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Physiology I > Lecture 4( mucle contraction) > Flashcards

Lecture 4( mucle contraction) Flashcards

1
Q

How much tension is in a muscle fiber when no actin is overlapping the myosin filaments

A

zero

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2
Q

at what point is the tension in the muscle the greatest

A

when actin filaments completely overlap myosin (sarcomere about 2.2 mirometers) until acin filament tips touch (sarcomere about 2micrometers long)

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3
Q

what is the length of the sarcomere at max tension

A

2.2-2 micrometers

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4
Q

Epimysium

A

Connective tissue surrounding entire muscle

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5
Q

muscle

A

made up of multiple fascicles

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6
Q

perimysium

A

CT surrounding individual fascicle

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7
Q

Fascicle

A

a bundle of myofibers

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8
Q

Endomysium

A

Delicate connective tissue around each myofiber

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9
Q

Sarcolema (plasmalemma)

A

Cell membrane of the muscle fiber

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10
Q

Myofibril

A

A chain of sarcomeres within a myofiber

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11
Q

Myofilament

A

Actin and myosin filaments that make up a sarcomere

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12
Q

what are T-tubules

A

invaginations of the sarcolemma
lie close to cisternae of sarcoplasmic reticulum
form triads with cisternae
two per sarcomere

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13
Q

what are z discs (z lines)

A

anchor actin filaments

located at each end of a sarcomere

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14
Q

What are the I-bands

A

Composed entirely of actin

width changes during contraction

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15
Q

Does the width of the I bands change with contraction

A

Yes

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16
Q

What are the A-bands

A

Composed of actin and myosin

  • Think all filaments
  • width does not change during contraction
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17
Q

Does the width of the A-bands change with contraction

A

No

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18
Q

What are the H-bands

A

Composed entirely of myosin

width changes with contraction

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19
Q

does the width of the H bands change with contraction

A

Yes

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20
Q

What Is the length of the sarcomere when the H band disappears

A

about 2 micrometers long

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21
Q

what is the length of the sarcomere when the I-bands are absent

A

about 1.65 micrometers, this is when the z lines are smashed up against the myosin filaments

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22
Q

do filaments themselves change length

A

No

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23
Q

where are nuclei and mitochondria located in skeletal muscle

A

On the periphery of the cell

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24
Q

what signals the release of Ach into the synaptic cleft

A

opening of voltage-gated calcium channels and influx of calcium into the axon terminal

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25
Q

what is the function of Ach on the sarcolemma

A

They open ligand gated sodium channels (creation of a local potential)

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26
Q

what are the voltage-gated channels on T-tubules called

A

DHP (dihydropyridine-channels)

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27
Q

What is the function of Dihydropyridine channels?

A

They interact and open ryanodine receptors on the SR membrane

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28
Q

What does calcium bind to in muscle fibers

A

Troponin C

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29
Q

how much does calcium concentration in the cytosol increase by after calcium release by the SR

A

Calcium is increased from 0.1micromols per liter to about 10 micromoles per liter

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30
Q

a conformational change in troponin C moves what away from active sites on actin

A

Tropomyosin

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31
Q

what are DHP receptors

A

Dihydropyridine receptors
voltage-sensitive L-Type calcium channels
located on the T-tubules

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32
Q

How are DHP receptors arranged

A

in quadruplets

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33
Q

do Dihydropyridine (DHP) receptors contribute to cytosol calcium levels?

A

Yes. They do so both actively and passively
A minute amount of calcium flows into the cytosol via these channels
They also cause a conformational change in the ryanodine receptors which then release more Calcium from the SR

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34
Q

where are RyRs (Ryanodine receptors located)

A

on the cisternae of the SR

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35
Q

What is the function of ryanodine (RyRs) receptors

A

Allow calcium into the cytosol from the SR

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36
Q

What is the function of SERCA

A

Sarcoplasmic Reticulum Calcium ATPases

uses ATP to pump calcium back into the SR

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37
Q

What is Calsequestrin

A

in the SR maintains an optimum calcium concentration gradient to facilitate return of calcium to SR

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38
Q

what is preload

A

load on a muscle in the relaxed state (before it contracts)

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39
Q

The greater the preload does what to the tension

A

increases the amount of passive tension in the muscle

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40
Q

Preload generates what kind of tension in the muscle

A

Passive tension

41
Q

what is passive tension

A

The force of resistance a muscle has to an applied load

42
Q

What is afterload

A

load the muscle works against

43
Q

When does an isotonic contraction occur

A

When the muscle generates more force than the afterload

44
Q

when does an isometric contraction occur

A

when a muscle generates less force than the afterload

45
Q

What is an isotonic contraction

A

same tone

46
Q

What is an isometric contraction

A

same length

47
Q

What is passive tension

A

produced by the preload

48
Q

what is active tension

A

produced by cross bridge cycling

49
Q

what is total tension

A

sum of active and passive tension

50
Q

when does cross-bridge cycling begin

A

when free calcium is available and attaches to troponin

51
Q

is ATP required to form the cross-bridge linking to actin

A

No

52
Q

is ATP required to break the cross-bridge link with actin

A

Yes

53
Q

increased cross-bridges to actin filaments means what

A

greater force of contraction

54
Q

Do cross-bridges act independently of all others

A

yes

55
Q

what is located on the myosin heads

A

ATP-ase

56
Q

what is a sarcomeres resting length

A

about 2 micrometers

57
Q

Tension in a muscle decreases when it is stretched beyond what length

A

2.2 micrometers

58
Q

where is ATP required for muscle contraction

A

most is used for sliding filament mechanism
pumping of calcium ions from sarcoplam back into SR
pumping of sodium and potassium ions through the sarcolemma to reestablish resting potential

