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(UTEP) Exercise Physiology > Skeletal Muscle > Flashcards

Skeletal Muscle Flashcards

1
Q

Types of Muscle

A
  • Smooth
  • Cardiac
  • Skeletal
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2
Q

Smooth Muscle

A
  • Involuntary

- In the walls of blood vessels and internal organs

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3
Q

Cardiac Muscle

A
  • Controls itself with help from nervous and endocrine systems
  • Only in the heart
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4
Q

Skeletal Muscle

A
  • Voluntary muscle

- Over 600 throughout the body

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5
Q

Skeletal Muscle Chemical Composition

A
  • Water = 75%
  • Protein = 20% ((myosin, actin, and tropomyosin most abundant)
  • Salts and other substances = 5%
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6
Q

Skeletal Muscle Organization (deep to superficial)

A
  • Myofilaments combine to form…
  • Myofibrils combine to form…
  • Muscle Fibers AKA Muscle Cells combine to form…
  • Fasciculi combine to form…
  • Muscles
  • Myofilaments are surrounded by the sarcoplasmic reticulum
  • Myofibrils are surrounded by the sarcoplasm
  • Muscle fibers are bound by the sarcolemma
  • Muscle fibers are separated by endomysium
  • Fasciculus are bound by perimysium
  • Muscles are bound by epimysium
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7
Q

Sarcoplasm

A

Contains:

  • Nuclei
  • Mitochondria
  • Specialized organelles
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8
Q

Myofibril

A

Any of the elongated contractile threads found in striated muscle cells

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9
Q

Sarcolemma

A

Surrounds each muscle fiber and encloses the fiber’s cellular contents

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10
Q

Muscle Fiber

A
  • AKA muscle cell

- Bundle of myofibrils

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11
Q

Endomysium

A

Wraps each muscle fiber/cell and separates it from neighboring fibers

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12
Q

Fasciculus

A

A bundle of muscle fibers

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13
Q

Perimysium

A

Surrounds a bundle of fibers

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14
Q

Epimysium

A

Surrounds the entire muscle and then blends into the intramuscular tissue sheaths to form tendons

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15
Q

Sarcoplasmic Reticulum

A
  • Surrounds myofibrils

- Provides structural integrity to the cell

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16
Q

Blood Supply to Muscle

A
  • Enters and exits along the intramuscular connective tissue

- Adapts with training (how??)

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17
Q

Skeletal Muscle Ultrastructure

A
  • A single muscle fiber has myofibrils that lie parallel to the fiber’s long axis
  • Myofibrils contain smaller subunits called myofilaments
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18
Q

Myofilaments

A
  • ~85% consists of actin and myosin

- Other proteins either serve a structural function or affect protein filament interaction during muscle action

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19
Q

Other proteins present in myofilament

A
  • Tropomyosin
  • Troponin
  • Alpha-actinin
  • Beta-actinin
  • M protein
  • C protein
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20
Q

Sarcomere

A
  • Functional unit of the muscle fiber repeating between 2 z lines
  • Lie in series
  • Sarcomere length greatly determines the muscle’s functional properties
  • I band
  • A band
  • H zone
  • M band
  • Z line
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21
Q

I Band

A
  • Isotropic
  • Represents lighter area
  • Only actin is visible
  • Gets smaller with contraction
22
Q

A Band

A
  • Anisotropic
  • Represents darker area
  • Actin and myosin overlap
  • Remains the same size during contraction
  • H zone
  • M band
23
Q

H Zone

A
  • Center of A band

- Area of A band that only has myosin

24
Q

M Band

A
  • Bisects H zone

- Consists of protein structures that support arrangement of myosin filaments

25
Q

Z Line

A
  • Bisects I band

- Adheres to sarcolemma to provide structural stability

26
Q

Thin Filament

A
  • Actin
  • Troponin
  • Tropomyosin
27
Q

Thick Filament

A

Myosin

28
Q

Myosin Filaments

A

Bundles of molecules with polypeptide tails and globular heads

29
Q

Actin Filaments

A

2 twisted monomer chains bound by tropomyosin polypeptide chains

30
Q

Actin-Myosin Orientation

A
  • Thousands of myosin filaments lie along line of actin filaments in muscle fiber
  • 6 thin actin filaments encircle thicker myosin filament
  • In a single fiber, this arrangement consists of approximately 16 billion thick filaments and 64 billion thin filaments
31
Q

ATP Hydrolysis and Cross-Bridges

A
  • ATP hydrolysis activates myosin’s 2 heads, placing them in an optimal orientation to bind actin’s active sites
  • This pulls thin filaments and Z lines of sarcomere toward the middle
32
Q

