1. Headings Vocabulary Important Info
Muscular System
Headings
Vocabulary
Important Info

2. 3 Types of Muscle Tissue Skeletal muscle Cardiac muscle Smooth muscle
attaches to bone, skin or fascia
striated with light & dark bands visible with microscope
voluntary control of contraction & relaxation
Cardiac muscle
striated in appearance
involuntary control
autorhythmic because of built in pacemaker
Smooth muscle
attached to hair follicles in skin
in walls of hollow organs – blood vessels & GI
nonstriated in appearance
involuntary
***fascia are dense regular connective tissues, containing closely packed bundles of collagen-it binds like plastic wrap***

3. Functions of Muscle Tissue
Producing body movements
Stabilizing body positions
Regulating organ volumes
bands of smooth muscle called sphincters
Movement of substances within body
blood, lymph (colorless fluid containing white blood cells), urine, air, food and fluids, sperm
Producing heat
involuntary contractions of skeletal muscle (shivering)

4. Properties of Muscle Tissue
Excitability
respond to chemicals released from nerve cells
Conductivity
ability to propagate electrical signals over membrane
Contractility
ability to shorten and generate force
Extensibility
ability to be stretched without damaging the tissue
Elasticity
ability to return to original shape after being stretched

5. Skeletal Muscle -- Connective Tissue
Superficial Fascia is loose connective tissue & fat underlying the skin
Deep Fascia = dense irregular connective tissue around muscle
Connective tissue components of the muscle include
Epimysium = surrounds the whole muscle
Perimysium = surrounds bundles (fascicles) of muscle cells
Endomysium = separates individual muscle cells
All these connective tissue layers extend beyond the muscle belly to form the tendon

6. Connective Tissue Components

7. Nerve and Blood Supply
Each skeletal muscle is supplied by a nerve, artery and two veins.
Each motor neuron supplies multiple muscle cells (neuromuscular junction)
Each muscle cell is supplied by one motor neuron terminal branch and is in contact with one or two capillaries.
nerve fibers & capillaries are found in the endomysium b/t individual cells

9. Fusion of Myoblasts into Muscle Fibers
Every mature muscle cell developed from 100 myoblasts that fuse together in the fetus. (multinucleated)
Mature muscle cells can not divide
Muscle growth is a result of cellular enlargement & not cell division (Mitosis)
Satellite cells retain the ability to regenerate new cells
Evidence suggesting that these cells are capable of fusing with existing myofibers to facilitate growth and repair.

10. Muscle Fiber or Myofibers
Muscle cells are long, cylindrical & multinucleated
Sarcolemma = muscle cell membrane
Sarcoplasm filled with tiny threads called myofibrils & myoglobin (red-colored, oxygen-binding protein)

11. Transverse Tubules T (transverse) tubules: elongated tube
Found at the end of each A band-I band junction
filled with extracellular fluid
carry muscle action potentials down into cell
Mitochondria lie in rows throughout the cell
near the muscle proteins that use ATP during contraction

12. Myofibrils & Myofilaments
Muscle fibers are filled with threads called myofibrils separated by SR (sarcoplasmic reticulum)
Myofilaments (thick & thin filaments) are the contractile proteins of muscle

13. Sarcoplasmic Reticulum (SR)
System of tubular sacs like smooth ER in nonmuscle cells
Stores Ca+2 in relaxed muscle
Release of Ca+2 triggers muscle contraction

14. Filaments and the Sarcomere
Thick and Thin filaments overlap each other in a pattern that creates striations
light I bands and dark A bands
The I band region contains only thin filaments.
They are arranged in compartments called sarcomeres, separated by Z discs.
In the overlap region, six thin filaments surround each thick filament
Thick
Thin
I Band

15. Thick & Thin Myofilaments
Supporting proteins (M line, titin and Z disc help anchor the thick and thin filaments in place)

16. Overlap of Thick & Thin Myofilaments within a Myofibril
Dark(A) & light(I) bands visible with an electron microscope

17. The Proteins of Muscle Myofibrils are built of 3 kinds of protein
contractile proteins
myosin and actin
regulatory proteins which turn contraction on & off
troponin and tropomyosin
structural proteins which provide proper alignment, elasticity and extensibility
titin, myomesin, nebulin & dystrophin

18. The Proteins of Muscle -- Myosin
Thick filaments are composed of myosin
each molecule resembles two golf clubs twisted together
myosin heads (Cross Bridges) extend toward the thin filaments
Held in place by the M line proteins.

