1. The Muscular System
Chapter 6

2. Muscle Tissues Muscles make up nearly ½ of the body’s mass!
Function: contraction/shortening  movement!
Muscle Types (Table 6.1, page 182)
Skeletal
Cardiac
Smooth

3. Skeletal Muscle “fiber” – elongated cells Striated, voluntary
Skeletal muscle is organ of the Muscular System
Surrounded by fascia separated into:
Endomysium: surrounds each fiber
Perimysium: surrounds groups of fibers (fascicle)
Epimysium: covers entire muscle
Continuous with tendons or aponeuroses

4. Skeletal Muscle
Figure 6.1, page 183

5. Anatomy of a Skeletal Muscle “Bundles of Bundles”
Muscle (fascicles wrapped in epimysium)
Fascicles (muscle fibers wrapped in perimysium)
Fibers (elongated cells, enclosed with sarcolemma)
Myofibrils (organelles which fill sarcoplasm)
Myofilaments (threadlike protein filaments bundled
into myofibrils)

6. Muscle Function Producing movement Maintaining posture & body position
Muscles, bones, & joints work together
Maintaining posture & body position
Stabilizing joints
Generating heat (thermogenesis)
80% of heat comes from muscle contraction (lost when bonds in ATP broken)
Shivering to raise temperature when cold

7. link

8. Microscopic Anatomy of Skeletal Muscle
Cells are multinucleate
Sarcolemma: cell membrane
Myofibrils: ribbon-like organelles that fill the cytoplasm
Alternating light (I) and dark (A) bands on myofibrils (striations)
Sarcomere: contractile unit of muscle (myofibrils)
Aligned end to end
Myofilaments within myofibrils
Sarcoplasmic reticulum (SR): specialized smooth ER
Stores calcium and releases it on demand when muscle fiber stimulated to contract

9. Myofilaments Myosin filaments: thick filaments
Made of bundles of protein myosin
Contain ATPase enzymes (split ATP)
Extend length of A band
Ends have small projections called myosin heads (cross bridges): link thick & thin filaments together during contraction
Actin filaments: thin filaments
Made of contractile protein actin
Regulatory proteins prevent binding of myosin heads to actin
Anchored to the Z disc
I band only contains actin filaments

11. Z Line to Z Line called Sarcomere

12. Properties of Skeletal Muscle
Excitability/responsiveness
Receive and respond to stimuli
Contractility
Ability to shorten (forcibly) when adequately stimulated
Extensibility
Muscle cells can be stretched
Elasticity
Ability to recoil and resume their resting length after being stretched

13. Neuromuscular Junction
Must be stimulated by nerve impulses
One motor neuron (nerve cell) can stimulate a few muscle cells or hundreds of them
Motor unit: one motor neuron and all skeletal muscle cells it stimulates
Axon of neuron branches into axon terminals, each of which forms junctions with sarcolemma of different muscle cells
Neuromuscular junctions: contain vesicles filled with neurotransmitters
NTM that stimulates skeletal muscle cells: acetylcholine (ACh)
Synaptic cleft: gap between axon terminal and sarcolemma of muscle cell; filled with interstitial fluid

14. Neuromuscular Junction

15. Physiology of Muscle Contraction
When nerve impulse reaches axon terminals…
1. Calcium channels open and Ca2+ enters the terminal causing release of Ach
2. ACh diffuses across the synaptic cleft and attaches to receptors (membrane proteins) that are located in the sarcolemma of the muscle cell
4. Ach stimulates sarcolemma and causes depolarization, generating an action potential (more on that in the nervous system!)
5. Action potential spreads throughout the muscle cell and stimulates sarcoplasmic reticulum to release calcium ions into the cytoplasm
6. Calcium ions trigger binding of myosin to actin, initiating filament sliding
7. Acetylcholinesterase enzyme breaks down ACh (present on sarcolemma and in synaptic cleft).
Single nerve impulse produces only one contraction
Prevents continued contraction of the muscle cell in the absence of additional nerve impulses.

