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Human Physiology > Muscle Physiology > Flashcards

Muscle Physiology Flashcards

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1
Q

Functions of the muscle system

A
  • Produce skeletal movement
  • Maintain posture and body position
  • Support soft tissues
  • Guard entrances and exits
  • Maintain body temperature
  • Store nutrient reserves
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2
Q

Functions of the muscle system: Produce skeletal movement

A

Skeletal muscle contractions pull on tendons and move the bones of the skeleton

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3
Q

Functions of the muscle system: Maintain posture and body position

A

Tension in skeletal muscles maintains body posture

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4
Q

Functions of the muscle system: Support soft tissues

A

Support weight of our visceral organs and shield our internal tissues from injury

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5
Q

Functions of the muscle system: Guard entrances and exits

A

Gives us voluntary control over swallowing, defecation and urination

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6
Q

Functions of the muscle system: Maintain body temperature

A

Heat released by working muscles keeps body temperature in the range needed for normal functioning

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7
Q

Structure of Muscle Tissue

A 
Organisation of connective tissues
- Epimysium
- Perimysium
- Endomysium
Skeletal muscle (organ)
Muscle Fascicle/Bindle (bundle of fibres)
Muscle fibre (cell)
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8
Q

Structure of Muscle Tissue: Epimysium

A

Dense layer of collagen fibres that surrounds entire muscle. Separates muscle from nearby tissues and organs

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9
Q

Structure of Muscle Tissue: Perimysium

A

Divides the skeletal muscle into a series of compartments. Contains blood vessels and nerves

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10
Q

Structure of Muscle Tissue: Endomysium

A

Surrounds individual skeletal muscle cells, called muscle fibres and loosely interconnects adjacent muscle fibres. Contains blood vessels

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11
Q

Skeletal Muscle Fibres (Distinctive Features)

A
  • Diameter from 100micrometres to 30cm

- Multinucleate

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12
Q

Skeletal Muscle Fibres: Sarcolemma

A
  • Surrounds sarcoplasm
  • Has characteristic transmembrane potential due to the unequal distribution of positive and negative charges across the membrane (sudden change in transmembrane potential can lead to a contraction)
  • All regions of cell must contract at the same time and therefore, signal must be distributed quickly
  • Signal is conducted through transverse tubules
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13
Q

Skeletal Muscle Fibres: Transverse Tubules

A
  • Narrow tubes that are continuous with the sarcolemma and extend deep into the sarcoplasm
  • Filled with extracellular fluid and form passageways through the muscle fibre
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14
Q

Skeletal Muscle Fibres: Myofibrils

A
  • Can actively shorten and are responsible for skeletal muscle fibre contraction
  • 1-2 micrometre in diameter and as long as the entire cell
  • Consist of myofilaments
    > thin filaments: actin
    > thick filaments: myosin
    - titin
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15
Q

Skeletal Muscle Fibres: Sarcoplasmic reticulum

A
  • forms tubular network around each individual myofibril
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16
Q

Skeletal Muscle Fibres: Sarcomeres

A
  • Myofilaments are organised into repeating functional units called sarcomeres
  • Smallest, functional units of muscle fibres
  • Myofibril consists of about 10000 sarcomeres, each with a resting length of about 2micrometres.
  • Contains thick filaments, think filaments, a protein to stabilise the positions of filaments and proteins that regulate the interactions between thick and thin filaments
  • A band
  • I Band
  • Thin filaments
  • Thick filaments
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17
Q

Sarcomeres: A Band

A
  • Dark bands

- As long as typical thick filament and includes portions of thin filaments, contains 3 subdivisions

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18
Q

Sarcomeres: A Band: M line

A

Proteins of the M line connect the central portion of each thick filament. Help stabilise the positions of the thick filaments

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19
Q

Sarcomeres: A Band: H Band

A

In resting sarcomere, H band is a lighter region on either side of the M line. Only contains thick filaments

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20
Q

Sarcomeres: A Band: Zone of overlap

A

Dark region where thin filaments are located between thick filaments

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21
Q

Sarcomeres: I Band

A

Only contains thin filaments and extends from the A band of one sarcomere to the A band of the next sarcomere

