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MBBS II MSS > L12 - Physiology and regulation of skeletal muscle  contraction > Flashcards

L12 - Physiology and regulation of skeletal muscle  contraction Flashcards

1
Q

Compare between skeletal, cardiac and smooth muscle: Myofibril structure.

A

Skeletal: Striated
Cardiac: Striated
Smooth:Non-striated (lack of sacromere)

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2
Q

Compare between skeletal, cardiac and smooth muscle: Shape

A

Skeletal: Long, cylindrical
Cardiac: Small, branched
Smooth: Spindle- shape

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3
Q

Compare between skeletal, cardiac and smooth muscle: Nucleus

A

Skeletal: Multi-nucleated, peripheral
Cardiac: Single, central
Smooth: Single, central

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4
Q

Compare between skeletal, cardiac and smooth muscle: T- tubules

A

Skeletal: Long
Cardiac: Short
Smooth: None

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5
Q

Describe the structure of thin filament myofibrils?

A

Attaches at Z line

F-actin strand with G-actin molecules / subunits (active site)

Troponin-tropomyosin complexes lie parallel to F-actin strands: tropomyosin covers active site on G actin

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6
Q

Describe the structure of thick filament myofibrils?

A
  • Myosin (with head, tail and hinge)

- Titin which spansthedistancefromoneZdisktotheneighboringMline

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7
Q

What are the giant accessory proteins in myofilments?

A

Titin and Nebulin

Titin = provide elasticity and stabilize myosin

Nebulin = align actin

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8
Q

List the changes to a sacromere during contraction.

A

sarcomeres shorten simultaneously during contraction

A band stays the same width

I band gets smaller, H bands narrows

Z lines move closer together

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9
Q

How does zero Zone of overlap between myofilaments dictate the amount of force produced?

A

Too little overlap = contraction cannot occur

  • thinandthickfilaments cannotinteractatall
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10
Q

What is the tension generated when the zone of overlap between myofilaments increases beyond the optimal point?

A

1) At short resting lengths, thin filaments extend across the centre of sacromere (M line)
» Interfere with normal orientation of myofilaments
» reduce tension production

2) When thick filaments contact the Z line, the sacromere cannot shorten
» Myosin heads cannot pivot
» No tension produced

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11
Q

Under what zone of overlap between myofilaments is maximum force generated?

A

zone of overlap is large but thin filaments do not extend across sarcomere’s center

> > all myosin heads can bind to actin

> > produce maximum tension

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12
Q

What prevents overstretching of sacromeres?

A

Extreme stretching of muscle fiber is normally prevented by:

Titin filaments (tie thick filaments to Z lines)

Surrounding connective tissues

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13
Q

Describe the role of Ca2+ in excitation-contraction coupling. Start with the NMJ.

A

1) Somatic motor neuron releases Ach, activate AchR and influx of Na+, initiate muscle AP
2) Action potential propagates down T-tubules
3) Change conformation of dihydropyridine (DHP) receptor (= voltage-gated L-type calcium channel
4) DHP receptor opens ryanodine (RyR) receptor (= calcium-releasing channel) in sarcoplasmic reticulum&raquo_space; Ca2+ enters cytoplasm
5) Ca2+ binds to troponin&raquo_space; allows actin-myosin binding (cross-bridge formation)&raquo_space; Myosin head power stroke …etc

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14
Q

List the events that occur during cross-bridge cycles. Start with Ca2+ entering cytoplasm of sacromere

A

At rest, tropomyosin covers active binding sites on G-actin

1) Ca2+ increase in cytosol, binds to troponin
2) Troponin-Ca2+ complex rotates, pulls tropomyosin away to expose actin’s myosin-binding site
3) Myosin binds to actin (form cross-bridge)&raquo_space; completes power stroke
5) Actin filament moves

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15
Q

Explain the role of ATP in the cross-bridge cycles in sacromeres?

A

1) Binding of ATP onto myosin head detaches cross-bridge
2) Hydrolysis of ATP into ADP + Pi causes myosin reactivation&raquo_space; recock into higher energy position
3) Removal of inorganic phosphate (Pi)&raquo_space; cross-bridge strengthening
4) Removal of ADP&raquo_space; Power stroke

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16
Q

What is catabolized for ATP in resting muscle? What is this ATP used for?

A

Fatty acid from aerobic respiration in mitochondria

Used for building energy reserves of ATP in Creatine phosphate or Glycogen

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17
Q

What is catabolized for ATP in moderate activity muscle? What is this ATP used for?

A

Glucose (from glycogen) and fatty acids (from mitochondria) are catabolized

Needs adequate supply of oxygen.