16. Sliding Filament Theory
Pages (fig 6.7 & 6.8)
Myosin heads attach to binding sites on the thin filaments when stimulated by nervous system (Calcium present)
Each cross bridge attaches and detaches (bend, break, & reform) several times during a contraction (using energy from ATP), generating tension that helps to pull the thin filaments toward the center of the sarcomere (form cross bridges further down actin filament) – power stroke
Myofilaments do not shorten – just slide past each other
Occurs simultaneously in sarcomeres throughout the muscle cell (cell shortens)
Attachment of myosin cross bridges to actin requires calcium ions
Takes a few thousandths of a second
animation

17. Sliding Filament Theory

18. State farm
link
Detailed animation

19. Muscle Response
Threshold stimulus: minimal stimulus needed to cause contraction
All-or-none response
Can be measured by a myogram (figure 6.9)

20. Electromyogram

21. Contraction of Skeletal Muscle as a Whole
Whole muscle contraction is through graded responses
different degrees of shortening throughout the whole muscle
Produced two ways:
Changing the frequency of muscle stimulation
Changing the number of muscle cells being stimulated at one time

22. Muscle Response to Increasingly Rapid Stimulation
Nerve impulses delivered to muscle at a very rapid rate (no chance for muscle to relax)
Effects of successive contractions are added together (summative)
Causes stronger & smoother contraction
Sustained contraction
Fused (complete) tetanus: contractions completely smooth and sustained
Unfused (incomplete) tetanus: up until the point of fused tetanus

23. Muscle Response to Stronger Stimuli
Force of muscle contraction mostly depends on how many cells are stimulated
when all motor units are active and all cells stimulated, muscle contraction is as strong as it can get
Muscle cells stimulated at the same time & entire muscle contracts
Motor units recruit other fibers
Link

24. Energy for Muscle Contraction
Muscle store a small amount of ATP (a few seconds’ worth) to get going
ATP only energy source can be used directly to power muscle activity & must be regenerated continuously if contraction is to continue
ATP regeneration catalyzed by ATPase
Three pathways for ATP regeneration:
Direct phosphorylation of ADP by creatine phosphate
Aerobic respiration
Anaerobic glycolysis & lactic acid formation
Only 25% of energy is used – rest released as heat!

25. Creatine Phosphate
High energy molecule found in muscle fibers but not other cell types
Regenerates ATP in a fraction of a second by transferring a phosphate group to ADP
CP supplies exhausted in less than 15 seconds

26. Aerobic Respiration 95% of ATP used for muscle activity
Oxidative phosphorylation: occurs in mitochondria, metabolic pathways that use oxygen
Glucose broken down completely to carbon dioxide & water, energy released as bonds are broken  energy captured in ATP molecules
Generates a large amount of ATP
Slow and requires continuous delivery of oxygen and nutrient fuels to muscle to keep it going

27. Anaerobic Glycolysis & Lactic Acid Fermentation
If oxygen & glucose delivery is inadequate (intense muscle activity), glycolysis moves into lactic acid fermentation instead of oxidative phosphorylation
Only 5% as much ATP produced without oxygen
2.5 times faster and provides most of ATP needed for seconds of strenuous activity
Lactic acid accumulates and produces muscle soreness

28. Muscle Fatigue & Oxygen Deficit
Muscle fatigue: unable to contract even though being stimulated
Oxygen deficit occurs after prolonged muscle activity, causing fatigue
Work that a muscle can do and how long without fatigue depends on blood supply
Without adequate oxygen, lactic acid accumulates and ATP supply runs low, which leads to fatigue
i.e. marathon runners

