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Anatomy & Physiology > Chapter #9: Muscles & Muscle Tissue > Flashcards

Chapter #9: Muscles & Muscle Tissue Flashcards

1
Q

Muscle Functions

A
  1. Movement
  2. Body posture & body position
  3. Joint stability
  4. Maintaining body temperature
  5. Excitability
  6. Contractility
  7. Extensibility
  8. Elasticity
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2
Q

Movement

A

voluntary and involuntary

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3
Q

Body posture & body position

A

Muscles work to hold us up against gravity

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4
Q

Joint Stability

A

Muscles & tendons reinforce joints

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5
Q

Maintaining body temperature

A

Muscle contraction produces heat

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6
Q

Excitability

A

Membrane potential changes in response to stimulus

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7
Q

Contractility

A

Muscle cells shorten

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8
Q

Extensibility

A

Muscles cells can lengthen/stretch

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9
Q

Elasticity

A

Healthy muscle cells return to their original shape

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10
Q

Types of muscle tissue

A
  1. Skeletal muscle tissue
  2. Smooth muscle tissue
  3. Cardiac muscle tissue
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11
Q

Skeletal muscle tissue

A

-Voluntary muscle tissue
-Function: movement of body parts

-Striated & multinucleate

-Attaches to & uses skeleton

-Creates the most force
-But: needs the most rest

-Adaptable

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12
Q

Smooth muscle tissue

A

-Involuntary muscle tissue
-Function: moves fluids & substances through body

-No striations
-Uninucleate

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13
Q

Cardiac muscle tissue

A

-Involuntary muscle tissue
-Function: moves blood through body
*Rate of contraction set by pacemaker cells

-Striated
-Uninucleate

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14
Q

Gross Anatomy of Skeletal muscle tissue

A

-innervation
-vascularization
-connective tissue sheaths

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15
Q

Innervation

A

-Each muscle receives 1 motor nerve
-Function: nerve ending controls activity
-Motor neuron stimulates muscle fibers to contract

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16
Q

What neurotransmitter is released by motor neurons?

A

acetylcholine (always stimulatory)

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17
Q

Vascularization

A

-Each muscle receives 1 artery, 1+ vein
-Functions: Bring in nutrients, remove waste

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18
Q

Connective Tissue Sheaths

A

-Function: supports muscle, holds muscle together

-Layers:
-Endomysium: innermost layer
-Surrounds individual muscle fibers

 -Perimysium: middle layer
       -Discrete bundles of muscle fibers grouped together: form fascicles

 -Epimysium: outermost layer
      -Surrounds entire muscle
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19
Q

Skeletal muscle attachments

A

-For skeletal muscle to produce movement, it must attach to bone (or another tough structure)
-Why? Our muscles use our bones like levers
-When a muscle contracts, it pulls (or pushes) on a bone to produce movement

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20
Q

Direct vs. Indirect attachment of skeletal muscle attachments

A

-Direct: epimysium of muscle fuses directly to bone (or cartilage)

-Indirect: involves tendons
-Tendon: a band of dense fibrous connective tissue that connects a muscle to a bone

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21
Q

Is indirect or direct attachment of skeletal muscle attachment more common?

A

indirect because tendons are stronger and thicker

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22
Q

2 points of attachment for a muscle

A

1) Origin: where the muscle attaches to a less movable bone
-Always proximal
-Ex: biceps brachii: long head = lip of glenoid fossa, short head = coracoid process

2) Insertion: where the muscle attaches to a movable bone
-Always distal
-Ex: biceps brachii: radial tubersity

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23
Q

Microanatomy of skeletal muscles

A

Skeletal muscle cells (myocytes, muscle fibers) are among largest and longest cells in the body

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24
Q

Important terminology for skeletal muscle microanatomy

A

1) Sarcolemma
2) Sarcopla
3) Myofilaments
4) Myofibrils

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25
Q

Sarcolemma

A

plasma membrane of muscle fibers

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26
Q

Sarcoplasm

A

-cytoplasm of muscle fibers
-Contain high numbers of
A) Glycosomes: organelles that store glycogen
-Importance: glycogen is a polysaccharide that is converted to glucose for ATP production in skeletal muscle
B) Myoglobin: red pigment organelle that stores oxygen
-Importance: oxygen is needed for ATP production

