THE MUSCULAR SYSTEM

1. The Muscular System
• Muscles are responsible for all types of
body movement
• Three basic muscle types are found in the
body
– Skeletal muscle
– Cardiac muscle
– Smooth muscle

2. Function of Muscles
• Produce movement
• Maintain posture
• Stabilize joints
• Generate heat

3. Characteristics of Muscles
• Muscle cells are elongated
(muscle cell = muscle fiber)
• Contraction of muscles is due to the
movement of microfilaments
• All muscles share some terminology
– Prefix myo refers to muscle (myocardial)
– Prefix mys refers to muscle (myastenia gravis)
– Prefix sarco refers to flesh (sarcolema)

4. Skeletal Muscle Characteristics
• Most are attached by tendons to bones
• Cells are multinucleate
• Striated – have visible banding
• Voluntary – subject to conscious control
• Cells are surrounded and bundled by
connective tissue

5. Connective Tissue Wrappings of
Skeletal Muscle
• Endomysium – around
single muscle fiber
• Perimysium – around a
fascicle (bundle) of
fibers
• Epimysium – covers
the entire skeletal
muscle
• Fascia – on the outside
of the epimysium
Figure 6.1

6. 9-6
Connective Tissue, Nerve,
Blood Vessels
• Connective tissue
– External lamina
– Endomysium
– Perimysium
– Fasciculus
– Epimysium
• Fascia
• Nerve and blood
vessels
– Abundant

7. Skeletal Muscle Attachments
• Epimysium blends into a connective tissue
attachment
– Tendon – cord-like structure
– Aponeuroses – sheet-like structure
• Sites of attachment
– Bones
– Cartilages
– Connective tissue coverings

8. Smooth Muscle Characteristics
• Has no striations
• Spindle-shaped
cells
• Single nucleus
• Involuntary – no
conscious control
• Found in walls of
hollow organs
Figure 6.2a

9. Cardiac Muscle Characteristics
• Has striations
• involuntary
• Usually has a
single nucleus
• Joined to another
muscle cell at an
intercalated disc
• Found only in the heart
Figure 6.2b

10. 9-10
Parts of a Muscle

11. 9-11
Skeletal Muscle Structure
• Muscle fibers or
cells
– Develop from
myoblasts
– Numbers remain
constant
• Connective tissue
• Nerve and blood
vessels

12. 9-12
Components of Sarcomeres

13. Microscopic Anatomy of
Skeletal Muscle
• Cells are multinucleate
• Nuclei are just beneath the sarcolemma
• Sarcolemma–specialized plasma membrane
Figure 6.3a

14. Figure 6.3b
Microscopic Anatomy of
Skeletal Muscle
• Myofibril
– Bundles of myofilaments
– Myofibrils are aligned to give distinct bands
• I band =
light band
• A band =
dark band

15. Microscopic Anatomy of
Skeletal Muscle
• Sarcomere
– Contractile unit of a muscle fiber
Figure 6.3b

16. Microscopic Anatomy of
Skeletal Muscle
• Organization of the sarcomere
– Thick filaments = myosin filaments
• Composed of the protein myosin
Figure 6.3c

17. Microscopic Anatomy of
Skeletal Muscle
• Myosin filaments have heads (extensions, or
cross bridges)
• Myosin and actin overlap somewhat
• Sarcoplasmic reticulum (SR) – stores calcium

18. 9-18
Structure of Actin and Myosin

19. 9-19
Sarcomere Shortening

20. Properties of Skeletal Muscle
Activity
• Irritability – ability to receive and respond
to a stimulus
• Contractility – ability to shorten when an
adequate stimulus is received

21. Muscle is Stimulated by Nerve
• Skeletal muscles
must be
stimulated by a
nerve to contract
• Motor unit
– One neuron
– Muscle cells
stimulated by that
neuron
Figure 6.4a

22. Nerve Stimulus to Muscles
• Neuromuscular junctions – the site of
nerve and muscle association
Figure 6.5b

23. Nerve Stimulus to Muscles
• Synaptic cleft – gap
between nerve and
muscle
– Nerve and muscle
do not make contact
– Area between nerve
and muscle is filled
with interstitial fluid
Figure 6.5b

24. Transmission of Nerve Impulse
• Neurotransmitter – a chemical released by the
nerve upon arrival of nerve impulse
– The neurotransmitter - acetylcholine
• Neurotransmitter attaches to receptors on the
sarcolemma
• Sarcolemma becomes permeable to sodium
(Na+)
• Sodium enters the cell and generates an action
potential
• Once started, muscle contraction cannot be
stopped

