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DEN 7101S Human Structure and Function II > 1/8 Howard Muscle Contraction > Flashcards

1/8 Howard Muscle Contraction Flashcards

1
Q

What are the 3 muscle cell types?

A
  • Cardiac
  • Skeletal
  • Smooth
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2
Q

What is the force of a muscle contraction generated by?

A

Interaction of actin and myosin

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3
Q

Muscle contraction requires:

A

Transient elevation of intracellular Ca2+

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4
Q

A muscle cell is also called:

A

Muscle fiber

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5
Q

Muscle cell is living or dead?

A

It is alive

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6
Q

Components of skeletal muscle fiber

A
  • Sarcolemma (plasma membrane)
  • Sarcoplasmic reticulum (SR)
  • Mitochondria
  • Myofibrils
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7
Q

What is the intracellular organization of myofibrils?

A
  • Many myofilaments form myofibril
  • Many myofibrils within a skeletal muscle fiber
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8
Q

Myofilaments in skeletal muscle

What are the thin strands?
What are the thick strands?

A
  1. actin (2 strands)
  2. myosin (1 thick strand)
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9
Q

Components of troponin

A

TnT, TnC, TnI

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10
Q

_____ binds tropomyosin

A

TnT

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11
Q

_____ binds calcium ions

A

TnC

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12
Q

_____ inhibits actin and myosin interaction

A

TnI

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13
Q

3 components of muscle contraction

A
  • excitation/contraction coupling
  • unmasking myosin binding site
  • sliding filament theory
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14
Q

What are the two components of excitation-contraction coupling?

A
  • Electromechanical coupling
  • Electrochemical coupling
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15
Q

Where is Ca2+ concentration the highest?

A

In the ER lumen

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16
Q

What is the T-tubule?

A

Transverse tubule; invagination of the sarcolemma among the myofibrils

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17
Q

what do T-Tubules facilitate?

A

Conduction of waves of depolarization (propagates action potential)

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18
Q

Where do T-Tubules lie in skeletal muscle?

A

in the plane of the A-I junction in mammalian skeletal muscle

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19
Q

Sarcoplasmic reticulum

A

Muscle SER

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20
Q

Key role of SR

A

Regulation of [Ca2+] (stores)

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21
Q

Explain the steps of excitation/contraction coupling

A
  • AP reaches NMJ
  • Vesicles containing Ach fuse with membrane
  • Releases Ach into synaptic cleft
  • Ach binds Ach receptor
  • Opens ion channels (sodium in, K+ out)
  • Triggers voltage-gated sodium channels
  • Action potential propagates to T-tubules
  • Reaches triad
  • [Ca2+] increases
  • contraction
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22
Q

What is DHPR in a skeletal muscle cell?

A

dihydropyridine receptor - voltage sensor

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23
Q

What is RyR in a skeletal muscle cell?

A

ryanodine receptor-calcium release channel

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24
Q

A triad is found in _____ and is comprised of _____

A

Skeletal muscle; 2 adjacent terminal cisternae and one T-tubule

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25
Q

During electromechanical coupling, skeletal muscle contraction allows for direction interactions between _____ and _____. This induces a _____ which releases ______

A

DHPR in T-tubule and RYR in the SR; conformational change; Ca2+

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26
Q

Skeletal muscle contraction is an example of ______ coupling

A

Electromechanical coupling

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27
Q

To unmask the myosin binding site, Ca2+ binds to ____ and causes ____

A

Troponin; tropomyosin to move away from the myosin binding site

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28
Q

Low cytosolic Ca2+ means that the muscle is _____

A

Relaxed

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29
Q

Low cytosolic Ca2+ in a skeletal muscle cell causes:

A
  • myosin binding sites are hidden
  • Energized cross-bridge cannot form (cannot bind to actin)
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30
Q

What occurs when cystolic Ca2+ levels are high in a skeletal muscle cell?

A
  1. Ca2+ binds to troponin causing tropomyosin to move AWAY from the myosin-binding sites
  2. Myosin binding sites are exposed
  3. Myosin binds to myosin binding sites on actin, forming a cross-bridge
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31
Q

What are the 3 components of sliding filament theory?

A
  1. ATP hydrolysis
  2. Cross bridge formation
  3. Power stroke
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32
Q

Explain the steps of sliding filament theory (diagram shown)

A
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33
Q

What are the components of the sarcomere?

A
  • Z lines
  • A band
  • H band
  • I band
34
Q

A sarcomere is defined as:

A

Z line to Z line

35
Q

What is the A band?

A

Actin and myosin overlap

36
Q

What is the I band?

A

Actin only

37
Q

What is the H band?

A

Myosin only (middle)

38
Q

During muscle contraction, what happens to the H band?

A

Disappears (he gone)

39
Q

During muscle contraction, what happens to the I band?

A

Narrows (an I is skinny and narrow)

40
Q

During muscle contraction, what happens to the Z lines?

A

Gets closer

41
Q

During muscle contraction, what happens to the A band?

A

Nothing; remains unchanged

42
Q

How does the sarcoplasmic reticulum of cardiac muscle compare to skeletal muscle?

A
  • SR is less extensive
  • Not enough stored Ca2+
43
Q

In cardiac muscle, what kind of filaments and what bands are presents?

