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258 midterm > contraction and excitation of skeletal m. > Flashcards

contraction and excitation of skeletal m. Flashcards

1
Q

what are the 2 types of filament involved in the contraction of skeletal m.

A

actin and myosin

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2
Q

what do skeletal muscles surround and whats are they composed of

A

muscles that surround the skeleton (bones)
composed of numerous m. fibers(or m. cells)

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3
Q

what are m. fibers, what are they innervated by and what do they do

A

excitable cells that generate and propagate action potentials
are innervated by nerve fibers (motor neurons) to cause m. contraction

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4
Q

one n. fiber usually innervates ____ = ____

A

multiple m. fibers
=motor unit

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5
Q

which disease is characterized by the degeneration of alpha motorneurons in the spinal cord and brain stem

A

amyotrophic lateral sclerosis

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6
Q

each ____ contains several hundred to several thousand ____

A

m. fiber (cell), myofibrils

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7
Q

what is the mem of the muscle fiber that surrounds myofibrils

A

sarcolemma

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8
Q

each myofibril is composed of __ ___ elements called ____ (proteins)

A

2 contractile, myofilaments

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9
Q

what are the two myofilaments

A

thick filament: myosin
thin filament: actin

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10
Q

what is the biggest to the smallest unit in a m.

A

m > m. fiber > myofibril > actin/myosin

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11
Q

where does the contraction take place

A

in the sarcomeres

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12
Q

what are the smallest contractile unit of m. fibers (2 micrometers during contraction)

A

sarcomeres

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13
Q

what is aligned end to end in myofibrils and are separated by Z discs

A

sarcomeres

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14
Q

what causes the actin filaments to slide inwards among the myosin filaments

A

forces generated by the interaction btw the 2 filaments= power stroke

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15
Q

what happens to the actin filaments during m. contraction

A

the actin filaments are pulled by the myosin filaments inward toward the center of the sarcomere

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16
Q

is there any E required for the sliding filament mechanism

A

ATP which is converted into ADP+ Pi

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17
Q

are the actin filaments overlapping in the contracted or relaxed state

A

contracted, they don’t touch in the relaxed state

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18
Q

what are myosin composed of

A

body and cross-bridges(head and arm)

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19
Q

what are the actin filaments composed of

A

actin, tropomyosin and troponin

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20
Q

what is tropomyosin

A

a mol that hides the active sites (during relaxation)

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21
Q

what is troponin

A

a mol that moves tropomyosin from the active sites

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22
Q

what is the interaction btw actin and myosin filaments in a relaxed state

A

active sites on the actin filaments are covered by tropomyosin

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23
Q

what is the interaction btw actin and myosin filaments during m. contraction

A

-Ca2+ is released and Ca2+ ions bind on troponin
-troponin undergoes a conformational change, moving away the tropomyosin and uncovering the active sites
-myosin cross-bridges (heads) are attracted to the active sites of the actin

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24
Q

describe the first step of cross-bridge cycling

A
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25
Q

describe the second step of cross-bridge cycling

A
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26
Q

describe the third step of cross-bridge cycling

A
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27
Q

describe the fourth step of cross-bridge cycling

A
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28
Q

describe cross bridge cycling

A

1-ATP binds to myosin making it detach from actin
2-ATP turns into ADP, releasing E to convert myosin heads into cocked state
3-Calcium binds to troponin, which exposes sites on actin that myosin can grab
4-myosin then completes a power stroke, pushing on the actin

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29
Q

what is a muscle twitch (contraction)

A

is the tension developed in response to one n. stimulation

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30
Q

what is summation

A

means the adding together of individual m. twitches to increase the intensity of overall m. contraction

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31
Q

what are the 2 ways to reach summation (can also be less)

A

multiple fiber summation: increase the number of motor units contracting at the same time (recruitement)

frequency summation: increasing the frequency of stimulation of 1 motor unit

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32
Q

what is the size principle

A

depending on the intensity of the stimulation, motor units are recruited in an orderly fashion according to their size

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33
Q

which motor units are recruited first and for what kind of stimulation

A

smallest motor units are recruited first for weak stimulation
largest motor units are recruited last for strong stimulation

