other structures (pupils)
Heart beat
Production of body heat (Thermogenesis)

5. Properties of Muscle
Excitability: capacity of muscle to respond to a stimulus
Contractility: ability of a muscle to shorten and generate pulling force
Extensibility: muscle can be stretched back to its original length
Elasticity: ability of muscle to recoil to original resting length after stretched

6. Muscle Types Cardiac – heart Smooth – internal organs
Skeletal – "voluntary"
Attach to bone
Move appendages
Support body
Antagonistic pairs
Flexors
Extensors

7. Categories of skeletal muscle actions
Categories Actions
Extensor Increases the angle at a joint
Flexor Decreases the angle at a joint
Abductor Moves limb away from midline of body
Adductor Moves limb toward midline of body
Levator Moves insertion upward
Depressor Moves insertion downward
Rotator Rotates a bone along its axis
Sphincter Constricts an opening

8. Types of Muscle Skeletal Smooth Cardiac Attached to bones
Makes up 40% of body weight
Responsible for locomotion, facial expressions, posture, respiratory movements, other types of body movement
Voluntary in action; controlled by somatic motor neurons
Smooth
In the walls of hollow organs, blood vessels, eye, glands, uterus, skin
Some functions: propel urine, mix food in digestive tract, dilating/constricting pupils, regulating blood flow,
In some locations, autorhythmic
Controlled involuntarily by endocrine and autonomic nervous systems
Cardiac
Heart: major source of movement of blood
Autorhythmic

9. Connective Tissue Sheaths
Connective Tissue of a Muscle
Epimysium. Dense regular c.t. surrounding entire muscle
Separates muscle from surrounding tissues and organs
Connected to the deep fascia
Perimysium. Collagen and elastic fibers surrounding a group of muscle fibers called a fascicle
Contains b.v and nerves
Endomysium. Loose connective tissue that surrounds individual muscle fibers
Also contains b.v., nerves, and satellite cells (embryonic stem cells function in repair of muscle tissue
Collagen fibers of all 3 layers come together at each end of muscle to form a tendon or aponeurosis.

10. Muscle Types
Figure 12-1: Three types of muscles

11. Muscle Tissue Types

12. Skeletal Muscle Anatomy
About 40% body mass
Muscle fibers – cells
Fascicle – bundle
Motor unit
Muscle
sheath
Attach to tendons (which attach to bone)

13. Nerve and Blood Vessel Supply
Motor neurons
stimulate muscle fibers to contract
Neuron axons branch so that each muscle fiber (muscle cell) is innervated
Form a neuromuscular junction (= myoneural junction)
Capillary beds surround muscle fibers
Muscles require large amounts of energy
Extensive vascular network delivers necessary oxygen and nutrients and carries away metabolic waste produced by muscle fibers

14. Skeletal Muscle Anatomy
Figure 12-3a-1: ANATOMY SUMMARY: Skeletal Muscle

15. Skeletal Muscle Anatomy
Figure 12-3a-2: ANATOMY SUMMARY: Skeletal Muscle

16. Muscle Fiber Structure
Multiple nuclei
Sarcolemma
T-tubules
Sarcoplasmic reticulum
Sarcoplasm
Mitochondria
Glycogen & ions
Myofibrils

17. Muscle Fiber Structure
Figure 12-3b: ANATOMY SUMMARY: Skeletal Muscle

18. Muscle Fiber Structure
Figure 12-4: T-tubules and the sarcoplasmic reticulum

19. Myofibrils: Site of Contraction
Actin – "thin fibers"
Tropomysin
Troponin
Myosin – "thick fibers"
Titin – elastic anchor
Nebulin – non-elastic

20. Myofibrils: Site of Contraction
Figure 12-3c-f: ANATOMY SUMMARY: Skeletal Muscle

21. Sarcomere: Organization of Fibers
Z disks
I band
A band
H Zone
M line
Titin
Nebulin
Figure 12-5: The two- and three-dimensional organization of a sarcomere