  • Z lines
  • Titin
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22
Q

Sarcomeres: I Band: Z Lines

A

Mark boundary between adjacent sarcomeres, consist of proteins called actinins

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23
Q

Sarcomeres: I Band: Titin

A

Extend from tips of the thick filaments to attachment sites at the Z line

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24
Q

Sarcomeres: Thin Filaments

A
  • Four proteins: F-actin, nebulin, tropomyosin and troponin
  • Tropomyosin cover active sites on G-actin subunits that form the F-actin strand
  • Troponin binds to G-actin and tropomyosin and holds the tropomyosin in position
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25
Sarcomeres: Thick Filaments
- Consist of a bundle of myosin molecules around a titin core - Each myosin molecule: long tail and globular head which forms cross-bridges with a thin filament during contraction
26
Communication of Nervous System with Skeletal Muscles
- Communication between the nervous system and a skeletal muscle fibre occurs at a neuromuscular junction (NMJ) - Neuron stimulates a muscle fibre through a series of steps
27
Steps that initiate a Muscle Contraction: Summary
1) ACh released 2) Action potential reaches T tubule 3) Sarcoplasmic reticulum releases Ca2+ 4) Active site exposure and cross bridge formation 5) Contraction cycle begins
28
Steps that initiate a Muscle Contraction: ACh released
ACh is released at the neuromuscular junction and binds to ACh receptors on the sarcolemma
29
Steps that initiate a Muscle Contraction: Action potential reaches T tubule
An action potential is generated and spreads across the membrane surface of the muscle fibre and along the T tubule
30
Steps that initiate a Muscle Contraction: Sarcoplasmic reticulum releases Ca2+
The sarcoplasmic reticulum releases stored calcium ions
31
Steps that initiate a Muscle Contraction: Active site exposure and cross bridge formation
Calcium ions bind to troponin, exposing the active sites on the thin filaments. Cross-bridges form when myosin heads bind to those active sites
32
Steps that initiate a Muscle Contraction: Contraction cycle begins
The contraction cycle beings as repeated cycles of cross-bridge binding, pivoting, and detachment occur - All powered by ATP
33
The contraction cycle: Summary
1) Contraction Cycle Begins 2) Active-site exposure 3) Cross-bridge formation 4) Myosin Head pivoting 5) Cross-bridge detachment 6) Myosin reactivation
34
The contraction cycle: Contraction Cycle Begins
The contraction cycle involves a series of interrelated steps. It begins with the arrival of calcium ions within the zone of overlap in a sarcomere
35
The contraction cycle: Active-site exposure
Calcium ions bind to troponin, weakening the bond between actin and the troponin-tropomyosin complex. The troponin molecule then changes position, rolling the tropomyosin molecule away from the active sites on actin and allowing interaction with the energised myosin heads
36
The contraction cycle: Cross-bridge formation
Once the active sites are exposed, the energised myosin heads bind to them, forming cross-bridges
37
The contraction cycle: Myosin Head pivoting
After cross-bridge formation, the energy that was stored in the resting state is released as the myosin head pivots toward the M line. This action is called the power stroke when it occurs, the bound ADP and phosphate group are released
38
The contraction cycle: Cross-bridge detachment
When another ATP binds to the myosin head, the link between the myosin head and the active site on the actin molecule is broken. The active site is now exposed and able to form another cross-bridge
39
The contraction cycle: Myosin Reactivation
Myosin reactivation occurs when the free myosin head splits ATP into ADP + P. The energy released is used to recock the myosin head
40
Steps that End a muscle contraction: Summary
6) ACh is broken down 7) Sarcoplasmic reticulum reabsorbs Ca2+ 8) Active sites covered, cross-bridge formation ends 9) Contraction ends 10) Muscle relaxation occurs
41
Steps that End a muscle contraction: ACh is broken down
ACh is broken down by AChE, ending action potential generation
42
Steps that End a muscle contraction: Sarcoplasmic reticulum reabsorbs Ca2+
As the calcium ions are reabsorbed, their concentration in cytosol decreases
43
Steps that End a muscle contraction: Active sites covered, cross-bridge formation ends
Without calcium ions, the tropomyosin returns to its normal position and the active sites are covered again
44
Steps that End a muscle contraction: Contraction Ends
Without cross-bridge formation, contraction ends
45
Steps that End a muscle contraction: Muscle relaxation occurs
The muscle returns passively to its resting length
46
Muscle Tissue: Skeletal
- Multinucleated, striated, voluntary | e. g. face expressions attached to bones
47
Muscle Tissue: Cardiac
- Mononucleated, striated, involuntary, intercalated discs | e. g. heart
48
Muscle Tissue: Smooth
- Mononucleated, non-striated, involuntary | e. g. blood vessels
49
Sarcomere shortening and Muscle Fibre Stimulation
- Sarcomere shortening and muscle fibre stimulation produce tension - Amount of tension produced by a muscle fibre depends on the number of cross-bridges formed - Skeletal muscle fibres can contract most forcefully when stimulated over a narrow range of resting lengths
50
Twitch
A twitch is a cycle of contraction and relaxation produced by a single stimulus Slow twitch: less powerful but fatigue slowly-fewer myofibrils, more mitochondria Fast Twitch: more powerful but fatigue fast - lots of myofibrils
51
Single Twitch
- Single action potential | - Contraction then relaxation
52
Multiple Contractions
- Treppe - cardiac muscle - Wave summation - Tetanus
53
Skeletal muscle contraction: Isotonic contraction
Muscle length shortens to move load
54
Skeletal muscle contraction: Isometric contraction
Tension in muscle, no change in muscle length
55
ATP and muscle contraction
- Aerobic metabolism can provide most of the ATP needed to support muscle contractions - Muscle cell relies on glycolysis to generate ATP at peak - Fatigued muscle can no longer contract because of a drop in pH due to the buildup and dissociation of lactic acid - Recovery period begins after a period of muscle activity and continues until conditions inside the muscle have returned to pre-exertion levels
56
ATP and muscle contraction: Oxygen Debt or Excess post exercise oxygen consumption
- Created during exercise | - Amount of oxygen required during recovery period to restore muscle to normal condition
57
Muscle Fibre Type: Fast fibres
Large in diameter, contain densely packed myofibrils, few mitochondria. Produce rapid and powerful contractions of relatively brief duration
58
Muscle Fibre Type: Slow fibres
Half-diameter of fast fibres, take three times long to contract after stimulation
59
Muscle Fibre Type: Intermediate Fibres
Similar to fast fibres but have a greater resistance to fatigue
60
Muscle Fibre Type: White muscles
Muscles dominated by fast fibres, appear pale
61
Muscle Fibre Type: Red muscles
Muscles dominated by slow fibres risk in myoglobin, red
62
Anaerobic Endurance
Time over which muscular contractions can be sustained by glycolysis and reserves of ATP and CP
63
Aerobic Endurance
Time over which a muscle can continue to contract while supported by mitochondrial activities

Human Physiology (8 decks)

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