19. The Proteins of Muscle -- Actin
Thin filaments are made of actin, troponin, & tropomyosin
The myosin-binding site on each actin molecule is covered by tropomyosin in relaxed muscle
The thin filaments are held in place by Z lines.
From one Z line to the next is a sarcomere.

20. The Proteins of Muscle -- Titin
Titan anchors thick filament to the M line and the Z disc.
The portion of the molecule between the Z disc and the end of the thick filament can stretch to 4 times its resting length and spring back unharmed.
Role in recovery of the muscle from being stretched.

21. Other Structural Proteins
The M line (myomesin) connects to titin and adjacent thick filaments.
Nebulin, an inelastic protein helps align the thin filaments.
Dystrophin links thin filaments to sarcolemma and transmits the tension generated to the tendon.

22. Sliding Filament Mechanism Of Contraction
Myosin cross bridges pull on thin filaments
Thin filaments slide inward
Z Discs come toward each other
Sarcomeres shorten…The muscle fiber shortens…The muscle shortens
Notice : Thick & thin filaments do not change in length

23. How Does Contraction Begin?
Nerve impulse reaches an axon terminal & synaptic vesicles release acetylcholine (ACh)
ACh diffuses to receptors on the sarcolemma & Na+ channels open and Na+ rushes into the cell
A muscle action potential spreads over sarcolemma and down into the transverse tubules
SR releases Ca+2 into the sarcoplasm
Ca+2 binds to troponin & causes troponin-tropomyosin complex to move & reveal myosin binding sites on actin--the contraction cycle begins

24. Contraction Cycle
Repeating sequence of events that cause the thick & thin filaments to move past each other.
4 steps to contraction cycle
ATP hydrolysis
attachment of myosin to actin to form crossbridges
power stroke
detachment of myosin from actin
Cycle keeps repeating as long as there is ATP available & high Ca+2 level near thin filament

25. Steps in the Contraction Cycle
Notice how the myosin head attaches and pulls on the thin filament with the energy released from ATP

27. ATP and Myosin Myosin heads are activated by ATP
Activated heads attach to actin & pull (power stroke)
ADP is released. (ATP released P & ADP & energy)
Thin filaments slide past the thick filaments
ATP binds to myosin head & detaches it from actin
All of these steps repeat over and over
if ATP is available
Ca+ level near the troponin-tropomyosin complex is high

28. Relaxation
Acetylcholinesterase (AChE) breaks down ACh within the synaptic cleft
Muscle action potential ceases
Ca+2 release channels close
Active transport pumps Ca2+ back into storage in the sarcoplasmic reticulum
Calcium-binding protein (calsequestrin) helps hold Ca+2 in SR (Ca+2 concentration 10,000 times higher than in cytosol)
Tropomyosin-troponin complex recovers binding site on the actin

29. Neuromuscular Junction (NMJ) or Synapse
NMJ = neuromuscular junction
end of axon nears the surface of a muscle fiber at its motor end plate region (remain separated by synaptic cleft or gap)

30. Structures of NMJ Region
Synaptic end bulbs are swellings of axon terminals
End bulbs contain synaptic vesicles filled with acetylcholine (ACh)
Motor end plate membrane contains 30 million ACh receptors.

31. Events Occurring After a Nerve Signal
Arrival of nerve impulse at nerve terminal causes release of ACh from synaptic vesicles
ACh binds to receptors on muscle motor end plate opening the gated ion channels so that Na+ can rush into the muscle cell
Inside of muscle cell becomes more positive, triggering a muscle action potential that travels over the cell and down the T tubules
The release of Ca+2 from the SR is triggered and the muscle cell will shorten & generate force
Acetylcholinesterase breaks down the ACh attached to the receptors on the motor end plate so the muscle action potential will cease and the muscle cell will relax.

