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Human Physiology > Muscle Physiology > Flashcards

Muscle Physiology Flashcards

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
Q

Sarcomeres: Thick Filaments

A
  • 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
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26
Q

Communication of Nervous System with Skeletal Muscles

A
  • 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
Q

Steps that initiate a Muscle Contraction: Summary

A

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
Q

Steps that initiate a Muscle Contraction: ACh released

A

ACh is released at the neuromuscular junction and binds to ACh receptors on the sarcolemma

29
Q

Steps that initiate a Muscle Contraction: Action potential reaches T tubule

A

An action potential is generated and spreads across the membrane surface of the muscle fibre and along the T tubule

30
Q

Steps that initiate a Muscle Contraction: Sarcoplasmic reticulum releases Ca2+

A

The sarcoplasmic reticulum releases stored calcium ions

31
Q

Steps that initiate a Muscle Contraction: Active site exposure and cross bridge formation

A

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
Q

Steps that initiate a Muscle Contraction: Contraction cycle begins

A

The contraction cycle beings as repeated cycles of cross-bridge binding, pivoting, and detachment occur - All powered by ATP

33
Q

The contraction cycle: Summary

A

1) Contraction Cycle Begins
2) Active-site exposure
3) Cross-bridge formation
4) Myosin Head pivoting
5) Cross-bridge detachment
6) Myosin reactivation

34
Q

The contraction cycle: Contraction Cycle Begins

A

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
Q

The contraction cycle: Active-site exposure

A

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
Q

The contraction cycle: Cross-bridge formation

A

Once the active sites are exposed, the energised myosin heads bind to them, forming cross-bridges

37
Q

The contraction cycle: Myosin Head pivoting

A

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
Q

The contraction cycle: Cross-bridge detachment

A

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
Q

The contraction cycle: Myosin Reactivation

A

Myosin reactivation occurs when the free myosin head splits ATP into ADP + P. The energy released is used to recock the myosin head

40
Q

Steps that End a muscle contraction: Summary

A

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
Q

Steps that End a muscle contraction: ACh is broken down

A

ACh is broken down by AChE, ending action potential generation

42
Q

Steps that End a muscle contraction: Sarcoplasmic reticulum reabsorbs Ca2+

A

As the calcium ions are reabsorbed, their concentration in cytosol decreases

43
Q

Steps that End a muscle contraction: Active sites covered, cross-bridge formation ends

A

Without calcium ions, the tropomyosin returns to its normal position and the active sites are covered again

44
Q

Steps that End a muscle contraction: Contraction Ends

A

Without cross-bridge formation, contraction ends

45
Q

Steps that End a muscle contraction: Muscle relaxation occurs

A

The muscle returns passively to its resting length

46
Q

Muscle Tissue: Skeletal

A
  • Multinucleated, striated, voluntary

e. g. face expressions attached to bones

47
Q

Muscle Tissue: Cardiac

A
  • Mononucleated, striated, involuntary, intercalated discs

e. g. heart

48
Q

Muscle Tissue: Smooth

A
  • Mononucleated, non-striated, involuntary

e. g. blood vessels

49
Q

Sarcomere shortening and Muscle Fibre Stimulation

A
  • 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
Q

Twitch

A

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
Q

Single Twitch

A
  • Single action potential

- Contraction then relaxation

52
Q

Multiple Contractions

A
  • Treppe - cardiac muscle
  • Wave summation
  • Tetanus
53
Q

Skeletal muscle contraction: Isotonic contraction

A

Muscle length shortens to move load

54
Q

Skeletal muscle contraction: Isometric contraction

A

Tension in muscle, no change in muscle length

55
Q

ATP and muscle contraction

A
  • 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
Q

ATP and muscle contraction: Oxygen Debt or Excess post exercise oxygen consumption

A
  • Created during exercise

- Amount of oxygen required during recovery period to restore muscle to normal condition

57
Q

Muscle Fibre Type: Fast fibres

A

Large in diameter, contain densely packed myofibrils, few mitochondria. Produce rapid and powerful contractions of relatively brief duration

58
Q

Muscle Fibre Type: Slow fibres

A

Half-diameter of fast fibres, take three times long to contract after stimulation

59
Q

Muscle Fibre Type: Intermediate Fibres

A

Similar to fast fibres but have a greater resistance to fatigue

60
Q

Muscle Fibre Type: White muscles

A

Muscles dominated by fast fibres, appear pale

61
Q

Muscle Fibre Type: Red muscles

A

Muscles dominated by slow fibres risk in myoglobin, red

62
Q

Anaerobic Endurance

A

Time over which muscular contractions can be sustained by glycolysis and reserves of ATP and CP

63
Q

Aerobic Endurance

A

Time over which a muscle can continue to contract while supported by mitochondrial activities

Human Physiology (8 decks)

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