Used for power contraction

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18
Q

What is catabolized for ATP in peak activity muscle? What is this ATP used for?

A

Mostly glucose from glycogen
Also from Creatine phosphate and aerobic mitochondrial activity

Produces lactate as by-product (muscle fatigue)

19
Q

Which energy source can sustain the longest Duration of isometric tetanic contraction?

A

Glycogen through Glycolysis (anaerobic) and Aerobic metabolism

20
Q

What causes Delayed Onset Muscle Soreness?

A

Eccentric contraction produces more soreness than concentric or isometric contraction

> > Small tears in sacrolemma permit enzymes and chemicals to stimulate nearby nociceptors

> > Tears in connective tiisue and tendon of skeletal muscle

21
Q

Explain the latent period between muscle AP stimulus and the development of maximum tension?

A

Time needed for:

Conduction of action potential; and

Subsequent release of Ca2+ by sarcoplasmic reticulum

22
Q

What is the difference between isotonic and isometric contraction?

A

Isotonic = Same tension

Isometric = Same length of muscle

23
Q

What are the different types of contraction resulting from increasing frequency of stimuli?

A

Single twitch

Summation

Summation leading to Unfused tetanus

Summation leading to complete tetanus

24
Q

What are the two types of isotonic contractions?

A

Concentric and Eccentric

25
Q

Difference between concentric and eccentric contraction?

A

In both cases the muscle length changes

Concentric = Muscle is attached to a weight < its peak tension capabilities, able to shorten during contraction to lift weight

Eccentric = Muscle attached to weight > its peak tension capabilities, UNABLE to shorten during contraction, weight elongates muscle until:

  • Muscle or tendon breaks, or;
  • Elastic recoil of muscle is enough to suspend the weight
26
Q

What occurs during Isometric contraction?

A

Muscle loaded by weight beyond its capacity

Muscle contracts but does not shorten, Muscle length unchanged

27
Q

What is the difference between muscle performance and muscle endurance?

A

Muscleperformance–themaximumamountoftension (force)producedbyaparticularmusclegroup.

Endurance–theamountoftimeduringwhichthe individualcanperformaparticularactivity

28
Q

How does blood test indicate damage to muscles?

A

Levels of creatine kinase, myoglobin = elevated in blood

29
Q

List the differences between slow and fast fibers?

A

Difference in:

  • Diameter
  • Time to peak twitch tension
  • Contraction speed
  • Myoglobin content
  • Color
  • Fatigue
  • Capillary supply
30
Q

Compare between fast and slow fibers: Diameter.

A

Fast fibers: Large

Slow fibers: Small

31
Q

Compare between fast and slow fibers: Time to peak twitch tension and contraction speed.

A

Fast fibers: Rapid

Slow fibers: Slow

32
Q

Compare between fast and slow fibers: Myoglobin content

A

Fast fibers: Low myoglobin content

Slow fibers: High ‘’

33
Q

Compare between fast and slow fibers: Color

A

Fast fibers: White/ paler due to fewer myoglobin

Slow fibers: Red/ Darker due to myoglobin

34
Q

Compare between fast and slow fibers: Fatigue.

A

Fast fibers: Easy to fatigue

Slow fibers: Resistant

35
Q

Compare between fast and slow fibers: Capillary supply

A

Fast: Scarce

Slow: Dense (more extensive network)

36
Q

What are the Type I, II-A and II-B muscle fibers?

A 
I = Slow 
II-A = intermediate
II-B = Fast
37
Q

Athletictrainingcanincreasetheratio of which muscle fibers?

A

increasetheratioofintermediatefiberstofastfibers

38
Q

Define muscle hypertrophy?

A

Enlargement of stimulated muscle

Occurs in muscles that have been repeatedly stimulated to produce near-maximal tension

39
Q

What are the intracellular changes to hypertrophied muscle?

A

Increasefusionofsatellitecells,increaseprotein synthesis,reduceproteolysis» increasefibersize

  • More mitochondria
  • Higher concentration of glycolytic enzymes
  • Larger glycogen reserves
40
Q

Define muscle atrophy?

A

Reductioninmusclesize,tone,andpower

because Skeletal muscles that are not regularly stimulated by a motor neuron lose muscle tone and mass

41
Q

Define musclecramp?

A

sudden, painful andinvoluntarycontraction of skeletalmuscles

42
Q

What are some possible causes of muscle cramp?

A

•Inadequatebloodsupply •Nervecompression •Mineraldepletion

43
Q

Prevention of muscle cramps?

A

•Electrolytesupplementandhydration •Stretchyourmuscles

MBBS II MSS (31 decks)

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