32. Muscle Metabolism Production of ATP in Muscle Fibers
Muscle uses ATP at a great rate when active
Sarcoplasmic ATP only lasts for few seconds
3 sources of ATP production within muscle
creatine phosphate
anaerobic cellular respiration
aerobic cellular respiration

33. Creatine (Amino Acid) Phosphate
Produced in liver, pancreas & kidneys transported to muscles through bloodstream
Found naturally in some foods, like red meat/fish, but cooking destroys it
Excess ATP within resting muscle used to form creatine phosphate
Creatine phosphate 3-6 times more plentiful than ATP within muscle
Essential storehouse for energy
Regenerates ATP (Creatine phosphate + ADP  Creatine + ATP)
Its quick breakdown provides energy for creation of ATP
Sustains maximal contraction for 15 sec (used for 100 meter dash)
Athletes tried creatine supplementation
gain muscle mass but shut down bodies own synthesis of creatine (safety?)
benefit limited to anaerobic sports (none for endurance athletes)

34. Anaerobic Cellular Respiration
ATP produced from glucose breakdown into pyruvic acid during glycolysis
if no O₂ present:
Pyruvic converted to lactic acid which diffuses into the blood
Glycolysis can continue anaerobically to provide ATP for 30 to 40 seconds of maximal activity (200 meter race)

35. Aerobic Cellular Respiration
ATP for any activity lasting over 30 seconds
with O₂ present, pyruvic acid enters the mitochondria to generate ATP, water and heat
fatty acids and amino acids can also be used by the mitochondria
Provides 90% of ATP energy if activity lasts more than 10 minutes

36. Muscle Fatigue Inability to contract after prolonged activity
central fatigue is feeling of tiredness and a desire to stop (protective mechanism)
depletion of creatine phosphate
decline of Ca+2 within the sarcoplasm
Factors that contribute to muscle fatigue
insufficient oxygen or glycogen
buildup of lactic acid and ADP
insufficient release of acetylcholine from motor neurons

38. Oxygen Consumption after Exercise
Muscle tissue has two sources of oxygen.
diffuses in from the blood
released by myoglobin inside muscle fibers
Aerobic system requires O₂ to produce ATP needed for prolonged activity
increased breathing effort during exercise
Recovery oxygen uptake
elevated oxygen use after exercise (oxygen debt)
lactic acid is converted back to pyruvic acid
elevated body temperature means all reactions faster

39. The Motor Unit
Motor unit = one somatic motor neuron & all the skeletal muscle cells (fibers) it stimulates
muscle fibers normally scattered throughout belly of muscle
One nerve cell supplies on average 150 muscle cells that all contract in unison.
Total strength of a contraction depends on how many motor units are activated & how large the motor units are

40. Twitch Contraction
Brief contraction of all fibers in a motor unit in response to:
single action potential in its motor neuron
electrical stimulation of the neuron or muscle fibers
Myogram = graph of a twitch contraction
the action potential lasts 1-2 msec
the twitch contraction lasts from 20 to 200 msec

41. Myogram of a Twitch Contraction

42. Parts of a Twitch Contraction
Latent Period--2msec
Ca+2 is being released from SR
slack is being removed from elastic components
Contraction Period
10 to 100 msec
filaments slide past each other
Relaxation Period
active transport of Ca+2 into SR
Refractory Period
muscle can not respond and has lost its excitability
5 msec for skeletal & 300 msec for cardiac muscle

43. Wave Summation
If second stimulation applied after the refractory period but before complete muscle relaxation---second contraction is stronger than first

44. Force of 2nd contraction is easily added to first.
Elastic elements remain partially contracted and do not delay beginning of next contraction.
Contraction without relaxation - tetanus

