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MSS - MSK Exam 3 > Skeletal Muscle Physiology > Flashcards

Skeletal Muscle Physiology Flashcards

1
Q

muscle twitch

A

mechanical response to action potential

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2
Q

latent period

A

from AP initiation to cross bridge formation

-start of contraction

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3
Q

contraction time

A

beginning of contraction to beginning of relaxation
-until peak tension

active sites exposed to when they begin to be covered up

when Ca2+ is high enough to keep active sites exposed

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4
Q

relaxation time

A

peak tension to complete relaxation

Ca2+ sequestering into the SR

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5
Q

total force generated?

A

tension
sum of forces independently produced by many cycling cross-bridges

can vary with:
initial length of muscle fiber
pattern or frequency of muscle fiber stimulation

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6
Q

isometric contraction

A

muscle length constant
increase in tension, but no shortening

force production is equal to resistance

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7
Q

isotonic contraction

A

contraction occurs at constant load
-not really a constant force

length change occur

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8
Q

two phases of isotonic contraction

A

concentric and eccentric

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9
Q

concentric phase

A

muscle shortens as tension is produced

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10
Q

eccentric phase

A

muscle lengthens as tension is produced

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11
Q

length-tension relationship

A

for isometric contractions
-force production depends on initial fiber length

muscle length influences tension devleopment by determining region of overlap between actin and myosin

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12
Q

passive tension

A

tension prior to muscle contraction

increases as fiber is progressively lengthened because muscle becomes stiffer as it is distended

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13
Q

active tension

A

total tension - passive tension

cuased when cross-bridge cycling occurs in isometric contraction (fixed length)

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14
Q

when is active tension maximal?

A

near 100% of normal muscle length

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15
Q

what happens with increased fiber length?

A

ends of actin are pulled away from each other

greater than 150% - ends of actin are pulled beyond myosin

no interaction/overlaps occur and therefore no development of tension

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16
Q

what happens with decreased fiber length?

A

actin and myosin increase overlap
ends of actin filaments are pushed toward eachother

-tension can develop depending on degree of overlap

shortening to less than 70-85% of resting length
-opposing actin filaments slide over one another and hit Z disks

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17
Q

normal resting length?

A

of sarcomere

maximal overlap between actin and myosin filaments and maximal active tension

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18
Q

total tension = ?

A

passive + active tension

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19
Q

force-velocity relationship

A

in isotonic contractions

shortening velocity decreases as load increases

**lighter loads can be lifted faster

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20
Q

maximum velocity?

A

determined primarily by maximum velocity of myosin ATPase enzyme

Vmax also varies with fiber type

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21
Q

smaller the load?

A

greater the shortening velocity

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22
Q

larger the load?

A

the lower the shortening velocity

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23
Q

what is contraction at zero velocity?

A

ISOMETRIC!

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24
Q

at a given fiber length?

A

there is a hyperbolic relationship between shortening velocity and load

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25
Q

what does maximal velocity depend on?

A

maximal rate of cross-bridge turnover
-not on initial overlap of thin and thick filaments

therefore, it is independent of length

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26
Q

longer the initial fiber length?

A

the larger the maximal load under zero-velocity conditions

aka isometric conditions

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27
Q

work = ?

A

load x displacement

measureable mechanical work
-only when muscle displaces a load

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28
Q

power = ?

A

work/time

maximal at intermediate lads
-where both F and v are moderate

zero load F= 0
maximum load v = 0

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29
Q

power also = ?

A

load x displacement / time

aka load x velocity (Fv)

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30
Q

frequency summation?

A

tension of single fiber can be summed if APs fire rapidly

aka twitch summation

repetitive stimulation leads to increased tension

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31
Q

what causes frequency summation?

A

no fiber relaxation between stimuli due to sustained levels of Ca2+

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32
Q

tetanus?

A

twitches merge to a smooth, sustained, maximal contraction

result of high stimulation frequency
-muscle tension at a plateau

Calcium levels are sustained until tetanic stimuli ceases

tension increases very little at stimulation frequencies greater than the fusion frequency that causes tetanus

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33
Q

fusion frequency?

A

frequency of signals that lead to tetanus

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34
Q

motor unit?

A

single motor neuron and the muscle it innervates

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35
Q

whole muscle tension depends on?

A

size of muscle
number of motor units recruited
size of each motor unit recruited

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36
Q

muscles for refined, delicate movements?

A

few muscle fibers per motor unit

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37
Q

muscles performing stronger, coarser movements?

A

large number of fibers per motor unit

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38
Q

MMUS?

A

multiple motor unit summation

in skeletal muscle - increased force production with summation of multiple fibers

CNS can control how many individual fibers it stimulates

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39
Q

motor neuron pool

A

group of all motor neurons innervating a single muscle

40
Q

asynchronous recruitment

A

some units develop tension while others relax

delays and prevents muscle fatigue during SUBMAXIMAL contraction

41
Q

contractile strength can vary with?

A

number of active alpha-motor neurons in pool

frequency of firing of each alpha motor neuron

42
Q

EMG

A

gross measure of electrical activity

43
Q

hennemans size principle

A

size of cell body dictates excitability
smaller are more excitable
-threshold reached sooner

small recruited first, followed by larger

44
Q

given excitatory stimulus…

A

will generate a larger EPSP in motor neurons with smaller cell bodies

45
Q

slow-twitch motor unit

A

I

small amount of force, prolonged period of time

46
Q

fast-twitch fatigue-resistant motor unit

A

FR

moderate amount of force, sustained for moderate amount of time

47
Q

fast-twitch fatigable motor unit

A

FF

larger amount of force, brief period of time

48
Q

order of recruitment of motor units?

A

I > FR > FF

49
Q

type I motor units?

