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Cell Bio Exam 2 > Muscle > Flashcards

Muscle Flashcards

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1
Q

What are the different types of myofilaments (muscle filaments)?

A 
thin filament (actin, troponin, tropomyosin)
thick filaments (myosin II)
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2
Q

What are the 3 connective tissue wrappings of skeletal muscle tissue?

A

endomysium
perimysium
epimysium

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3
Q

What are the three structural components of skeletal muscles?

A

T-tubules
Terminal cisternae
Triads

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4
Q

What are the four structural components of cardiac muscles?

A
  • T-tubules
  • Dyads
  • Intercalated discs (transverse and lateral portions)
  • Purkinje fibers
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5
Q

What are the three structural components of smooth muscles?

A
  • gap junctions
  • dense bodies
  • caveolae
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6
Q

Muscle contraction is mediated by which myofilaments?

A

thin and thick filaments

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7
Q

What does actin consist of?

A
  • globular actin (G-actin monomers)
  • 2 G-actin polymers twist to form a double-stranded helix (spiral) - filamentous actin
  • Filamentous actin (F-actin)
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8
Q

What are the three subunits of troponin?

A

1) TnT - (T for tropomyosin) subunit attaches to tropomyosin
2) TnC - (C for calcium) subunit binds calcium ions
3) TnI - (I for inhibition) binds troponin complex to actin (inhibits actin-myosin interaction)

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9
Q

What is the contractile unit of striated muscle?

A

sarcomere (thick and thin filaments)

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10
Q

What does G-actin also known as?

A

Globular actin monomer

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11
Q

What do the G-actin assemble to form?

A

G-actin assembles to form a poly (string of beads)

- two polymers twist together to form filamentous actin

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12
Q

What is the main protein component of thin filaments?

A

actin

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13
Q

What does tropomyosin consists of?

A

two polypeptide chains that come together to form an alpha helix

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14
Q

What does tropomyosin rest on?

A

Each alpha helix rests on 7 G-actin monomers, covering the active site of monomers to prevent actin/myosin interaction
- the molecules are attached to each other in a head-to-tail manner, coming together to form a filament

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15
Q

What makes up the thin filaments of striated muscle?

A

filamentous actin
troponin molecules
filamentous tropomyosin

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16
Q

What does the myosin molecule consist of?

A

2 heavy chains (golf clubs)

4 light chains

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17
Q

What breaks a myosin molecule into two segments?

A
  • trypsin

- into heavy and ligh meromyosin

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18
Q

What are the components of heavy meromyosin?

A

4 light chains
2 globular heads
a short twisted tail (alpha-helical config.)

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19
Q

What are the components of light meromyosin?

A

2 chains wrapped around each other in an alpha-helix to make a long twisted tail

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20
Q

What can heavy meromyosin be broken down into?

A

broken down by papain
2 S1 moieties (each S1 = 2 light chains + 1 globular head)
1 S2 segment (short twisted tail)

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21
Q

Describe the layers of a muscle cell

A
  • overlapping thin filaments + thick filaments form a sacromere
  • long cylindrical series of end-to-end sacromeres form a myofibril
  • many parallel myofibrils are enclosed within a muscle fiber
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22
Q

In the relaxed state, a sacromere exhibits…

A 
A-band
H-band
I-band
Z-line (discs)
M-line
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23
Q

What is the A-band?

A

dark band of thick and thin filaments

- widest band of sacromere

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24
Q

What is the H-band?

A

consists of thick filaments only

- bisects the A-band

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25
Q

What is the I-band?

A

light band of thin filaments

- made up of portions of adjacent sarcomeres

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26
Q

What are the Z-discs?

A
  • attachment for thin filaments
  • contain alpha-actinin that anchors actin filaments to the Z-disc
  • bisects the I-band
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27
Q

What is the M-line?

A
  • consists of protein structures lying between thick filaments, holding them in register
  • creatine kinase is the major protein
  • bisects H-band
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28
Q

What accessory protein anchors thick filaments to Z-discs?

A

titin (elastic protein)

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29
Q

What accessory protein anchors thin filaments to Z-discs that’s also a component of Z-disc?

A

alpha-actinin

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30
Q

What accessory protein anchors thin filaments to Z-disk and wraps around each thin filament?

A

2 molecules of nebulin, nonelastic protein

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31
Q

What two accessory proteins secure thick filaments in register at the M-line?

A

myomesin and C protein

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32
Q

What cytoplasmic protein binds actin (thin) filaments to laminin (component of the external lamina surrounding the muscle fiber)

A

dystrophin

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33
Q

What are the components of a skeletal muscle cell?

A

1) sarcolemma
2) nuclei
3) sarcoplasm
4) organelles
5) sarcosomes
6) myofibrils
7) sarcoplasmic reticulum
8) myoglobin
9) glycogen

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34
Q

What is the sarcolemma composed of?

A

cell membrane + external lamina + reticular lamina

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35
Q

What is the muscle cell cytoplasm called?

A

sarcoplasm

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36
Q

What does the mitochondria of muscle cell called?