45. Muscle Tone
Involuntary contraction of a small number of motor units (alternately active and inactive in a constantly shifting pattern)
keeps muscles firm even though relaxed
does not produce movement
Essential for maintaining posture (head upright)
Important in maintaining blood pressure
tone of smooth muscles in walls of blood vessels

46. Atrophy & Hypertrophy Atrophy wasting away of muscles
caused by disuse (Disuse Atrophy) or severing of the nerve supply (Denervation Atrophy)
transition to connective tissue can not be reversed

47. Hypertrophy
increase in diameter of muscle fibers resulting from very forceful, repetitive muscular activity & increase in myofibrils, SR & mitochondria
Sarcoplasmic Hypertrophy: leads to larger muscles – Non-Functional Muscle (little force)
increased sarcoplasm & mitochondria & non- contractile proteins that do not directly contribute to muscular force
triggered by increasing repetitions
Bodybuilders use 10 – 15 rep range
leads to quick and massive increases in size

48. Myofibrillar Hypertrophy: which builds athletic strength- Functional Muscle (greater for production)
Actin & Myosin contractile proteins increase in #
adds to muscular strength
small increase in size of muscle
Low rep/heavy weight
Usually sets in 1 – 3 rep range
Use massive weights to build strength
For little muscle growth:
3 – 6 reps each set using small weights

49. Anabolic Steroids Similar to testosterone
Increases muscle size, strength, and endurance
Many very serious side effects
liver cancer
kidney damage
heart disease
mood swings
facial hair & voice deepening in females
atrophy of testicles & baldness in males

50. Aging and Muscle Tissue
Skeletal muscle starts to be replaced by fat beginning at 30
“use it or lose it”
Slowing of reflexes & decrease in maximal strength
Change in fiber type to slow oxidative fibers may be due to lack of use or may be result of aging

51. Anatomy of Cardiac Muscle
Striated , short, quadrangular-shaped, branching fibers
Single centrally located nucleus
Cells connected by intercalated discs with gap junctions
Same arrangement of thick & thin filaments as skeletal

52. Cardiac versus Skeletal Muscle
More sarcoplasm and mitochondria
Larger transverse tubules located at Z discs, rather than at A-l band junctions
Less well-developed SR
Limited intracellular Ca+2 reserves
more Ca+2 enters cell from extracellular fluid during contraction
Prolonged delivery of Ca+2 to sarcoplasm, produces a contraction that last times longer than in skeletal muscle

53. Appearance of Cardiac Muscle
Striated muscle containing thick & thin filaments
T tubules located at Z discs & less SR

54. Physiology of Cardiac Muscle
Autorhythmic cells
contract without stimulation
Contracts 75 times per min & needs lots O2
Larger mitochondria generate ATP aerobically
Sustained contraction possible due to slow Ca+2 delivery
Ca+2 channels to the extracellular fluid stay open

55. Two Types of Smooth Muscle
Visceral (single-unit)
in the walls of hollow viscera & small BV
autorhythmic
gap junctions cause fibers to contract in unison
Multiunit
individual fibers with own motor neuron ending
found in large arteries, large airways, arrector pili muscles,iris & ciliary body

56. Microscopic Anatomy of Smooth Muscle
Small, involuntary muscle cell -- tapering at ends
Single, oval, centrally located nucleus
Lack T tubules & have little SR for Ca+2 storage

57. Microscopic Anatomy of Smooth Muscle
Thick & thin myofilaments not orderly arranged so lacks sarcomeres
Sliding of thick & thin filaments generates tension
Transferred to intermediate filaments & dense bodies attached to sarcolemma
Muscle fiber contracts and twists into a helix as it shortens -- relaxes by untwisting

58. Physiology of Smooth Muscle
Contraction starts slowly & lasts longer
no transverse tubules & very little SR
Ca+2 must flows in from outside
Calmodulin replaces troponin
Ca+2 binds to calmodulin turning on an enzyme (myosin light chain kinase) that phosphorylates the myosin head so that contraction can occur
enzyme works slowly, slowing contraction