29. Types of Muscle Contractions
Isotonic contractions: myofilaments slide past each other, muscle shortens, movement occurs
Isometric contractions: muscles do not shorten, tension increases in muscle but myofilaments do not slide past each other
Movement pitted against an immoveable object
Muscle tone: continuous partial contractions that occur involuntarily due to nervous stimulation to keep a muscle firm, healthy, and ready for action (controlled by gene called myostatin)
If no longer stimulated in this way, loses tone and muscle is flaccid and begins to atrophy
link

31. Muscle Movement “Golden Rules” (Table 6.2, page 197)
All skeletal muscles cross at least one joint (with few exceptions)
Bulk of skeletal muscle lies proximal to joint crossed
All skeletal muscles have at least two attachments: the origin & the insertion
Skeletal muscles can only pull; they can never push
During contraction, a skeletal muscle insertion moves toward the origin

32. Muscle Movement
All skeletal muscles are attached to bone or to other connective tissue structures at no fewer than two points
Origin: attached to the immovable or less movable bone
Insertion: attached to the movable bone, and when muscle contracts, moves toward the origin
Some muscles have interchangeable origins & insertions or multiple origins/insertions (i.e. biceps brachii)
body movement occurs when muscles contract across joints

33. Biceps Brachii Fig 6.12, page 197 2 origins at shoulder
Insertion across elbow – attaches to ulna
Belly

34. Interactions of Skeletal Muscles
Muscles function in groups
Groups of muscles that produce opposite movements lie on opposite sides of a joint
Prime mover: muscle that has major responsibility for causing a movement
Antagonists: muscles that oppose or reverse a movement
Muscles can be both prime movers and antagonists (i.e. biceps & triceps)
Synergists: help prime movers by producing same movement or reducing undesirable movements (stabilize joints)

35. Interactions of Muscles

36. Putting it all together:
Physics!!

38. link

39. Naming Skeletal Muscles
Direction of the muscle fibers
External obliques
Relative size of the muscle
Pectoralis major
Location of the muscle’s
origin and insertion
Sternocleidomastoid
Shape of the muscle
deltoid
Action of the muscle
Extensor digitorum

40. Direction of Muscle Fibers
External oblique
oblique= at a slant
Rectus abdominus
Rectus = straight (parallel)
Transversus abdominus
transversus= straight (perpendicular)
Using the midline of the body or axis of a long bone

41. Relative Size of Muscle
Major/minor
Vastus
Long; covers a lot of area; big
Maximus/minimus
Medius
Longus
Brevis= short

42. Location Frontalis Temporalis Tibialis anterior Biceps femoris
(not the same as the biceps
brachii in your arm!)

43. Action of the Muscle
Adductor
Extensor digitorum

44. Number of Attachments Biceps brachii
Biceps femoris
Triceps brachii
Also give location (brachial; femoral)

45. Arrangement of Fascicles
Determines range of motion and power
Circular: concentric rings (sphincters)
Ex. Orbicularis muscles (eyes & mouth)
Convergent: fascicles converge toward a single insertion tendon (triangular or fan shaped)
Ex. Pectoralis major
Parallel: length of fascilces run parallel to the long axis of muscle (straplike)
Fusiform: spindle-shaped with expanded “belly”
Ex. Biceps brachii
Pennate: short fascicles attach obliquely to central tendon
Unipennate (insert into one side of tendon)
Bipennate & multipennate (most powerful)

46. Figure 6.15

47. Fascicle arrangement determines range of motion and power
Longer and parallel provide much ROM/little power
Shorter, more plentiful provide much power/little ROM

49. Circular
Orbicularis oculi
Orbicularis oris

50. Convergent
Pectoralis Major

51. Parallel
Sternocleidomastoid
Sartorius

52. Fusiform
Biceps brachii
Tensor fasciae lata
Semitendinosus

53. Unipennate
Extensor digitorum longus

54. Bipennate
Rectus femoris

55. Multipennate
Deltoids

56. Want a good workout? Try gardening!

57. rap
Arm
NFL