A

sarcosomes

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37
Q

What is the smooth endoplasmic reticulum called in muscle cells?

A

sarcoplasmic reticulum

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38
Q

What is endomysium?

A

reticular fibers that surrounds each muscle fiber (cell)

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39
Q

What is perimysium?

A

thin, collagenous connective tissue, derived from epimysium that surrounds a fascicle (bundle)

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40
Q

What is epimysium?

A

dense irregular collagenous connective tissue surrounds many fascicles “deep fascia”
- sends septa within the muscle so that vessels and nerve fibers may reach deeper aspects of the muscle

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41
Q

Which type of muscle is this?

  • contraction is rigorous and rhythmic, continuous
  • striated and involuntary
A

cardiac muscle

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42
Q

Which type of muscle is this?

  • non-striated and involuntary
  • contraction is weak and slow
A

smooth muscle

43
Q

Which type of muscle is this?

  • striated, striped and voluntary
  • contraction is quick and forceful, discontinuous
A

skeletal muscle

44
Q

What type of involuntary movement is smooth muscle responsible for?

A
  • pupillary constriction and dilation
  • accommodation of lens of eye
  • piloerection
  • peristalsis
  • blood vessel constriction and dilation
45
Q

Which type of muscle cells are specialized for contraction?

A

all types (skeletal, cardiac, and smooth muscle cells)

46
Q

Muscle cells contain an abundance of what type of filaments?

A

contractile (thin and thick) filaments

47
Q

Describe the nuclei of skeletal muscle cells.

A

oval-fusiform shaped and euchromatic

48
Q

Skeletal muscle fibers are covered by what?

A

external lamina and reticular fibers

49
Q

What part of skeletal muscle fibers store calcium in their lumen?

A

terminal cisternae

50
Q

What are transverse tubules (T-tubules)?

A

invaginations of the cell membrane (sarcolemma)

- lumen is continuous with the extracellular space and contain ECF

51
Q

What is the function of T-tubules?

A

carry nerve impulses deep into the cell

52
Q

What forms a “lacy” sleeve around each myofibril?

A

sarcoplasmic reticulum (SR)

53
Q

What makes up a triad in skeletal muscle cells?

A

1 T-tubule + 2 terminal cisternae of SR = triad at A-I junction of sarcomere

54
Q

What are satellite cells?

A

regenerative cells that lie between the skeletal muscle cell and its external lamina

55
Q

Briefly explain what satellite cells do following tissue injury.

A

1) undergo proliferation and differentiate into myoblasts
2) myoblasts assemble to form myotubes
3) myotubes form muscle tissue
* external lamina must be present and intact in order for myotubes to form

56
Q

What happens when external lamina is damaged?

A

fibroblasts will synthesize collagen and form scar tissue instead

57
Q

What is a motor unit?

A

lower motor neuron (nerve cell) and all the muscle fibers it innervates

58
Q

What is a motor end plate?

A

neuromuscular junction/ myoneural junction

  • axon terminal
  • synaptic cleft
  • muscle cell sarcolemma
59
Q

What is the presynaptic membrane of the motor end plate?

A

part of the axon terminal that contains synaptic vesicles filled with acetylcholine (Ach)

60
Q

What is the postsynaptic membrane of the motor end plate?

A

muscle cell sarcolemma

61
Q

What is Myasthenia Gravis?

A

autoimmune disease causing muscle weakness

62
Q

What is the etiology of Myasthenia Gravis?

A

autoantibodies are produced that bind to the Ach receptor protein on the sarcolemma of the skeletal muscle cell, forming an ab-receptor complex. This effectively blocks the Ach from binding to the sarcolemma, thus prevent muscle contraction and cause muscle weakness

the ab-receptor complexes are continuously destroyed (even newly develped ones) which decrease the number of receptor sites available on the sarcolemma, leading to progressive weakness

63
Q

What is muscular dystrophy?

A

X-linked recessive genetic, degenerative disease, affecting striated muscles
- symptoms include weakness and atrophy of the shoulder, hip, pelvic, and thigh muscles

64
Q

Describe the etiology of Duchenne muscular dystrophy (DMD)

A
  • most common and most severe muscular dystrophy
  • mutated dystrophin gene causing a null mutation (protein is absent)
  • dystrophin binds to cytoplasmic actin filaments in the inner surface of the muscle cell sarcolemma overlying the Z-discs of sarcomeres
65
Q

How are cardiac muscle cells attached?

A

end-to-end, to form muscle fibers of variable length (cells are short and branched)

66
Q

What do cardiac muscle cells have that can be converted to glucose for energy?

A

glycogen deposits

67
Q

What is the major fuel source for cardiac muscle cells?

A

fatty acids

- lipid droplets floating in cytoplasm that contain triglycerides that can be broken down

68
Q

What is lipofuscin?

A

aging pigment that are present in cardiac muscle cells of older individuals

69
Q

How many nuclei are in cardiac muscle cells and where are they located?

A

1-2, centrally located within cell

70
Q

What are atrial granules (membrane-bound granules)?