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27
Q

Myofilaments

A

-protein filaments in muscle tissue

-Types of contractile myofilaments:
A) Thick filament (myosin)

B) Thin filament (actin)

-Function: actin and myosin interact during muscle contraction

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28
Q

Myosin FIlaments

A

-Composed of 6 chains
-4 light chains

-2 heavy chains
     -Myosin head found at end of each heavy chain
          -Each myosin head has 2 binding sites: 1 for ATP, 1 for actin

-Importance: myosin head uses ATP to link two types of myofilaments during contraction

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29
Q

Actin filaments

A

-Chains of G actin proteins with myosin binding sites

-Function: myosin head binds to the myosin binding site of actin during muscle contraction

     -Regulatory proteins of actin control if/when myosin head can bind
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30
Q

2 regulatory proteins associated with actin filaments

A

1) Tropomyosin: arranged along length of thin filament

Function: blocks myosin binding sites on actin filament when muscle is relaxed

2) Troponin: globular protein associated with tropomyosin

Function: binds tropomyosin to position it on the actin filament

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31
Q

Myofibrils

A

-rod-like organelles of muscle cells
-Myofibrils are made up of bands of myofilaments
-Myofilaments overlap in some regions of the myofibril to produce dark bands
-This is what creates striations of skeletal muscle!

-Each muscle fiber has several myofibrils

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32
Q

Myofibrils composed of alternating A bands and I bands

A

1) A band: region of myofibril where actin and myosin filaments overlap
-H zone at the center of A band has only myosin filaments

2) I band: region of myofibril with only actin filaments
-Z disc at center holds the actin filaments in place

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33
Q

What does an A band and I band create?

A

Sarcomere

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34
Q

Sarcomeres

A

-A sarcomere is the region of a myofibril found between 2 successive Z discs

-Importance: the sarcomere is the smallest contractile unit of skeletal muscle tissue

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35
Q

What part of the A band and I band make up a single sarcomere?

A

1 A band and half an I band

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36
Q

What happens to a muscle when the sarcomere shortens?

A

the myofibril becomes shorter, so the muscles cell becomes shorter, so the entire muscle becomes shorter

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37
Q

Other intracellular structures that regulate muscle contraction

A

1) T-Tubules
2) Sarcoplasmic reticulum

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38
Q

T-Tubules

A

-extensions of the sarcolemma that wrap around deeper myofibrils

-Function: increase surface area of muscle fiber sarcolemma 
    -Importance: changes in membrane potential can reach myofibrils not in direct contact with sarcolemma
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39
Q

Sarcoplasmic reticulum

A

-smooth endoplasmic reticulum of muscle
-Highly branched, wraps around myofibrils

-Form terminal cisterns around T-tubules
     -Function: stores and releases intracellular Ca2+ for muscle relaxation & contraction

      -Notice: 2 terminal cisterns surround 1 t-tubule to form a triad
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40
Q

The Neuromuscular Junction

A

-Definition: site of synapse between a somatic motor neuron and a muscle fiber
-Neurotransmitter released: Acetylcholine (ACh)

-Sarcolemma at synaptic cleft folded to form junctional folds
-Function: folds increase surface area of muscle fiber sarcolemma

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41
Q

What effect does acetylcholine have on a muscle fiber?

A

Always stimulatory, always causes contraction

42
Q

Why is it advantageous for the sarcolemma at the synaptic cleft to form junction folds?