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34
Q

what allows the size principle for m. force

A

it allows the gradation of m. force from small steps (weak contraction) to great steps (Strong contraction)

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35
Q

what happens to the individual twitches when the frequency of signals increase

A

they summate bc of no recovery from previous contractions

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36
Q

what happens to the individual twitches when the frequency reaches a critical level

A

the summated twitches fuse together to form one continuous contraction (tetanization)

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37
Q

what happens during tetanization (to contraction and to Ca2+ ions)

A

contraction reaches a max level, no response to further stimulations
Ca2+ ions are maintained in the sarcoplasm, the contractile state of the muscle is sustained (myosin and actin stay attached)

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38
Q

what is an example of a sustained contractile state of the m.

A

crouching or holding up a heavy box (can lead to cramps, spasms)

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39
Q

m. fibers are innervated by ____ to cause ___

A

n. fibers (motor neurons)
m. contraction

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40
Q

one ___ ___ innervates multiple ___ = ____

A

n. fiber innervates multiple m. fibers=motor unit

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41
Q

describe small m. (what do they require, e.g, innervation ratio, n. innervates ___ m. fibers)

A

require precision
hand and eye
low innervation ratio
1n. innervates 2-3 m. fibers

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42
Q

describe large m. (what do they require, e.g, innervation ratio, n. innervates ___ m. fibers)

A

doesn’t require precision
gastrocnemius
high innervation ratio
1n. innervates 1000-2000 m. fibers

43
Q

describe slow fibers

A

-type 1, red m.
-smaller than fast fibers
-innervated by smaller n. fibers
-have a more extensive blood vessel system and more capillaries to supply extra amounts of O2
-have more mitochondria to support high levels of oxidative metabolism

44
Q

describe fast fibers

A

-type 2, white m.
-larger for greater strength of contraction
-an extensive sarcoplasmic reticulum is present for rapid release of Ca2+ to initiate contraction
-large amounts of glycolytic enzymes are present for rapid release of energy
-less extensive blood supply and fewer mitochondria vs slow fibers

45
Q

what is the contraction speed for type 1 (slow oxidative), type 2A (fast oxidative glycolytic) and type 2B (fast oxidative glycolytic)

A

type1: slow (100 ms)
type 2A: fast (50ms)
type 2B: fast (25ms)

46
Q

what is the fatigue rate for type 1 (slow oxidative), type 2A (fast oxidative glycolytic) and type 2B (fast oxidative glycolytic)

A

type1: slow
type 2A: intermediate
type 2B: fast

47
Q

what is the diameter for type 1 (slow oxidative), type 2A (fast oxidative glycolytic) and type 2B (fast oxidative glycolytic)

A

type1: small
type 2A: intermediate
type 2B: large

48
Q

what is the aerobic capacity for type 1 (slow oxidative), type 2A (fast oxidative glycolytic) and type 2B (fast oxidative glycolytic)

A

type1: high
type 2A: intermediate
type 2B: low

49
Q

what is the anaerobic capacity for type 1 (slow oxidative), type 2A (fast oxidative glycolytic) and type 2B (fast oxidative glycolytic)

A

type1: low
type 2A: intermediate
type 2B: high

50
Q

what types of fibers are human muscles made of

A

genetically determined mixture of both slow and fast type fibers

51
Q

in most muscles used for mvt on average: __ % slow fibers and __%fast fibers

A

50/50

52
Q

how would you describe speed and strength of contraction of muscle fibers

A
53
Q

which of the two has more slow twitch fibers than fast twitch fibers: sprinters or marathon runners

A

marathon runners

54
Q

can exercise training change muscle fiber types

A

yes but very limited changes (± 10%)

55
Q

t/f fibers cannot change from type 2A to type 2B

A

false, they can change within their own types only

56
Q

what is unknown about fiber types

A

IT IS UNKNOWN WHETHER:
-muscle types are more malleable early in life
-certain m., like the biceps, are more adept at changing fiber types than others
-muscle fibers can truly change btw type 1 and type 2 and how long it takes to do so

57
Q

most studies thus far have examined the effects of exercise on muscle fiber types over just ___ to __ ___. In addition, we still don’t know the exact mechanism behing __ ___ _____, though some researchers believe it has to do with the ___ that ___ the m.