A

these granules are mostly located in muscle fibers of the right atrium and contain atrial natriuretic factor and brain natriuretic factor (diuretic hormones that act on kidneys to will result in water loss leading to lower blood pressure)

71
Q

What are each cardiac muscle fiber covered by?

A

endomysium rich with capillaries

72
Q

What makes up 40% of the cytoplasmic volume of cardiac muscle cells?

A

mitochondria

73
Q

What are intercalated discs?

A

specialized intercellular junctions (connections)

- transverse and lateral portions

74
Q

Where are the transverse portions of intercalated discs?

A

perpendicular to long axis of muscle fiber

75
Q

Where are the lateral portions of intercalated discs?

A

parallel to cell’s longitudinal axis

76
Q

Which portion of intercalated discs contain fascia adherens?

A
  • transverse

- anchor actin filaments of terminal sarcomere to plasma membrane

77
Q

Which portion of intercalated discs contain maculae adherens?

A
  • transverse
  • spot desmosomes
  • bind cells together
78
Q

Which portion of intercalated discs contain gap junctions?

A
  • lateral

- permit flow of ions from cell to cell so that muscle contracts as a syncytium

79
Q

What makes up a dyad in cardiac muscle cells?

A

1 T-tubule + 1 SR = dyad at Z-disc

**cardiac cells have small terminal cisternae

80
Q

What’s the function of Ti-tubules in cardiac muscle cells?

A

carry calcium from the extracellular space into the cardiac muscle cells
**T-tubules of ventricular muscle are larger and more abundant than those of skeletal muscle

81
Q

What are Purkinje fibers?

A

specialized cadiac muscle cells located in the endocardium

- large, pale staining cells, cytoplasm contains glycogen deposits, and few myofibrils

82
Q

What’s the function of Purkinje fibers?

A

act as “batteries” which relay electrical impulses to cardiac muscle fibers (not to amplify or enhance the contractile force)

83
Q

What forms the impulse-generating and conducting system of the heart?

A

SA node, AV node, bundle of His, and Purkinje fibers
- they relay electrical impulses to cardiac muscle fibers of the atria and ventricles to coordinate the contraction of the chambers

84
Q

Injury to heart muscle is repaired with what?

A

fibrous connective tissue

85
Q

What is a troponin test?

A

blood test that is specific to cardiac muscle tissue damage (troponin I or troponin T)

  • help diagnose a heart attack or other heart injury
  • test is ordered again at 6-12 hours after initial test
  • healthy individuals will have low troponin levels
86
Q

Do injury to skeletal muscles result in elevated troponin blood levels?

A

no, troponin blood test is specific to cardiac muscle cells

87
Q

What organs are smooth muscle found in?

A

pharynx, esophagus, stomach, small and large intestine, vessel wall, respiratory tract, urogenital system, skin, eye

88
Q

What are some differences between smooth muscle and skeletal or cardiac muscles?

A
  • smooth muscles are not striated (no sarcomeres)
  • contain thick and thin filaments, but no troponin
  • mononuclear (located in the center of cell)
89
Q

What type of interceullar junctions do smooth muscle cells have?

A

gap junctions

  • allowing ions to pass from cell to cell
  • involved in regulation of contraction
90
Q

How are myofilaments arranged in smooth muscle cells?

A

myofilament bundles criss-cross, forming dense bodies at points of attachment on the internal surface of the cell membrane

91
Q

What are the two types of dense bodies in smooth muscle cells?

A
  • membrane-associated

- cytoplasmic

92
Q

Where are membrane-associated dense bodies located?

A

they attach to the inner surface of the cell membrane

93
Q

Where are cytoplasmic dense bodies?

A

suspended in the cytoplasm

94
Q

What do both types of dense bodies contain that is similar to Z-discs?

A

alpha-actinin

95
Q

What do dense bodies do?

A

serve as attachment for thin filaments and intermediate filaments

96
Q

Which type of muscle cells form sheets?

A

smooth

97
Q

By what mechanism do smooth muscle contract?

A

sliding filament mechanism, similar to skeletal muscle

98
Q

Do smooth muscle cells contain T-tubules? What about sarcoplasmic reticulum (SR)?

A

No T-tubules and SR is not well developed

99
Q

What is caveolae?

A

pinocytotic vesicles that form bubble-like structures on the inner surface of cell membrane
- releases calcium ions into the cell for contraction

100
Q

Where are unitary smooth muscles found?

A

aka visceral

  • walls of intestines, ureters, uterus
  • have abundant gap junctions
101
Q

Where are multiunit smooth muscles found?

A

iris of the eye (sphincter and dilator pupillae muscles)

102
Q

What’s the difference between innervation of unitary and multiunit smooth muscles?

A

unitary - one nerve fiber innervates a few smooth muscle cells (poor innervation)
multiunit - each muscle fiber (not cell) has its own nerve supply, therefore can contract independently of each other (rich innervation)

103
Q

How do the ANS and hormones modify smooth muscles?

A

rate of contraction, but do not initiate it

- smooth muscle contracts spontaneously

104
Q

Review muscle contraction

A

Yep, that’s it

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