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Physiology > SK 1 Skeletal Muscle and Reflexes > Flashcards

SK 1 Skeletal Muscle and Reflexes Flashcards

1
Q

what is the anatomical organization of a skeletal muscle

A

-whole muscle
-muscle fascicles
-muscle fibers (cells)
-myofibrils
-myofilaments (thick and think) arranged in sarcromeres

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2
Q

what is a sarcomere

A

functional unit of cardiac and skeletal muscle

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3
Q

what is the dark band

A

the A band

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4
Q

what is the light band

A

the I band

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5
Q

what creates the striated appearance in skeletal and cardiac muscle

A

alternating A bands and I bands

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6
Q

what happens to the I band, the H zone and the A band in muscle contraction

A

I band: shortens
H zone: shortens
A band: stays the same

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7
Q

what does the I band contain

A

thin filaments

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8
Q

what does the A band contain

A

entire length of thick filaments

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9
Q

what does the H zone contain

A

only thick filaments

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10
Q

what is anchored at the Z line

A

thin filaments

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11
Q

what does the M line link

A

the central regions of thick filaments

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12
Q

how do sarcomeres change in length during contraction

A

they shorten

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13
Q

what is the thin filament composed of

A

actin, tropomyosin and troponin

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14
Q

what does actin contain

A

G-actin molecules, the active site that binds myosin

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15
Q

what does troponin bind

A

actin, tropomyosin and calcium

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16
Q

what regulates when contraction can happen

A

troponin and tropomyosin

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17
Q

what is the thick filament made of

A

myosin

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18
Q

what are the 3 globular proteins of troponin

A

T, C and I

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19
Q

what is the dystropin-glycoprotein complx

A

dystrophin protein connects thin filaments to glycoproteins in sarcolemma

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20
Q

what does the dystropin-glycoprotein complex do

A

provides scaffolding for sarcomeres

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21
Q

what are the types of muscular dystrophy

A

-duchenne
-beckers
-myotinic
-oculopharyngeal
-limb girdle

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22
Q

what is similar and different about duchennes MD and Beckers MD

A

similar: both produce less dystrophin
difference: duchennes produces much less dystrophin than beckers

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23
Q

what happens in myotonic MD, what type of inheritence and when is onset

A

muscle contracts and struggles to relax, autosomal dominant, most common form of MD in adult

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24
Q

what NT does the alpha motor neuron release and what does it bind to

A

releases AcH which binds to a nicotonic receptor on the muscle fiber

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25
Q

how does botox work

A

inhibits the release of ACH at the NMJ

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26
Q

what can botox be used for in dentistry

A

bruxism, sialorrhea, masseteric hypertrophy

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27
Q

what are the 3 phases of muscle twitch

A

latent, contraction, relaxation

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28
Q

what is the latent period of muscle twitch

A

time between AP and when muscle starts producing force

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29
Q

what is required to occur before contraction can happen

A

intracellular calcium in muscle fiber must increase

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30
Q

what does tropomyosin do in resting muscle

A

prevent a strong bond between the myosin head and G actin molecules

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31
Q

what happens when troponin binds to calcium

A

tropomyosin is pulled away from the myosin binding site and allows for the power stroke

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32
Q

what is calcium released from

A

sarcoplasmic reticulum

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33
Q

what are T-tubules and what do they do

A

invaginations of sarcolemma that allow for APs to be transmitted deep in the cell

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34
Q

what are terminal cisterna

A

portion of SR that contract T tubules

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35
Q

what is the mechanism of action of calcium release from the SR

A

AP travels down the membrane and T tubules and activates voltage sensitive dihydropyridine (DHP) receptors on the T tubules. these open calcium channels (ryanodine receptors) on the SR

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36
Q

what is the mechanism of action with ATP in muscle contraction

A

-ATP binding to the myosin head breaks the cross bridge between actin and myosin
- energy released from ATP hydrolysis by the myosin head provides energy for cocking the myosin head
- release of inorganic phosphate from the myosin head provides energy fr the power stroke which shortens the sarcomere

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37
Q

muscle cells only have enough ATP for ~ ___ twitches

A

8

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38
Q

what does the source of ATP in a muscle fiber depend on

A

-the metabolic enzymes are present in the cell (glycolytic vs oxidative fibers)
-the intensity of the exercise