A

Thick and thin filaments; alternating A and I bands

44
Q

Name some features of Skeletal Muscle T-tubules

A
  • T-Tubules lie in plane of A-I junction
  • Dilated terminal cisternae
  • Triad=2 terminal cisternae + 1 T Tubule
45
Q

Name some features of cardiac muscle T-tubules

A
  • T-tubules 2.5x larger (compared to skeletal muscle)
  • SR terminals approximate T-Tubules
  • Diad instead of traid
  • Diads at Z band
46
Q

Explain the steps of calcium-triggered calcium release:
1. Current spreads through _____ to contractile cells
2. action potentials travel along ____ and _____
3. What channels open and where?
4. What induces Ca2+ release from the SR?

A
  1. gap junctions
  2. plasma membrane and T tubules
  3. Ca2+ channels open in plasma membrane and SR
  4. Ca2+ induces Ca2+ release from SR
47
Q

What is unique about calcium release in cardiac muscle?

A

Calcium triggered calcium release

48
Q

What kind of coupling is Ca2+ induced Ca2+ release?

A

Electrochemical coupling

49
Q

What establishes coupling mode in cardiac muscle?

A

DHPR isoform

50
Q

In cardiac muscle, DHPR functions as:

A

Voltage-gated Ca2+ channel

51
Q

Schematic of Ca2+ induced release of Ca2+ (go through and describe what is happening)

A

(practice going through diagram)

52
Q

Smooth muscle:
1. Are striations present?
2. are T-tubules present?
3. voluntary or involuntary contraction?
4. how many nuclei present and where are they located in the cell?

A
  1. no (no paracrystalline structure)
  2. no
  3. involuntary
  4. 1 nuclei in center
53
Q

____ is used for involuntary contraction in the ANS, hormonal, and local control

A

Smooth muscle

54
Q

Shape of smooth muscle cells

55
Q

What filaments are present in smooth muscle?

A

Thick and thin filaments

56
Q

Smooth muscle is arranged in?

A
  • Sheets
  • Various thicknesses
  • Continuous network
  • Usually 2 layers perpendicular for peristalsis
57
Q

What are the thin filaments present in smooth muscle?

A

Actin and caldesmon

58
Q

What is caldesmon?

A

Protein in smooth muscle that blocks the active site of F-actin

59
Q

True or false: like skeletal and cardiac muscle, smooth muscle contains tropomyosin and troponin

A

False - neither

60
Q

What is the difference between smooth muscle myofilaments and skeletal?

A

Structural differences

61
Q

Smooth muscle myofilaments are arranged in:

A

Interwoven array; dense bodies act as Z disks

62
Q

Smooth muscle - myosin
1. heavy ________ (S1) project from the thick filaments whole length
2. the two ends lack ____
3. the middle has ______
4. _____ surface area for the interaction of actin with myosin II and permitting contractions of ______

A
  1. meromyosin heads
  2. heads
  3. heads
  4. larger; long duration
63
Q

Smooth muscle contraction
1. dependent on ____
2. control different than _______
3. What is absent?
4. ________ different conformation
5. actin-binding site is masked by ends of _________

A
  1. Ca2+
  2. striated muscles
  3. no troponin
  4. myosin II
  5. meromyosin
64
Q

Steps of smooth muscle contraction

A
  1. Calcium ions from caveolae and SR bind to calmodulin
  2. Binds caldesmon, unmasking active site on actin
  3. Ca2+-calmodulin complex activates myosin light chain kinase
  4. Myosin light chain kinase phosphorylates one of the myosin light chains
  5. Unfolds light meromyosin moiety
  6. Form the typical golf club-shaped myosin molecule
  7. Unmasks actin binding site
  8. Permits interaction between actin and myosin
  9. Contraction
65
Q

Where is smooth muscle found?

A

GI, vascular system

66
Q

What 3 signals contribute to a smooth muscle contraction?

A

Mechanical, electrical, and chemical signals

67
Q

Mechanical stretching in smooth muscle is _____

68
Q

Smooth muscle has what type of calcium channels?

A

L-type calcium channels

69
Q

What neurotransmitters are involved in smooth muscle contraction?

A

NE
Angiotensin
Vasopressin
Endothelin-1
thromboxane

70
Q

MLCK

A

Myosin light chain kinase

71
Q

MLCK is responsible for:

A

Phosphorylating myosin light chain

control if contraction occur or no cross-bridge activity

72
Q

Smooth muscle: relaxation
1. reduced ________ of MLC
2. reduced release of _____ by the SR or reduced ______ entry into the cell
3. inhibition of _______ by increased intracellular concentration of _______
4. increased ________ of activated myosin

A
  1. phosphorylation
  2. Ca2+, Ca2+
  3. MLCK, cAMP
  4. dephosphorylation (MLCP)
73
Q

_____ is used for calcium control in skeletal muscle

A

Calsequestrin in terminal cisternae

74
Q

_____ is used for calcium control in cardiac muscle

A

Calcium from extracellular sources

75
Q

_____ is used for calcium control in smooth muscle

76
Q

____ is used for calcium binding in skeletal muscle

A

TnC (troponin)

77
Q

____ is used for calcium binding in cardiac muscle

A

TnC (troponin)

78
Q

____ is used for calcium binding in smooth muscle

A

Calmodulin

79
Q

Nerve fibers are _____ in skeletal muscle

A

Somatic motor

80
Q

Nerve fibers are _____ in cardiac muscle

81
Q

Nerve fibers are _____ in smooth muscle

DEN 7101S Human Structure and Function II (21 decks)

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