A

5 to 6 months
fiber type conversion
nerve, activates

58
Q

why do you think soleus and gastrocnemius muscles have a greater % of slow twitch vs fast twitch fibers

A

to sustain prolonged periods of standing and walking

59
Q

specify which fibers are used in each:
walking
lifting a sofa
lifting a sofa whilst going up stairs

A

type 1
type 2A
type 2B

60
Q

what is another name for neuromuscular junction

A

motor end plate

61
Q

what is a neuromuscular junction (contact btw what and what, equivalent to what, where do the n. terminals go, what is the released neurotransmitter)

A

-contact btw n. terminals (branching from motor neuron axon) and m. fiber plasma mem (sarcolemma)
-equivalent of chemical synapse in the CNS
-n. terminals invaginates into the surface of the m. fiber
-acetylcholine

62
Q

what are the steps at the neuromuscular junction

A

1-AP arrives at presynaptic terminal
2-Local depolarization opens voltage gated Ca2+ channels and Ca2+ ions flow into terminal
3-Ca2+ ions trigger the fusion of synaptic vesicles with the presynaptic mem
3-release of the NT into synaptic cleft (exocytosis)

63
Q

at the nmj; m. fiber mem has ___ receptors that contain ___ channels (___, ___)

A

acetylcholine
cation
(Na+, K+)

64
Q

ACh mol attach to what in the m. fiber mem

A

binding sites

65
Q

what happens when the cation channels open

A

-positive ions (Na+, K+, Ca2+) flow thru channels
-but far more Na+ ions flow inside

66
Q

how many Na+ ions in 1 ms can 1 Na+ channel transmit

A

15 000 to 30 000 Na+ ions

67
Q

the entry of the Na+ ions creates what

A

an end plate potential (equivalent to EPSP)

68
Q

what does the endplate pot initiate

A

AP

69
Q

where are we here

A

n. terminals and myofibrils

70
Q

what is sarcoplasmic reticulum

A

-surrounds myofibrils as a net
-contains Ca2+ (necessary for m. contraction process)
-contains voltage-sensitive Ca2+ receptors (diffusion of Ca2+ into the sarcoplasm)
-contains a Ca2+ pump to remove the Ca2+ from the sarcoplasm

71
Q

what are T-tubules (transverse tubules)

A

-begin at cell mem (sarcolemma) and penetrate all the way from one side of the mem to the opposite side
-run transverse to myofibrils
-are in contact with the sarcoplasmic reticulum
-for easy propagation of APs inside the m. fiber (rich w Na+/K+ channels)

72
Q

what is the first step of the neuromuscular transmission and excitation-contraction coupling

A

AP arrives at the axon terminal and causes the release of ACh on the synaptic cleft. ACh binds to receptors on the sarcolemma and activates cation (Na+) channels

73
Q

what is the second step of the neuromuscular transmission and excitation-contraction coupling

A

Net entry of Na+ initiates an AP which is propagated along the sarcolemma and down the T tubules

74
Q

what is the third step of the neuromuscular transmission and excitation-contraction coupling

A

AP in T tubule activates voltage-sensitive receptors, which in turn trigger Ca2+ release from sarcoplasmic reticulum into sarcoplasm

75
Q

what is the fourth step of the neuromuscular transmission and excitation-contraction coupling

A

Ca2+ ions bind to troponin; troponin changes shape, removing the blocking action of tropomyosin; actin active sites exposed

76
Q

what is the fifth step of the neuromuscular transmission and excitation-contraction coupling

A

cross-bridge cycling: myosin heads alternately attach to actin and detach pulling the actin filaments towards the center of the sarcomere; release of energy by ATP hydrolysis powers the cycling process

77
Q

what is the sixth step of the neuromuscular transmission and excitation-contraction coupling

A

removal of Ca2+ by a Ca2+ pump (active transport, ATP) from sarcoplasmic into the SR after the AP ends

78
Q

what is the seventh step of the neuromuscular transmission and excitation-contraction coupling

A

without Ca2+, tropomyosin blockage restored (blocking myosin heads to attach to the active sites of actin); contraction ends and m. fiber relaxes

79
Q

what is myasthenia gravis

A

neuromuscular disease caused by an auto-immune response: antibodies block or destroy ACh receptors

80
Q

what are the symptoms of MG

A

m. weakness, that develops progressively across the day (worse towards the end of the day)
affects facial m. (eyelid drooping), limb m., respiratory m. ,etc.