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39
Q

what are the sources of ATP

A

-aerobic and anaerobic metabolism
- phosphocreatine

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40
Q

what does creatine kinase blood levels measure

A

if damage to muscle tissue has occurred

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41
Q

fatigued muscles:

A

-have decreased tension generation
- take longer to contract
- relax more slowly and may not completely relax

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42
Q

what are the theories for fatigue

A
  • change in membrane potential
    -decreased ACH
    -blockage of blood flow
  • central fatigue
  • increased metabolic byproducts (lactate)
    -depleted glycogen
43
Q

what must be present for cross bridge cycling

A

calcium AND ATP

44
Q

explain cross bridge cycling (sliding filament theory)

A

-rigor state: myosin and actin are tightly bound
-ATP binds myosin, decreases its affinity for actin and the two separate
-myosin head moves in the direction of the Z line, ATP is hydrolyzed
- myosin binds the next actin and power stroke occurs
-ADP is released and the actin and myosin resume the brief rigor state

45
Q

what is required to relax skeletal muscle

A

-alpha motor neuron must stop firing
- cytosolic calcium concentrations must decrease

46
Q

how do cytosolic calcium concentrations decrease to relax skeletal musclr

A

-calcium ATPases on SR remove calcium from cytosol
-tropomyosin moves and covers actins myosin binding site
- actin slowly slides back to its original resting place and the sarcomere returns to its original length

47
Q

why doesnt ATP need to be removed with calcium to relax skeletal muscle

A

ATP must be present to release myosin from actin

48
Q

what are the 3 types of skeletal muscle fibers

A

-slow twitch (type 1)
-fast twitch- oxidative glycolytic (type 2A) and glycolytic (type 2B)

49
Q

describe the color, glycolytic capacity, oxidative capacity and fatigue of type 1 fibers

A

color-red
-glycolytic capacity- moderate
-oxidative capacity-high
-fatigue- slow

50
Q

describe the color, glycolytic capacity, oxidative capacity and fatigue of type 2A fibers

A

color-red
-glycolytic capacity- high
-oxidative capacity-moderate
-fatigue- fast resistant

51
Q

describe the color, glycolytic capacity, oxidative capacity and fatigue of type 2B fibers

A

color-white
-glycolytic capacity- high
-oxidative capacity-low
-fatigue- fast fatigable

52
Q

how can skeletal muscle fibers change in response to use

A

in size and fiber types

53
Q

how do fibers change in size

A

hypertrophy, atrophy, sarcopenia

54
Q

what are human jaw closing muscle fiber types

A

mixture of type 1 and type 2 fibers, the type 2 fibers are much smaller than the type 1

55
Q

how does the jaw muscles change with age

A

thickness decreases and type 1 fibers number decreases and type 2 increase

56
Q

what is a motor unit

A

the alpha motor neuron and the muscle fibers it innervates

57
Q

what are motor units recruited in order of

A

size, small recruited first (type 1) but small motor units control fewer fibers

58
Q

what does an increase in the number of motor units activated increase

A

the total tension produced by contraction of a muscle

59
Q

what are small motor units composed of

A

slow twitch oxidative fibers

60
Q

which muscle fibers are the smallest

A

type 1

61
Q

which muscle fibers have the lowest threshold for firing

A

type 1

62
Q

what are larger motor units composed of

A

fast twitch glycolytic fibers

63
Q

what determines the type of contraction

A

the amount of load and the force the muscle generates

64
Q

what is isometric contraction and what is the result

A

force produced is less than the load resulting in no movement

65
Q

what is isotonic contraction and what is the result

A

force produced is great enough to move a load

66
Q

has the muscle shortened in isometric contraction

A

no, but sarcomeres shorten to generate force

67
Q

when does the contraction become isometric

A

when the muscle cannot move the load anymore

68
Q

what does the force of contraction do the cross bridges and force

A

increases both

69
Q

how do you increase total force

A

-increasing the frequency of fiber activation (AP)
-increasing the number of muscle fibers contracting (motor unit recruitment)

70
Q

for a single muscle twitch, the tension developed is altered by ____

A

sarcomere length

71
Q

what is optimal length

A

the best degree of overlap between thick and thin filaments
- greatest number of actin/myosin cross bridges can form resulting in maximal tension production

72
Q

what does the velocity of contraction depend on

A

the load a fiber is contracting against and the type of fibers

73
Q

the greater the load the ___ the speed of contraction

A

slower

74
Q

what are the skeletal muscle reflexes

A

-stretch reflex (muscle receptors)
- golgi tendon reflex (tendon receptors)