59. Smooth Muscle Tone Ca+2 moves slowly out of the cell
delaying relaxation and providing for state of continued partial contraction
sustained long-term
Useful for maintaining blood pressure or a steady pressure on the contents of GI tract

60. Regulation of Contraction
Regulation of contraction due to:
nerve signals from autonomic nervous system
changes in local conditions (pH, O2, CO2, temperature & ionic concentrations)
hormones (epinephrine -- relaxes muscle in airways & some blood vessels)
Stress-relaxation response
when stretched, initially contracts & then tension decreases to what is needed
stretch hollow organs as they fill & yet pressure remains fairly constant
when empties, muscle rebounds & walls firm up

61. Regeneration of Muscle
Skeletal muscle fibers cannot divide after 1st year
growth is enlargement of existing cells
repair
satellite cells & bone marrow produce some new cells
if not enough numbers---fibrosis occurs most often
Cardiac muscle fibers cannot divide or regenerate
all healing is done by fibrosis (scar formation)
Smooth muscle fibers (regeneration is possible)
cells can grow in size (hypertrophy)
some cells (uterus) can divide (hyperplasia)
new fibers can form from stem cells in BV walls

62. Developmental Anatomy of the Muscular System
Develops from mesoderm
Somite formation
blocks of mesoderm give rise to vertebrae and skeletal muscles of the back
Muscles of head & limbs develop from general mesoderm

63. Skeletal System Actions
Skeletal muscle is responsible for body movement.
- Origin – attached to immovable or fixed point
of joint
- Insertion – attached to movable point of joint
Muscle contraction moves insertion toward origin.
Both ends of muscle are connected to bone by tendons.

64. Coordination Within Muscle Groups
Most movement is the result of several muscle working at the same time
Most muscles are arranged in opposing pairs at joints
prime mover or agonist contracts to cause the desired action
antagonist stretches and yields to prime mover
synergists contract to stabilize nearby joints
fixators stabilize the origin of the prime mover
scapula held steady so deltoid can raise arm

65. Isotonic and Isometric Contraction
Isotonic contractions = a load is moved
Isometric contraction = no movement occurs
tension is generated without muscle shortening
maintaining posture & supports objects in a fixed position

66. First - Class Lever
Can produce mechanical advantage or not depending on location of effort & resistance
if effort is further from fulcrum than resistance, then a strong resistance can be moved
Head resting on vertebral column
weight of face is the resistance
joint between skull & atlas is fulcrum
posterior neck muscles provide effort

67. Second - Class Lever Similar to a wheelbarrow
Always produce mechanical advantage
resistance is always closer to fulcrum than the effort
Sacrifice of speed for force
Raising up on your toes
resistance is body weight
fulcrum is ball of foot
effort is contraction of calf muscles which pull heel up off of floor

68. Third - Class Lever Most common levers in the body
Always produce a mechanical disadvantage
effort is always closer to fulcrum than resistance
Favors speed and range of motion over force
Flexor muscles at the elbow
resistance is weight in hand
fulcrum is elbow joint
effort is contraction of biceps brachii muscle

69. Myasthenia Gravis
Progressive autoimmune disorder that blocks the ACh receptors at the neuromuscular junction
The more receptors are damaged the weaker the muscle.
More common in women 20 to 40 with possible line to thymus gland tumors
Begins with double vision & swallowing difficulties & progresses to paralysis of respiratory muscles
Treatment includes steroids that reduce antibodies that bind to ACh receptors and inhibitors of acetylcholinesterase

70. Muscular Dystrophies Inherited, muscle-destroying diseases
Sarcolemma tears during muscle contraction
Mutated gene is on X chromosome so problem is with males almost exclusively
Appears by age 5 in males and by 12 may be unable to walk
Degeneration of individual muscle fibers produces atrophy of the skeletal muscle
Gene therapy is hoped for with the most common form = Duchenne muscular dystrophy

71. Abnormal Contractions
Spasm = involuntary contraction of single muscle
Cramp = a painful spasm
Tic = involuntary twitching of muscles normally under voluntary control--eyelid or facial muscles
Tremor = rhythmic, involuntary contraction of opposing muscle groups
Fasciculation = involuntary, brief twitch of a motor unit visible under the skin

72. Tenosynovitis
Inflammation of tendon and associated connective tissues at certain joints
wrist, elbows and shoulder commonly affected
Pain associated with movement
Causes
trauma, strain or excessive exercise

74. Fascicle Arrangements
A contracting muscle shortens to about 70% of its length
Fascicular arrangement represents a compromise between force of contraction (power) and range of motion
muscles with longer fibers have a greater range of motion
a short fiber can contract as forcefully as a long one.