81
Q

what is the tx for MG

A

immunosuppressant tx
symptomatic tx: acetylcholinesterase (enzyme that catalyzes the breakdown of ACh) inhibitors

82
Q

what is the cause for rigor mortis and when does it occur

A

body rigidity due to substained m. contraction after death
occurs within the first day (3-12 hours), and decreases gradually (depending on the ambient temperature; cold slows
the process down)

83
Q

what mechanisms cause rigor mortis

A

Lack of ATP,
Ca2+ pump cannot transport Ca2+ back into the sarcoplasmic reticulum, thus Ca2+ keeps the actin active sites continuously exposed
myosin head cannot detach from actin (needs ATP)

84
Q
A

1- myofibrils
2- Z disk
3- sarcolemma
4- terminal cisternae
5- sarcoplasmic reticulum
6- transverse tubules

85
Q

describe each letter

A

point D: actin filament has pulled all the way out to the end of myosin filaments, no tension
point C: sarcomere shortens and actin filament begins to overlap myosin, Tension increases until sarcomere reaches 2.2 micrometers
point B: sarcomere maintains full tension
point A: the end of actin filaments overlap each other. As the sarcomere length decreases from 2.0 micrometers down to 1.65 micrometers, the strength of contraction decreases rapidly

86
Q

what is active tension

A

interaction btw myosin heads and actin filaments determines the tension; when m. is stimulated to contract
due to overlapping of actin and myosin heads
involves E (ATP)

87
Q

what is passive tension

A

when m. fibers are pulled apart (no contraction)
stretching
tension/force generated in absence of E (no ATP) when m. fibers are pulled apart (e.g stretching fingers after stroke, MS, arthritis)

88
Q

what is total tension

A

summation of passive and active tension

89
Q

what are each of the lines

A

red is active tension
blue is passive tension
purple is total tension

90
Q

what comprises the passive structures that elongate elastically

A

titin (inside m. cell)
collagen (surrounding m. cell)

91
Q

what is titin

A

protein believed to be the greatest contributor to passive force throughout normal ranges of motion
connects the Z disk to the M line in the sarcomere
limits the range of motion of the sarcomere in tension, thus contributing to the passive stiffness of muscle

92
Q

examples of increase in active and passive stiffness of hand m.

A

hand contracture after immobilization due to forearm fracture
hand contracture due to spasticity (neurological condition)

93
Q

what is the resting length

A

the length at rest from which a muscle develops MAXIMUM isometric tension

94
Q

m. tension is dependent on what

A

muscle length; the more flexible a person, the longer a m. can be stretched

95
Q

when a m. becomes more flexible (as a result of stretching), what happens to the passive tension curve

A

it moves to the right of the graph

96
Q

maximum strength of contraction of a muscle operating at a normal length averages ___

A

3.5 kg/cm2 (sq. cm) of m.

97
Q

since a quad m. can have up to 103 cm2 of m. belly, as much as ___ can be applied to the patellar tendon

A

360.5 kg

98
Q

describe ocular movement

A

ocular mvt must be extremely rapid to maintain fixation of the eyes on specific objects to provide accuracy of vision

99
Q

describer gastrocnemius movement

A

gastroc must contract moderately rapidly to provide enough velocity of limb mvt for running and jumping

100
Q

describe soleus mvt

A

soleus is concerned maily w slow contraction for continual, long term support of the body against gravity

101
Q

what is m. hypertrophy

A

increase in total m. mass

102
Q

what causes m. hypertrophy

A

-results from an increase in number of actin and myosin filaments in each m. fiber, causing enlargement of the individual m. fibers
-caused when the m. is loaded during the contractile process

103
Q

what is required to cause significant hypertrophy

A

only a few strong contractions each day for 6 to 10 weeks

104
Q

what are the training effect of m. hypertrophy

A

-nb of actin and myosin filaments in myofibrils can increase by as much as 50%
-myofibrils can split to form new myofibrils and increase fiber and muscle size

258 midterm (6 decks)

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