25. The Sliding Filament Theory of
Muscle Contraction
• This action causes
the myosin to slide
along the actin
• The result is
shortening of the
muscle – a
contraction
Figure 6.7

26. The Muscular System (b)

27. Contraction of a Skeletal Muscle
• Muscle fiber contraction is “all or none”
• Within a skeletal muscle, not all fibers may
be stimulated during the same interval
• Different combinations of muscle fiber
contractions may give differing responses
• Graded responses – different degrees of
skeletal muscle shortening

28. Types of Graded Responses
• Twitch
– Single, brief contraction
– Not a normal muscle function
• Tetanus (summing of contractions)
– One contraction is immediately followed by
another
– The muscle does not completely return to a
resting state
– The effects are added
Figure 6.9a–b

29. Types of Graded Responses
• Unfused (incomplete) tetanus
– Some relaxation occurs between contractions
– The results are summed
• Fused
– No evidence of relaxation before the following
contractions
– The result is a sustained muscle contraction
Figure 6.9c–d

30. Muscle Response to Strong
Stimuli
• Muscle force depends upon the number of
fibers that are stimulated
• More fibers contracting results in greater
muscle tension
• Muscles can continue to contract unless
they run out of energy

31. Energy for Muscle Contraction
• Muscles use stored ATP for energy
– Bonds of ATP are broken to release energy
• After this initial use, other pathways must
be utilized to produce ATP
• Direct phosphorylation
– Muscle cells contain creatine phosphate
– After ATP is depleted, ADP is left
– CP transfers energy to ADP, to regenerate
ATP

32. Energy for Muscle Contraction
• Aerobic Respiration
(Cellular respiration)
– Series of metabolic pathways
that occur in the mitochondria
– Glucose is broken down to
carbon dioxide and water,
releasing energy
– This is a slower reaction that
requires continuous oxygen
Figure 6.10b

33. Energy for Muscle Contraction
• Anaerobic glycolysis
– Reaction that breaks
down glucose without
oxygen
– Glucose is broken down
to pyruvic acid to produce
some ATP
– Pyruvic acid is converted
to lactic acid

34. Muscle Fatigue and Oxygen Debt
• When a muscle is fatigued, it is unable to
contract
• The common reason for muscle fatigue is
oxygen debt
– Oxygen must be placed
– Oxygen is required to rid of accumulated
lactic acid
• Increase acidity (from lactic acid) and lack
of ATP causes the muscle to contract less

35. 2 Types of Muscle Contractions
• Isotonic contractions
– Myofilaments are able to slide past each other
during contractions
– Tension in the muscles increases
– The muscle shortens
• Isometric contractions
– Tension in the muscles increases
– The muscle is unable to shorten

36. Muscles and Body Movements
• Movement is
attained due to a
muscle moving an
attached bone
Figure 6.12

37. Muscles and Body Movements
• Muscles are
attached to at least
two points
– Origin – attachment
to a moveable bone
– Insertion –
attachment to an
immovable bone
Figure 6.12

38. Effects of Exercise on Muscle
• Results of increased muscle use
– Increase in muscle size
– Increase in muscle strength
– Increase in muscle efficiency
– Muscle becomes more fatigue resistant

39. Ordinary Body Movements
• Flexion
• Extension
• Rotation
• Abduction
• Circumduction

40. Special Movements
• Dorsifelxion
• Plantar flexion
• Inversion
• Eversion
• Supination
• Pronation
• Opposition

41. Types of Muscles
• Prime mover – muscle with the major
responsibility for a certain movement
• Antagonist – muscle that opposes or
reverses a prime mover
• Synergist – muscle that aids a prime
mover in a movement and helps prevent
rotation
• Fixator – stabilizes the origin of a prime
mover

42. Naming of Skeletal Muscles
• Direction of muscle fibers
– Example: rectus (straight)
• Relative size of the muscle
– Example: maximus (largest)

43. Naming of Skeletal Muscles
• Location of the muscle
– Example: many muscles are named for bones
(e.g., temporalis)
• Number of origins
– Example: triceps (three heads)

44. Naming of Skeletal Muscles
• Location of muscle’s origin and insertion
– Example: sterno (on the sternum)
• Shape of the muscle
– Example: deltoid (triangular)
• Action of the muscle
– Example: flexor and extensor (flexes or
extends a bone)

45. Superficial
Muscles:
Anterior

46. Superficial
Muscles:
Posterior
Figure 6.22

47. Head and Neck Muscles
Figure 6.15

48. Trunk Muscles
Figure 6.16

49. Deep Trunk and Arm Muscles
Figure 6.17

50. Pelvis, Hip, and Thigh Muscles
Figure 6.19c

51. Muscles of the Lower Leg
Figure 6.20