75. How Skeletal Muscle are Named
Direction the muscle fibers run
Size, shape, action, number of origins or locations
Examples:
triceps brachii sites of origin
quadratus femoris – square shape
serratus anterior – saw-toothed edge

76. Exercise-Induced Muscle Damage
Intense exercise can cause muscle damage
electron micrographs reveal torn sarcolemma's, damaged myofibrils and disrupted Z discs
increased blood levels of myoglobin & creatine phosphate found only inside muscle cells

77. Delayed Onset Muscle Soreness (DOMS)
12 to 48 Hours after strenuous exercise
stiffness, tenderness and swelling due to microscopic cell damage
As you weight train, you cause micro-trauma, or damage to the small fibers of your muscles, which are composed of proteins.
It is the repair to these micro-trauma (usually by satellite cells) that result in muscle growth in addition to added proteins
The harder/longer you train, the more damage you do which means you need to eat possibly twice as much protein as a sedentary individual.
As muscles adapt to exercises, soreness tends to decrease.

78. Pharmacology of the NMJ
Botulinum toxin blocks release of neurotransmitter at the NMJ so muscle contraction can not occur
bacteria found in improperly canned food
death occurs from paralysis of the diaphragm

79. Curare (plant poison from poison arrows)
causes muscle paralysis by blocking the ACh receptors
used to relax muscle during surgery
Neostigmine (anticholinesterase agent)
blocks removal of ACh from receptors so strengthens weak muscle contractions of myasthenia gravis
also an antidote for curare after surgery is finished
Myasthenia gravis occurs when the immune system makes antibodies that damage or block many of the muscle's acetylcholine (ACh) receptors on the surface of muscle cells. This prevents ACh from binding to the damaged receptors and acting on the muscle, which reduces muscle contractions, leading to weakness and fatigue

80. Classification of Muscle Fibers
Slow oxidative (slow-twitch)
red in color (lots of mitochondria, myoglobin & blood vessels)
prolonged, sustained contractions for maintaining posture/marathon
Fast oxidative-glycolytic (fast-twitch A)-Run/Sprint
red in color (lots of mitochondria, myoglobin & blood vessels)
split ATP at very fast rate; used for walking/sprint/swing a bat
Fast glycolytic (fast-twitch B)-Endurance
white in color (few mitochondria & BV, low myoglobin)
anaerobic movements for short duration; used for weight-lifting

81. Fiber Types within a Whole Muscle
Most muscles contain a mixture of all three fiber types
Proportions vary with the usual action of the muscle
neck, back and leg muscles have a higher proportion of postural, slow oxidative fibers
shoulder and arm muscles have a higher proportion of fast glycolytic fibers
All fibers of any one motor unit are same.
Different fibers are recruited as needed.

82. Rigor Mortis Muscular rigidity that begins 3-4 hours after death
lasts about 24 hours
After death, Ca+2 ions leak out of the SR and allow myosin heads to bind to actin
Since ATP synthesis has ceased, crossbridges cannot detach from actin until proteolytic enzymes begin to digest the decomposing cells.

83. Lever Systems and Leverage
Muscle acts on rigid rod (bone) that moves around a fixed point called a fulcrum
Resistance is weight of body part & perhaps an object
Effort or load is work done by muscle contraction
Mechanical advantage
the muscle whose attachment is farther from the joint will produce the most force
the muscle attaching closer to the joint has the greater range of motion and the faster the speed it can produce