Steps of Cross-Bridge Cycle

A
  1. Binding of myosin to actin (ADP + P)
    - Inorganic phosphate is released
  2. Power stroke (ADP)
    - Actin gets pulled toward the middle of the sarcomere
    - ADP is released
  3. Rigor (myosin is in low-energy form)
    - New ATP binds to myosin head
  4. Unbinding of myosin and actin
    - ATP is hydolyzed
  5. Cocking of the myosin head (myosin is in high-energy form) (ADP + P)
  6. Repeat
33
Q

Other Endosarcomeric Proteins

A
  • Titin
  • M-line proteins
  • Alpha-actinin
34
Q

Titin

A
  • Links end of thick filament to the Z-disc

- Keeps myosin in position

35
Q

M-line Proteins

A
  • Runs along the middle of the H-zone

- Important for spatial organization

36
Q

Alpha-Actinin

A

Strong attachment of actin molecules at the Z-disc

37
Q

Intracellular Tubule Systems

A
  • Lateral end of tubule channel within muscle fiber terminates in saclike vesicle that stores Ca2+
  • T-tubule system runs perpendicular to myofibril
  • T-tubule functions as a transportation network by spreading action potential from outer membrane
38
Q

Role of Calcium in Muscle Action

A
  • Ca2+ is released from vesicle and diffuses a short distance to “activate”actin filaments
  • Muscle action begins when myosin filament crossbridges attach to active sites on actin
  • Electrical excitation ceases, Ca2+ concentration in cytoplasm decreases, and the muscle relaxes
39
Q

Sequence of Muscle Action Events

A
  1. ACh is released from neuron into neuromuscular junction, diffuses across synaptic cleft, and attaches to ACh receptor on sarcolemma
  2. AP depolarizes transverse tubules
  3. T-tubule system depolarization causes Ca2+ release from sarcoplasmic reticulum lateral sacs
  4. Ca2+ binds to troponin-tropomyosin complex, releasing inhibition of myosin combining with actin
  5. Actin joins myosin ATPase to split ATP, provides energy release, which produces myosin crossbridge movement
  6. Muscle shortening occurs when new ATP binds to myosin, which breaks the actin-myosin bond and allows crossbridge dissociation from actin and sliding of thick and thin filaments
  7. Ca2+ removal restores troponin-tropomyosin inhibitory action. With ATP present, actin and myosin remain in the dissociated state.
  8. When muscle stimulation ceases, Ca2+ moves back into the sarcoplasmic reticulum lateral sacs through active transport
  9. Crossbridge activation continues when Ca2+ concentration remains high (from membrane depolarization) to inhibit troponin-tropomyosin action
40
Q

Muscle Fiber Type Differences

A

Fiber types differ in:

  • Primary mechanisms they use to produce ATP
  • Type of motor neuron innervation
  • Type of myosin heavy chain expressed
41
Q

4 Characteristics of Fast-Twitch Fibers (Type II)

A
  • High capability for transmission of APs
  • High myosin ATPase activity
  • Rapid Ca2+ release and reuptake (efficient sarcoplasmic reticulum)
  • High rate of crossbridge turnover
42
Q

Properties of Fast-Twitch Fibers

A
  • Rapid energy production for quick, powerful muscle action
  • 3-5x faster than slow-twitch ribers
  • Relies on well-developed, short-term glycolytic system for energy transfer
43
Q

Type II Fiber Subtypes

A
  • Type IIa
  • Type IIx (previously referred to as type IIb)
  • “New Type IIb
44
Q

Type IIa

A

Represents fast-oxidative-glycolytic fibers (FOG)

45
Q

Type IIx

A

Midway between a and b types in physiologic and metabolic characteristics

46
Q

“New” Type IIb

A
  • Possesses greatest anaerobic potential and most rapid shortening velocity
  • Represents “true” fast-glycolytic fiber
47
Q

4 Characteristics of Slow-Twitch Fibers

A
  • Low myosin ATPase activity
  • Slow calcium handling ability and shortening speed
  • Less well-developed glycolytic capacity
  • Large and numerous mitochondria
48
Q

Properties of Slow-Twitch Fibers

A
  • Generate energy for ATP resynthesis through aerobic system
  • Highly fatigue resistance
  • Slow shortening speed
49
Q

Contribution of fiber types during near-max exercise

A

Both slow- and fast- twitch contribute during near-max exercise

50
Q

All-or-Nothing Rule

A
  • For a motor unit to be recruited the potential must pass threshold, otherwise there’s no muscle action
  • If threshold is reached, all muscle fibers in the motor unit act maximally
  • More force is produced by activating more muscle units

(UTEP) Exercise Physiology (4 decks)

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