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+ CAPS 301: Muscle, Bodily Fluid, Cardio > Skeletal Muscle > Flashcards

Skeletal Muscle Flashcards

1
Q

Where are skeletal muscles located?

A

between bones

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2
Q

What are the functions of skeletal muscles? (3)

A
  • body movement (locomotion)
  • maintenance of posture
  • respiration (diaphragm and intercostal contractions)
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3
Q

Are skeletal muscle fibres striated or non-striated?

A

striated

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4
Q

Describe the organization of skeletal muscle fibres.

A
  • muscle contains fascicles (bundles) of muscle fibres

- muscle fibres contain myofibrils

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5
Q

What are the 3 investments of skeletal muscle?

A

epimysium
perimysium
endomysium

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6
Q

What is epimysium?

A

dense collagenous connective tissue that surrounds entire muscle

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7
Q

What is perimysium?

A

collagenous connective tissue that surrounds fascicles

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8
Q

What is endomysium?

A

fine sheath of connective tissue composed of reticular fibres that surround individual muscle fibres

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9
Q

Is skeletal muscle contraction voluntary or non-voluntary?

A

voluntary

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10
Q

What is the spontaneity of skeletal muscle contraction controlled by?

A

motor neurons – cell body of motor neuron is localized in ventral horn of spinal cord

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11
Q

What is the basal lamina?

A

external lamina – layer of extracellular matrix secreted by epithelial cells

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12
Q

Where is the basal lamina?

A

under endomysium, between plasma membrane of muscle fibre and endomysium

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13
Q

What does the basal lamina contain?

A

glycoproteins and collagen

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14
Q

How is the basal lamina continuous with the inside of the cell

A

basal lamina binds myofiber via dystroglycan-containing complex

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15
Q

What is the dystroglycan-containing complex?

A

multi-protein complex

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16
Q

What is the sarcolemma?

A

plasma membrane of muscle fibre

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17
Q

What is the myotendinous junction?

A

interface between muscle and tendon, where force is transmitted between the two tissues

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18
Q

What does the myotendinous junction do?

A

attaches muscles to bones

  • muscle fibres end at level of tendon
  • finger-like extensions at ends of muscle fibres insert into connective tissue of tendon
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19
Q

Describe the structure of myofibers.

  • shape
  • striated or non-striated
  • nuclei
A
  • lond, cylindrical
  • striated
  • multinucleated
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20
Q

Where are nuclei of myofibers?

A

at periphery, just under plasma membrane

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21
Q

What are myofibrils composed of?

A

myofilaments

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22
Q

How are myofibrils organized?

A
  • aligned in parallel

- separated by mitochondria and SR vesicles

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23
Q

What are myofibrils?

A

contractile muscle fibers

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24
Q

What is the sarcoplasmic reticulum?

A

smooth ER

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25
Q

Where is the sarcoplasmic reticulum and how is it organized?

A
  • runs longitudinally to myofibril

- surrounds individual myofibrils

26
Q

What does sarcoplasmic reticulum form? (2)

A
  • interconnected network of tubules

- chambers (lateral sacs) called terminal cisternae on either side of T-tubules

27
Q

What does the sarcoplasmic reticulum do in skeletal muscle?

A
  • major role in storing Ca2+ when muscle is at rest

- releases Ca2+ into sarcoplasm when muscle is stimulated

28
Q

What are transverse tubules (T-tubules)?

A

deep invaginations of sarcolemma, perpendicular to length of myofiber

29
Q

What is a triad junction?

A

single T-tubule + 2 terminal cisternae

30
Q

What receptors do T-tubules carry?

A

dihydropyridine receptors = voltage-gated Ca2+ channels

31
Q

What receptors do terminal cisternae carry?

A

ryanodine receptors = Ca2+ release channel

32
Q

What is the sarcomere?

A

contractile unit of myofibril made of 2 myofilaments

in skeletal and cardiac muscle

33
Q

What are the 2 types of myofilaments?

A
  • myosin (thick) myofilament

- actin (thin) myofilament

34
Q

What is the myosin myofilament made of?

A

myosin molecule, composed of 2 heavy chains of myosin

35
Q

What is the purpose of the myosin molecule head?

A

power stroke during contraction

36
Q

What are the two sites on the myosin molecule head?

A
  • actin binding site

- myosin ATPase site: where ATP binds and hydrolyzes into ADP and Pi

37
Q

What are actin myofilaments made of?

A
  • two actin filaments twisted to form helix

- proteins – tropomyosin, troponin complex

38
Q

What are actin filaments made of?

A

many g-actin (monomeric form of actin)

39
Q

What is a motor unit?

A

motor neuron and all muscle fibres it innervates

40
Q

What is the motor endplate?

A

specialized domain of sarcolemma

41
Q

What does the motor endplate do?

A

highly excitable, and is responsible for initiating AP that propagates across myofiber and causes contraction

42
Q

What is the neuromuscular junction (NMJ)?

A

junction between axon terminal of motor neuron and motor endplate

(synaptic contact between presynaptic terminal and postsynaptic membrane of muscle fiber)

43
Q

What are synpatic vesicles filled with?

A

ACh (neurotransmitter)

44
Q

What are junctional folds?

A

folds in postsynaptic membrane, particular to NMJ only (otherwise, membrane is usually flat)

45
Q

What is the synaptic cleft?

A

space between presynaptic membrane and postsynaptic membrane, where ACh in vesicles is released

46
Q

Does the NMJ have a basal lamina?

A

has a prominent basal lamina

47
Q

Does the NMJ have myelin?

A

no

48
Q

What is the nerve terminal filled with?

A

organelles – mitochondria, synaptic vesicles

49
Q

Where does endplate potential (EPP) occur?

A

in motor endplate, located underneath nerve terminal

50
Q

Can myosin head bind to actin at low Ca2+ concentration?

A

no

  • myosin binding sites on actin are masked by tropomyosin
  • blocks myosin head access to myosin binding site
51
Q

Can myosin head bind to actin at high Ca2+ concentration?

A

yes

  • myosin binding sites on actin are not masked by tropomyosin
  • myosin head can access myosin binding site and bind actin
52
Q

Where are there delays in contraction? Why?

A

between AP, Ca2+ release, and degeneration of force

Ca2+ needs to be released from SR, travel through sarcoplasm, find troponin complex, etc. – process takes time

53
Q

What is a single twitch?

A

muscle fiber is restimulated after it has completely relaxed – second twitch is of same magnitude as first twitch

54
Q

What is summation?

A

muscle fiber is restimulated before it has completely relaxed – second twitch is added on to first twitch

55
Q

What is tetanus?

A

muscle fiber is stimulated so rapidly that it does not have opportunity to relax at all between stimulations – maximal sustained contraction (tetanus)

56
Q

What happens when tetanus ends?

A

muscle fatigue leads to relaxation of muscle

57
Q

What happens if ACh is constantly present at synaptic cleft?

A
  • muscle spasms

- ACh is degraded by AChE until another contraction needs to occur

58
Q

In skeletal muscle, are dihydropyridine receptors in contact with ryanodine receptors?

A

yes

59
Q

Skeletal Muscle Contraction Process

A

–

60
Q

What is the sliding filament model of contraction?

A

actin and myosin filaments overlap slightly

actin filaments slide along myosin, resulting in greater overlap and shortening of sarcomere → contraction

61
Q

Does the length of myofilaments (thick or thin) get shorter during contraction and/or relaxation?

A

no

  • during contraction, actin and myosin filaments slide along each other and make the whole sarcomere shorter

+ CAPS 301: Muscle, Bodily Fluid, Cardio (13 decks)

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