75
Q

what fibers are found in the muscle spindle

A

1a fiber (sensory) and A gamma (motor)

76
Q

what sensory fibers are found in the golgi tendon

A

1b fiber

77
Q

what are extrafusal muscle fibers

A

skeletal muscle fibers/cells that produce the contraction

78
Q

what motor neuron is in the extrafusal fibers and what does it do

A

alpha motor neuron- efferent neuron that releases Ach and causes contractino of the extrafusal fiber (skeletal muscle)

79
Q

what is the muscle spindle

A

small structure within the extrafusal fibers that contain intrafusal fibers that have sensory nerve endings wrapped around them that are sensitive to changes in muscle length

80
Q

what motor neurons are in the muscle spindle and what does it do

A

gamma motor neuron: efferent neuron that causes contraction of intrafusal fibers to mimic what the EF fibers are doing

81
Q

do jaw openers or jaw closers have a lot of muscle spindles

A

jaw closers

82
Q

what is the muscle spindle sensitive to

A

changes in muscle length

83
Q

what is the stimulus for the muscle spindle reflex

A

stretch

84
Q

what is the mechanism of action for muscle spindle reflex stimulus

A

-sensory fibers get squeezed in muscle spindle when stretched
- afferent information enters the spinal cord
- activates alpha motor neuron to stimulate extrafusal fiber contraction and inhibition of alpha motor neuron to antagonistic muscles
-activates the gamma motor neuron to stimulate intrafusal fiber contraction

85
Q

what would happen if intrafusal fibers did not contract

A

the sensory fibers would not be able to sense a further change in muscle length since there would be slack

86
Q

what is the effect of muscle spindle activation

A

contraction

87
Q

describe the muscle spindle reflex components

A

dynamic (immediate) and static (maintains tone- constant contraction)

88
Q

anytime the alpha motor neuron is activated what else is activated

A

the gamma motor neuron

89
Q

where are mechanosensitive receptors found at in golgi tendon organs

A

at the junction of tendons and muscle

90
Q

what are mechanoreceptors sensitive to in golgi tendon organs

A

changes in force

91
Q

what type of reflex is the golgi tendon organ reflex

A

protective

92
Q

what is the mechanism of action of the golgi tendon reflex

A

-extreme stretch of the tendon will squeeze the GTO and afferent neurons will send information into the spinal cord
- stimulates an inhibitory interneuron
- this neuron decreases the activity of the alpha motor neuron
-skeletal muscle contraction is decreased

93
Q

describe control of mastication

A

-mix of voluntary, reflex, and subconscious processes
- voluntary control is usually bilateral although people favor one side of the mouth over the other

94
Q

what is mastication controlled by

A

central pattern generator of the brainstem

95
Q

what are the neural components of mastication

A

CPG regulated by corticobulbar pathway

96
Q

where is the CPG located

A

in pons and medulla

97
Q

what nerve does the CPG use to send signals

A

trigeminal

98
Q

describe the jaw opening reflex

A

pain inhibits the alpha motor neuron of jaw closing muscles such as when you bite down on your tongue or spoon with incisors, jaw opens as a result

99
Q

describe the jaw jerk reflex

A

-strong tap to the chin stretches the jaw closers
-jaw closers respond by contraction so the jaw closes
-stretch reflex

100
Q

how do you determine the force needed to take a bite of something hard

A

-CPG starts chewing by activating jaw closing muscles
- the force of contraction is initally insufficient to overcome load (isometric)
- intrafusal fibers in muscle spindle are contracting and stretching the muscle spindle and signals further contraction of jaw closing muscles
-constant feedback from the muscle spindle in the jaw closing muscles is sufficient to overcome the load (isotonic)

101
Q

how do muscle spindles have protective action

A

-when nut cracks (for example) the force is now greater than the load
-there is more slack in muscle spindle now which leads to less activation of the muscle due to decreased alpha/gamma co-activation

102
Q

what distance separates the occlusal surfaces at rest

A

3-8 mm

103
Q

what happens to the jaw when you jog or run

A

force is applied to the mandible
- which each step there is a down movement of the mandible in relation to the head
- this movement stretches the muscle spindle which causes a reflex contraction of the jaw closing muscles

104
Q

what keeps the jaw in the rest position

A

muscle spindles

Physiology (41 decks)

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