A

increases the likelihood that receptor can bind with acetylcholine since surface area is increased

43
Q

For stimulation of muscle fiber to occur, to following steps must take place

A

1) Events at the neuromuscular junction
2) Generation of action potential across sarcolemma
3) Excitation-Contraction Coupling
4) Cross Bridge Formation & Muscle Contraction

44
Q

Step 1 for stimulation of muscle fiber: Events at the neuromuscular junction

A

-transmission of action potential

-Result: ACh is released & binds to chemically-gated ion channels on the sarcolemma

45
Q

Step 2 for stimulation of muscle fiber: Generation of action potential across sarcolemma

A

-ACh binds to and opens ion channels on sarcolemma to create end plate potential (EPP)
-EPP is a graded potential specific to muscle tissue

 -EPP depolarizes sarcolemma
      -If strong enough: action potential generated on sarcolemma
46
Q

Step 3 for stimulation of muscle fiber: Excitation-Contraction Coupling

A

-Occurs when action potential spreads from sarcolemma to T-tubules

-When action potential arrives at T-tubules: voltage-gated proteins in T-tubules change shape
-When T-tubule proteins change shapeCa2+ channels in terminal cistern forced open

-Result: Ca2+ released from sarcoplasmic reticulum & flows into cytosol of muscle fiber
47
Q

Step 4 for stimulation of muscle fiber: Cross Bridge Formation & Muscle Contraction

A

-Once Ca2+ enters cytosolinteraction between actin and myosin filaments can begin
-Cross bridge: the attachment of myosin to actin

-The Process of Cross Bridge Formation:
A) Ca2+ binds troponintroponin changes shape

B) Change in troponin shape causes tropomyosin to roll to the side

C) When tropomyosin is movedmyosin binding site on actin is exposed
 -Myosin head will bind to actin binding site with use of ATP

D) Myosin head splits ATP into ADP + Pi 
     -This allows myosin head to bind to actin

E) ADP + Pi is released from myosin head, causing the myosin head to bend
   -Effect: myosin head “pulls” actin filament
   -This is called the power stroke

F) Myosin head binds to another ATP: myosin head detaches from actin binding site

G) The myosin head binds to a different actin binding site

-Steps D-G repeat until muscle contraction ends or ATP/Ca2+ run short

48
Q

Ending cross-bridge formation & muscle contraction

A

-Motor impulses no longer sent to muscle fiber
-Action potential to muscle fiber ends

-Ca2+ is returned to sarcoplasmic reticulum

-When Ca2+ levels in sarcoplasm drop, it can no longer bind to troponin

-Troponin returns to original shape
-Result: Tropomyosin movescovers actin binding sites

49
Q

Sliding Filament Model of Contraction

A

-During contraction, actin filaments “slide” over myosin filaments
-Why? Myosin heads form & break multiple cross-bridges with actin

-Myosin heads “slide” thin filaments toward the center of the A band
   -Note: filaments do not change length!

-Effect: when the filaments “slide,” the sarcomere shortens and generates tension in the muscle
-This is why muscle fibers shorten when they contract!

50
Q

Motor Units

A

-A single motor neuron can serve multiple muscle fibers
-BUT: A single muscle fiber is served by only ONE motor neuron

-Motor unit: a single motor neuron and all the muscle fibers it innervates

51
Q

What is the result of stimulation by 1 motor neuron?

A

cause a widespread weak contraction; if all stimulated at the same time, it would be a much stronger contraction in one part of the muscle

52
Q

Motor Unit rule 1

A

-when the motor neuron fires: all fibers it innervates will contract
-Fibers innervated by a single motor neuron are spread out over entire muscle: not clumped together!

53
Q

Motor Unit rule 2

A

-number of muscle fibers a single motor neuron innervates influences movement
-Motor neuron innervating few fibers
VS.
-Motor neuron innervating many fibers

54
Q

What is the result on movement for each innervating fiber type?