59
Q

what is the concentration of ATP in a muscle fiber

A

about 4mmol

enough to maintain contraction for 1-2 seconds

60
Q

how long can the concentration of ATP in a muscle fiber maintain contraction

A

about 1-2 seconds

61
Q

what is the purpose of phosphocreatine in muscles

A
  • Releases energy rapidly
  • Reconstitues ATP
  • ATP=Phophocreatine provides enough energy for 5-8 seconds of contraction
62
Q

ATP + phosphocreatine provides enough energy for how many seconds of contraction

A

about 5-8 seconds

63
Q

How long can glycolysis sustain contraction

A

about 1 minute

64
Q

what is a product of glycolysis in muscle contraction

A

lactic acid

65
Q

what provides more than 95% of all energy needed for long-term contraction

A

Oxidative metabolism

66
Q

What is Isometric contraction

A

contraction that occurs when there is an increase in tension but not in length

67
Q

what is isotonic contraction

A

Muscle length changes

- two types Eccentric and concentric

68
Q

what is eccentric contraction

A

type of isotonic contraction

- occurs when the muscle lengthens

69
Q

What is a concentric contraction

A

type of isotonic contraction

- occurs when the muscle shortens

70
Q

what determines the myofiber type

A

The innervating neuron

71
Q

how are muscle fibers classified

A

resistance to fatigue and speed of contraction

72
Q

Characteristics of Fast (white) muscle

A 
contract rapidly, but less endurance
fewer mitochondria
primarily use anaerobic respiration resulting in buildup of pyruvic and lactic acid
little myoglobin
larger concentration of ATPase
73
Q

Characteristics of Slow (Red) muscle fibers

A 
contract slowly but have more endurance
more mitochondria
primarily use aerobic respiration
more myoglobin
smaller concentration of ATPase
74
Q

Can number of myofibers be increased after birth

A

NO

75
Q

Can the number of myofibrils be increased after birth

A

yes

76
Q

What is lost muscle tissue replaced by

A

Scar tissue (fibrous connective tissue

77
Q

The mass of a myofiber and muscle may increase by what mechanism

A

increase in the number of MYOFIBRILS

78
Q

what type of muscle is the soleus mostly composed of

A

Dark (slow twitch)

79
Q

What type of muscle is the gastrocnemius mostly composed of

A

Light (fast twitch)

80
Q

what is a motor unit

A

a neuron ad the myofibers it innervates

81
Q

When a neuron fires does all of the myofibers in the motor unit contract

A

Yes

82
Q

what effect would increased number of motor units have

A

increased force of contraction

83
Q

What is summation

A

electrical events occur faster than mechanical events
increased speed in cycling
increases muscle tension
each additional spike adds to the effects of the previous spikes

84
Q

How does summation increase the rate of cycling

A

additional spike occurs before previous calcium ions have been returned to the SR. This increases the total amount of calcium ion in the cytosol and increases the rate of cycling between the myosin and actin cross-bridges

85
Q

what is tetany

A

Frequency of spikes is fast enough, that there is no time for a relaxation between spikes
- the muscle remains at maximal contraction

86
Q

what is the position of the fulcrum in a first-class lever system

A

in the middle

87
Q

Which direction do the in and out forces move in a first-class lever system

A

Opposite directions

88
Q

In what direction and position are the forces in a second-class lever system

A

In and out forces move in the same direction and on the same side of the fulcrum
example raisin the body onto the ball of the foot

89
Q

define a third-class lever system

A

effort (in-force) is in the middle
both in and out forces move the he same direction and are on the same side of the fulcrum
ex. lifting a weight in the palm of your hand

90
Q

what term refers to a chain of sarcomeres

A

Myofibril

91
Q

what sarcomeric band does not undergo a change in length during the contraction of skeletal muscle

A

A-band

92
Q

what sarcomeric band is composed entirely of actin filaments

A

I-band

93
Q

Dihydropyridine (DHP) channels are part of what structure

A

T-Tubules

94
Q

Ryanodine-sensitive calcium ion release channels are part of what structure

A

SR

95
Q

by what factor does calcium concentration in the cytoplasm increase after calcium is released by the SR

A

100

96
Q

What maintains an optimum calcium concentration gradient to facilitate return of calcium to SR

A

Calsequestrin

97
Q

Are fast twitch muscle fibers more fatiguable than slow twitch

A

Yes

98
Q

Give an example of eccentric contraction

A

The triceps muscle while lowering the body to the floor during a push-up

Physiology I (8 decks)

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