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MSS - MSK Exam 3 > Skeletal Muscle Physiology > Flashcards

Skeletal Muscle Physiology Flashcards

(96 cards)

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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
what does maximal velocity depend on?
maximal rate of cross-bridge turnover -not on initial overlap of thin and thick filaments therefore, it is independent of length
26
longer the initial fiber length?
the larger the maximal load under zero-velocity conditions aka isometric conditions
27
work = ?
load x displacement measureable mechanical work -only when muscle displaces a load
28
power = ?
work/time maximal at intermediate lads -where both F and v are moderate zero load F= 0 maximum load v = 0
29
power also = ?
load x displacement / time aka load x velocity (Fv)
30
frequency summation?
tension of single fiber can be summed if APs fire rapidly aka twitch summation repetitive stimulation leads to increased tension
31
what causes frequency summation?
no fiber relaxation between stimuli due to sustained levels of Ca2+
32
tetanus?
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
33
fusion frequency?
frequency of signals that lead to tetanus
34
motor unit?
single motor neuron and the muscle it innervates
35
whole muscle tension depends on?
size of muscle number of motor units recruited size of each motor unit recruited
36
muscles for refined, delicate movements?
few muscle fibers per motor unit
37
muscles performing stronger, coarser movements?
large number of fibers per motor unit
38
MMUS?
multiple motor unit summation in skeletal muscle - increased force production with summation of multiple fibers CNS can control how many individual fibers it stimulates
39
motor neuron pool
group of all motor neurons innervating a single muscle
40
asynchronous recruitment
some units develop tension while others relax delays and prevents muscle fatigue during SUBMAXIMAL contraction
41
contractile strength can vary with?
number of active alpha-motor neurons in pool | frequency of firing of each alpha motor neuron
42
EMG
gross measure of electrical activity
43
hennemans size principle
size of cell body dictates excitability smaller are more excitable -threshold reached sooner small recruited first, followed by larger
44
given excitatory stimulus...
will generate a larger EPSP in motor neurons with smaller cell bodies
45
slow-twitch motor unit
I | small amount of force, prolonged period of time
46
fast-twitch fatigue-resistant motor unit
FR | moderate amount of force, sustained for moderate amount of time
47
fast-twitch fatigable motor unit
FF | larger amount of force, brief period of time
48
order of recruitment of motor units?
I > FR > FF
49
type I motor units?
small cell diameter fast conduction high excitability
50
type II motor units?
large cell diameter very fast conduction low excitability
51
muscle fatigue
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
role of fatigue?
protective | -allows contraction to occur at lower rates/forces while preventing extreme changes that can damage
53
muscle fatigue reversible?
yes, with rest versus damage or weakness which compromise ability to develop force
54
factors contributing to fatigue
motivation, physical fitness, nutrition, type of motor unit recruited
55
central fatigue
changes in CNS -brain > motor neuron cell bodies can be opposed by cheering -seriously though.
56
peripheral fatigue
motor neuron axon > NMJ > fiber impaired APs, Ca release, depletion of metabolism substrates, accumulation of byproducts
57
peripheral fatigue and time required for recover depend on?
recruitment pattern and fiber type
58
anaerobic sources of ATP?
``` creatine phosphate (fast) glycolysis (pretty fast) ```
59
aerobic source of ATP?
oxidative phosphorylation (slow)
60
slow twitch muscles?
type I
61
fast twitch muscles?
type II
62
different fiber types how?
different myosin heavy chain isoforms -difference in mATPase activity corresponds to rate of contraction can be hybrid fibers with intermediate rates
63
type I fibers?
slow oxidative fibers
64
type IIA fibers?
fast-oxidative fibers
65
tyoe IIX fibers?
fast-glycolytic fibers
66
how are skeletal muscle fiber types classified?
pathway for ATP synthesis (ox vs. glycolytic) rate of ATP hydrolysis (mATPase isoform) contractile velocity (fast vs. slow)
67
slow-twitch fibers?
``` smaller cross section greater oxygen transport ability more capillaries appear red (myoglobin) low glycogen high mitochondria resistant to fatigue ```
68
type IIA fiber characteristics?
``` fatigue resistant oxidative metabolism -red (myoglobin) -mitochondria high -abundant glycogen** more capillaries ``` ensures adequate ATP generation for rapid depletion with rapid contraction
69
type IIX fiber characteristics?
``` fatigable rely on glycolysis few mitochondria white (low myoglobin) high glycolytic enzyme content high glycogen ```
70
slow-twitch fibers?
tetanize at lower stimulation frequencies
71
fast-twitch fibers?
develop larger maximal force due to greater twitch tesion and larger motor units
72
proprioception
detailed information sensed about location in space, direction, and speed of movement
73
2 main purposes of proprioception?
identify external objects | accurately guide movement
74
muscle proprioception?
afferent info to regulate skeletal muscle activity
75
muscle spindles
detect changes in muscle length and rate of stretch
76
golgi tendon organs
detect muscle tension in muscle tendon
77
muscle spindle structure?
intrafusal muscle fibers aligned in parallel with force generating extrafusal fibers
78
golgi tendon structure?
aligned in series with extrafusal fibers
79
function of muscle spindle
send proprioceptive info about muscle to CNS | respond to muscle stretch
80
two kinds of intrafusal fibers?
bag and chain
81
two kinds of sensory endings
primary and secondary
82
primary sensory endings?
of group Ia axons innervate bag fibers (in addition to chain fibers) sensitive to change in length
83
secondary sensory endings?
of group II axons innervate mainly chain fibers transduce static length -slowly adapting receptors
84
what happens when muscle stretches?
firing rate of sensory fibers increased
85
gamma motor neuron
to contractile region of spindle fiber
86
alpha motor neuron
output to regular skeletal muscle fiber
87
stretch reflex pathway?
afferent from muscle spindle | alpha to skeletal muscle
88
why does muscle spindle also have motor innervation?
alpha motor contract extrafusal fiber and the spindle becomes slackened gamma not neurons help to maintain the sensitivity of the spindle apparatus
89
sensory response of spindle depends on what?
length of whole muscle AND contractile state of intrafusal fiber
90
reflex
basic neural function, involves simple neural circuits
91
motor reflex
rapid, stereotyped motor response to a particular sensory stimulus motor neurons receive many synaptic inputs within the brain and spinal cord
92
stretch reflex
type of monosynaptic reflex -myotatic group Ia sensory axons terminate monosynaptically on alpha motor neurons innervating same muscle
93
reciprocal innervation
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
golgi tendon organs
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
group Ib sensory axons?
in golgi tendon organs
96
autogenic inhibition
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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