A

small cell diameter
fast conduction
high excitability

50
Q

type II motor units?

A

large cell diameter
very fast conduction
low excitability

51
Q

muscle fatigue

A

inability to maintain desired power output

decline in force production and shortening velocity

decline in maximal force production - from decreased number of active cross bridges

lower rates of force production and relaxation
-bc of impaired release and uptake of calcium from SR

52
Q

role of fatigue?

A

protective

-allows contraction to occur at lower rates/forces while preventing extreme changes that can damage

53
Q

muscle fatigue reversible?

A

yes, with rest

versus damage or weakness which compromise ability to develop force

54
Q

factors contributing to fatigue

A

motivation, physical fitness, nutrition, type of motor unit recruited

55
Q

central fatigue

A

changes in CNS
-brain > motor neuron cell bodies

can be opposed by cheering
-seriously though.

56
Q

peripheral fatigue

A

motor neuron axon > NMJ > fiber

impaired APs, Ca release, depletion of metabolism substrates, accumulation of byproducts

57
Q

peripheral fatigue and time required for recover depend on?

A

recruitment pattern and fiber type

58
Q

anaerobic sources of ATP?

A 
creatine phosphate (fast)
glycolysis (pretty fast)
59
Q

aerobic source of ATP?

A

oxidative phosphorylation (slow)

60
Q

slow twitch muscles?

A

type I

61
Q

fast twitch muscles?

A

type II

62
Q

different fiber types how?

A

different myosin heavy chain isoforms

-difference in mATPase activity corresponds to rate of contraction

can be hybrid fibers with intermediate rates

63
Q

type I fibers?

A

slow oxidative fibers

64
Q

type IIA fibers?

A

fast-oxidative fibers

65
Q

tyoe IIX fibers?

A

fast-glycolytic fibers

66
Q

how are skeletal muscle fiber types classified?

A

pathway for ATP synthesis (ox vs. glycolytic)
rate of ATP hydrolysis (mATPase isoform)
contractile velocity (fast vs. slow)

67
Q

slow-twitch fibers?

A 
smaller cross section
greater oxygen transport ability
more capillaries
appear red (myoglobin)
low glycogen
high mitochondria
resistant to fatigue
68
Q

type IIA fiber characteristics?

A 
fatigue resistant
oxidative metabolism
-red (myoglobin)
-mitochondria high
-abundant glycogen**
more capillaries

ensures adequate ATP generation for rapid depletion with rapid contraction

69
Q

type IIX fiber characteristics?

A 
fatigable
rely on glycolysis
few mitochondria
white (low myoglobin)
high glycolytic enzyme content
high glycogen
70
Q

slow-twitch fibers?

A

tetanize at lower stimulation frequencies

71
Q

fast-twitch fibers?

A

develop larger maximal force due to greater twitch tesion and larger motor units

72
Q

proprioception

A

detailed information sensed about location in space, direction, and speed of movement

73
Q

2 main purposes of proprioception?

A

identify external objects

accurately guide movement

74
Q

muscle proprioception?

A

afferent info to regulate skeletal muscle activity

75
Q

muscle spindles

A

detect changes in muscle length and rate of stretch

76
Q

golgi tendon organs

A

detect muscle tension in muscle tendon

77
Q

muscle spindle structure?

A

intrafusal muscle fibers aligned in parallel with force generating extrafusal fibers

78
Q

golgi tendon structure?

A

aligned in series with extrafusal fibers

79
Q

function of muscle spindle

A

send proprioceptive info about muscle to CNS

respond to muscle stretch

80
Q

two kinds of intrafusal fibers?

A

bag and chain

81
Q

two kinds of sensory endings

A

primary and secondary

82
Q

primary sensory endings?

A

of group Ia axons
innervate bag fibers (in addition to chain fibers)

sensitive to change in length

83
Q

secondary sensory endings?

A

of group II axons
innervate mainly chain fibers

transduce static length
-slowly adapting receptors

84
Q

what happens when muscle stretches?

A

firing rate of sensory fibers increased

85
Q

gamma motor neuron

A

to contractile region of spindle fiber

86
Q

alpha motor neuron

A

output to regular skeletal muscle fiber

87
Q

stretch reflex pathway?

A

afferent from muscle spindle

alpha to skeletal muscle

88
Q

why does muscle spindle also have motor innervation?

A

alpha motor contract extrafusal fiber and the spindle becomes slackened

gamma not neurons help to maintain the sensitivity of the spindle apparatus

89
Q

sensory response of spindle depends on what?

A

length of whole muscle AND contractile state of intrafusal fiber

90
Q

reflex

A

basic neural function, involves simple neural circuits

91
Q

motor reflex

A

rapid, stereotyped motor response to a particular sensory stimulus

motor neurons receive many synaptic inputs within the brain and spinal cord

92
Q

stretch reflex

A

type of monosynaptic reflex
-myotatic

group Ia sensory axons terminate monosynaptically on alpha motor neurons innervating same muscle

93
Q

reciprocal innervation

A

as stretched muscle contracts, parallel circuits inhibit the alpha motor neurons of the antagonist

Ia sensory axons stimulate inhibitory interneurons that synapse with alpha motor neurons of antagonist

94
Q

golgi tendon organs

A

autogenic inhibition
-protective refelx

group Ib axons in encapsulated collagen matrix

located at musculotendinous junction

increased muscle tension

located at musculotendinous junction

GTOs may respond to passive stretch, but especially respond during active muscle contractions

95
Q

group Ib sensory axons?

A

in golgi tendon organs

96
Q

autogenic inhibition

A

GTO circuit inhibits the muscle in which tension increased and excites the antagonist

response usually opposite the stretch reflex

in general, GTO mediated reflexes act to control muscle force and joint stability

MSS - MSK Exam 3 (16 decks)

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