22. Sarcomere: Organization of Fibers
Figure 12-6: Titin and nebulin

23. Skeletal Muscle Contraction: Mechanism
Figure 12-11a: Excitation-contraction coupling

24. Skeletal Muscle Contraction: Mechanism
Figure 12-11b: Excitation-contraction coupling

25. Energy for Contraction: ATP & Phosphocreatine
Aerobic Respiration
Oxygen
Glucose
Fatty acids
30-32 ATPs
Anaerobic Respiration
Fast but
2 ATP/glucose
Phosphocreatine ATPs

26. Energy for Contraction: ATP & Phosphocreatine
Figure 12-13: Phosphocreatine

28. Fiber Contraction Speed: Fast Twitch
Rate
2-3 times faster
SR uptake of Ca2+
ATP splitting
Anaerobic/Fatigue easily
Power lifting
Fast/delicate
Sprint

29. Fiber Contraction Speed: Fast Twitch
Figure 12-15: Fast-twitch glycolytic and slow-twitch muscle fibers

30. Fiber Contraction Speed: Oxidative Fast & Slow
Oxidative Fast Twitch
Intermediate speed
Anaerobic & aerobic
Slow Twitch: Aerobic, less fatigue
More mitochondria
More capillaries
Myoglobin
Endurance activities
Postural muscles

31. Coordinating the Fibers: Force of Contraction
Excitation and Twitch
Length–Tension: more crossbridges: more tension
Figure 12-16: Length-tension relationships in contracting skeletal muscle

32. Coordinating the Fibers: Summation to Tetanus
Figure 12-17: Summation of contractions

33. Smooth Muscle Fusiform cells One nucleus per cell Nonstriated
Involuntary
Slow, wave-like contractions
Smooth muscle is found in the walls of hollow organs. *Their muscle cells are fusiform in shape. *Smooth muscle cells have just on nucleus per cell. *Smooth muscle is nonstriated. *Smooth muscle is involuntary. *The contractions of smooth muscle are slow and wave-like.

34. Smooth Muscle Cells are not striated
Fibers smaller than those in skeletal muscle
Spindle-shaped; single, central nucleus
More actin than myosin
No sarcomeres
Not arranged as symmetrically as in skeletal muscle, thus NO striations.
Caveolae: indentations in sarcolemma;
May act like T tubules
Dense bodies instead of Z disks
Have noncontractile intermediate filaments

35. Smooth Muscle Grouped into sheets in walls of hollow organs
Longitudinal layer – muscle fibers run parallel to organ’s long axis
Circular layer – muscle fibers run around circumference of the organ
Both layers participate in peristalsis

36. Smooth Muscle Is innervated by autonomic nervous system (ANS)
Visceral or unitary (single unit) smooth muscle
Only a few muscle fibers innervated in each group
Impulse spreads through gap junctions
Whole sheet contracts as a unit
Often autorhythmic
Multiunit:
Cells or groups of cells act as independent units
Arrector pili of skin and iris of eye

37. Smooth Muscle Cell

38. Smooth Muscle Contraction: Mechanism

39. Smooth Muscle Relaxation: Mechanism

41. Contractile fibers are arranged in oblique bundles rather than in parallel sarcomeres

44. Myosin of Smooth Muscle
Different isoform than that found in skeletal muscle
Smooth muscle myosin ATPase activity is much slower, contraction is longer
Myosin light chain in the myosin head regulates contraction and relaxation

45. Smooth Muscle Relatively little sarcoplasmic reticulum Lacks T-tubules
Chemically linked to the cell membrane, rather than mechanically linked
Ca +2 storage is supplemented by caveolae , small vesicles that cluster close to the cell membrane. Voltage/ligand gated Ca +2 channels

46. Single-Unit Muscle

47. Properties of Single-Unit Smooth Muscle
Gap junctions
Pacemaker cells with spontaneous depolarizations
Innervation to few cells
Tone = level of contraction without stimulation
Increases/decreases in tension
Graded Contractions
No recruitment
Vary intracellular calcium
Stretch Reflex
Relaxation in response to sudden or prolonged stretch

48. Multi-Unit Muscle

49. Comparisons Among Skeletal, Smooth, and Cardiac Muscle