A

-few fibers = very precise, fine-tuned control
-many fibers = not as precise

55
Q

Muscle Twitch

A

-Definition: response of a muscle to a single stimulus

-Measured with a twitch myogram

56
Q

3 phases of a myogram

A

1) Latent period: first few milliseconds following stimulation
-Excitation-contraction coupling occurs, but no tension observable in muscle

2) Period of contraction
-Active cross-bridge formation with increasing tension

3) Period of relaxation
-Cross bridge formation declines, muscle tension declines to resting value

57
Q

Graded Muscle Contractions

A

-Definition: sustained muscle contraction that is modified by the nervous system to produce varying amounts of force

-Muscle contractions can be graded 2 ways:
1) Temporal summation: increasing the frequency of stimulation of a muscle

2) Motor Unit summation: increasing the strength of stimulation of a muscle

58
Q

Temporal Summation

A

-Increasing the firing rate of a motor neuron can generate more force at the muscle

-How does it happen?
-Fire stimuli in rapid successionthe second twitch hits the muscle before the first twitch has ended
-Effect: muscle tension increases

59
Q

Temporal summation can lead to 2 forms of tetanus

A

1) Unfused (incomplete) tetanus: rate of stimulation creates a sustained & quivering muscle contraction
-ex. when you lift something heavy and your muscles shake
-some relaxation occurs

2) Fused (complete) tetanus: rate of stimulation creates smooth, sustained muscle contraction
-No relaxation occurs
-most force you can possibly produce by the muscle
-can be damaging overtime because the muscle fibers use large amounts of ATP at once

60
Q

Motor unit summation

A

-Definition: recruitment of additional motor units in a muscle to generate more force during contraction

-How does it happen?
-Increase the number of motor units used over time during contraction

-Size principal of motor unit summation
     -Motor units with smallest muscle fibers recruited first

   -Motor units with largest muscle fibers recruited last: create most force

-Motor units recruited asynchronously: some contracting, others relaxing

61
Q

Why are motor units recruited asynchronously?

A

-if you use every muscle fiber at the same time, you will fatigue that muscle really quickly and not be able to use it
-trade-off which ones are resting and working
-allows you to vary the force exerted and duration of exertion

62
Q

Muscle Tone

A

-Relaxed muscles are always slightly contracted: creates muscle tone

-Does not produce movement
-So why is it important?
-Muscle tone keeps muscle tissue healthy and responsive, stabilizes joints, maintains posture (ex. holding your neck up)
-allows muscles to remain excitable

     -Loss of muscle tone leads to loss of responsiveness
           -Muscle will not respond to stimuli
           -Ex: stroke victims
63
Q

Types of Muscle Contraction

A

-Isotonic contraction
-Isometric Contraction

64
Q

Isotonic contraction

A

-muscle tension develops to overcome the load, muscle shortening occurs
-Two subtypes:
1) Concentric contraction: muscle shortens and does work
-Ex: upward motion of a bicep curl

     2) Eccentric contraction: muscle generates force as it lengthens
         -Ex: downward motion of a bicep curl
         -50% stronger than the concentric contraction
65
Q

Isometric Contraction

A

-tension develops in a muscle, but the length of the muscle does not change
-Occurs when the load is not moved

-Cross-bridge formation still occurs, but: the actin filaments do not slide

-Ex: most muscles responsible for body posture, plank position, wall sits, etc.

66
Q

Energy Needs for Contraction

A

-ATP is the only energy source used directly for contractile activity
-Skeletal muscle stores energy in the form of glycogen

-ATP regenerated as fast as it is used

-3 Pathways used to regenerate ATP:
      1) Direct phosphorylation
      2) Anaerobic pathways
      3) Aerobic pathways
67
Q

Direct Phosphorylation

A

-Creates ATP from ADP + Pi using creatine phosphate (CP)
-Catalyzed by creatine kinase

-1 ATP produced per CP molecule

-Does not require oxygen

-Supplies ~15 s worth of ATP

68
Q

Anaerobic Pathways: Glycolysis & Lactic Acid Formation

A

-Glucose broken down to form 2 ATP & pyruvic acid
-In absence of O2pyruvic acid converted to lactic acid
-Lactic acid not used by musclediffuses into blood

-Does not require oxygen

-Fast method to create ATP

-Drawbacks:
-A lot of glucose used for low ATP yield (2 ATP)
-Lactic acid build-up results in DOMS (delayed onset muscle soreness)

-Stored glycogen, creatine phosphate, & glycolysis provide ~1 minute of ATP

69
Q

Aerobic Pathway: Cellular Respiration

A

-Creates 95% of ATP used by muscle during rest and light to moderate long-term exercise
-Requires pyruvic acid produced in anaerobic pathway

-Requires oxygen and mitochondria

-Produces ~30 ATP, H20, and CO2

-Drawbacks:
-Slow process
-Requires constant O2 and glucose

70
Q

Muscle Fatigue

A

-We can produce ATP: but it is not unlimited
-Muscle fatigue occurs: muscle is physiologically incapable of contracting

-Rate & duration of fatigue depends on activity
-High intensity exercise (ex. HIT workouts) VS.
-Low intensity exercise (ex. marathon running)

71
Q

Why is muscle fatigue necessary and important? What happens to muscle fibers if ATP is completely depleted?

A

-muscle fatigue prevents a muscle cell from running out of ATP because if it runs out of ATP, it dies
-your skeletal muscle cells have other activities to keep them alive that require ATP

72
Q

How quickly will high-intensity vs low-intensity exercise cause fatigue? What is the duration of fatigue for each?

A

-High-intensity exercise = muscle tires out quickly, rate of fatigue is fast, but the duration of fatigue is short
-Low-intensity exercise = muscle tires out at a slower rate, rate of fatigue is slow, but the duration of fatigue is long

73
Q

Muscle Contraction: Force

A

-Force of contraction is determined by the number of cross-bridges formed between myosin and actin filaments
-More cross bridges = more force

74
Q

Force of muscle contraction is influenced by 4 factors

A

1) Frequency of stimulation: temporal summation

2) Number of muscle fibers recruited: motor unit summation

3) Size of muscle fiber
-Bulkier muscle generates more tension, creates more force

-Hypertrophy: increase size of muscle fibers in muscle to increase force generated

-Rate of hypertrophy dependent on genetics, sex, nutrition, etc.

4) Degree of muscle stretch
-Force a muscle creates varies with how much the muscle is stretched
-Length-tension relationship: the maximal force produced will differ based on the degree of muscle stretch or contraction (optimal overlap is going to generate the most force)

75
Q

Why can bulkier muscles generate more tension and force?

A

larger muscle fibers have more myofibrils, more myofibrils have more myofilaments, and more myofilaments mean more cross-bridges that can be formed

76
Q

Why can muscle generate less tension when the sarcomeres are stretched? Shortened?

A

-when the sarcomeres are shortened, there is so much overlap between myofilaments that they cannot move anywhere and cannot form cross-bridges
-when the sarcomeres are stretched, there is no overlap between myofilaments, the myosin heads have nothing to physically attach themselves to and cannot form cross-bridges
-cannot generate a lot of force in either of these situations

77
Q

Muscle Contraction: Velocity & Duration

A

-Fiber type influences velocity & duration of muscle contraction
1) Speed of contraction
-Dependent on:
A) How fast ATP is split: how fast cross bridges can form & break
B) Electrical activity of motor neurons: fast neurons = fast contraction

2) Load and recruitment Small loads allow faster contraction More motor unit recruitment = faster contraction

3) Pathway of ATP production Oxidative fibers: use aerobic pathways Glycolytic fibers: use anaerobic pathways

-Three fiber types created from different combinations of the above: fast glycolytic, fast oxidative, & slow oxidative

78
Q

Slow Oxidation Fibers

A

-speed of contraction & ATP breakdown = slow
-myoglobin content = high
-glycogen content = low
-fatigue = slow
-mitochondria = many
-capillary supply = many
-example activities = anything endurance

79
Q

Fast Oxidative Fibers

A

-speed of contraction & ATP breakdown = fast
-myoglobin content = high
-glycogen content = intermediate
-fatigue = intermediate
-mitochondria = many
-capillary supply = many
-example activities = sprinting, walking

80
Q

Fast Glycolytic Fibers

A

-speed of contraction & ATP breakdown = fast
-myoglobin content = low (doesn’t use oxygen)
-glycogen content = high
-fatigue = fast
-mitochondria = few
-capillary supply = few
-example activities = intense, powerful movement

81
Q

Gross Anatomy of Smooth Muscle Tissue

A

-Hollow organs in the body have smooth muscle tissue

-Most organs have 2 layers of smooth muscle tissue that never contract simultaneously in the same area:
1) Longitudinal layer: muscle fibers run the
length of the organ
-More superficial

2) Circular layer: muscle fibers run the circumference of the organ
-Deep to longitudinal layer

82
Q

What organ does not have smooth muscle tissue?

A

heart has cardiac muscle tissue

83
Q

What happens to the organ when the longitudinal layer contracts?

A

leads to the organ becoming shorter and wider

84
Q

What happens to the organ when the circular layer contracts?

A

organ becomes long and thin

85
Q

Differences between smooth muscle fibers and skeletal muscle fibers

A

1) Smooth muscle fibers are short, spindle-shaped

2) Covered only by endomysium

3) No neuromuscular junctions

4) Smooth muscle fibers have no T-tubules & less sarcoplasmic reticulum

5) Muscle fibers have gap junctions

6) No striations or sarcomeres

7) No troponin

8) Thick and thin filaments arranged diagonally

86
Q

No neuromuscular junctions (smooth muscle tissue)

A

-innervation forms varicosities
-Autonomic fibers have bulb-like swellings scattered over smooth muscle tissue surface

 -Importance: creates diffuse junctions
      -Wide synaptic clefts that release neurotransmitter to multiple muscle fibers
87
Q

Smooth muscle fibers have no T-tubules & less sarcoplasmic reticulum (smooth muscle tissue)

A

-Sarcoplasmic reticulum releases only a small amount of Ca2+

-Caveolae: invaginations of of sarcolemma of muscle fiber
-Have Ca2+ ion channels

88
Q

Where does the calcium come from in caveolae?

A

extracellular fluid (outside of the cell)

89
Q

Muscle fibers have gap junctions (smooth muscle tissue)

A

Depolarization spreads from cell to cell

90
Q

No striations or sarcomeres (smooth muscle tissue)

A

-There are still thick and thin filaments, but:
-Fewer thick filaments overall
-Myosin heads found along entire length of thick filament

91
Q

No troponin (smooth muscle tissue)

A

Calmodulin: protein that acts as Ca2+ binding site

92
Q

Thick and thin filaments arranged diagonally (smooth muscle tissue)

A

-Filaments spiral down axis of muscle fiber
-Effect: when a muscle fiber contracts: it twists

93
Q

Types of Smooth Muscle

A

-Unitary smooth muscle
-Multi-unit smooth muscle

94
Q

Unitary smooth muscle

A

-Everything described so far are characteristics of unitary smooth muscle

-Much more commonfound in hollow organs

95
Q

Multi-Unit smooth muscle

A

-Have no gap junctions or spontaneous depolarization
-Muscle fibers are structurally independent
-Forms motor units
-Have graded contractions with recruitment

-Found in arrector pili, smooth muscle of airways, internal eye muscles

96
Q

Regulation of Contraction

A

-Neural Regulation
-Hormones & Local Chemical Factors

97
Q

Neural Regulation

A

-Neurotransmitter can excite or inhibit smooth muscle tissue

-Response is dependent on receptor molecules on sarcolemma

98
Q

Hormones & Local Chemical Factors

A

-Some smooth muscle has no innervation: respond only to local chemicals
-Others spontaneously depolarize

-Act by enhancing or inhibiting Ca2+ entry into sarcoplasm

99
Q

Unique Features of Smooth Muscle

A

1) Response to stretch
2) Length and tension changes

100
Q

Response to stretch (smooth muscle tissue)

A

-Smooth muscle responds to stretch by contracting
-Importance: increases ability to push substances through organ

 -Stress-relaxation response: if an organ is filled slowly, it will not contract strongly
101
Q

Length and tension changes (smooth muscle tissue)

A

-Smooth muscle can stretch more & can generate more tension while stretched
-Can still contract when stretched 150% its length

Anatomy & Physiology (15 decks)

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