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MED221A/B Lectures > MSK 15 - Skeletal muscle 2 > Flashcards

MSK 15 - Skeletal muscle 2 Flashcards

1
Q

what does skeletal muscle rely on to activate it

A

nerve AP travelling across the neuromuscular junction

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2
Q

what is the sequence of events that occur in the modulation of a muscle contraction - 3 steps

A

nerve AP travels across the neuromuscular junction

AP in nerve is sensed by muscle and gets a muscle AP

results in a twitch

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3
Q

in the modulation of a muscle contraction what is the time frame between the nerve AP and the muscle AP, what causes this

A

bit of a delay between the nerve AP and the muscle AP - this is because it takes time for neuromuscular transmission (a few milliseconds)

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4
Q

how long is the muscle AP and the muscle twitch

A

muscle AP = around 2-3milliseconds

muscle twitch is up to 200msec in duration

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5
Q

what are the conditions of the stimuli that creates unfused tetanus

A

stimuli far enough apart to allow for muscle relaxation slightly between stimuli

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6
Q

what are the conditions of the stimuli that creates summation

A

stimuli closer together such that they do not allow the muscle to relax fully before another stimuli causes another release of Ca2+ from the cytosol of that muscle fibre

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7
Q

what happens when muscle reaches a steady tension

A

summation has led to complete tetanus

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8
Q

if you continue stimuli at complete tetanus what happens over time

A

fatigue causes muscle to lose tension despite continuing stimuli

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9
Q

what do the Na+/Cl-/K+ channels across the sarcolemma do

A

balance ions across the membrane

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10
Q

what are the two things that the adrenaline receptor (B2 adrenoceptor) on the surface sarcolemma of a muscle cell can respond to

A

adrenaline or a B agonist

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11
Q

where are the adrenaline receptors found on the muscle cell

A

on the surface sarcolemma

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12
Q

what are the adrenaline receptors found on the muscle cell sarcolemma called

A

B2 adrenoceptor

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13
Q

when adrenaline or a B agonist binds to the B2 adrenoceptor what series of events happens and what is the end result

A

increased CAMP -> increased PKA -> react with DHPR and RyR1 and other targets like phospholamban (PLB)

overall it speeds up relaxation as phosphorylated PLB increases Ca2+ uptake by circa ATP-ase back into the SR and also increases force by increasing SR Ca2+ release via phosphorylation of RyR1

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14
Q

what is cAMP

A

cyclic AMP

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15
Q

what is PKA

A

protein kinase A

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16
Q

what is PLB

A

phospholamban

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17
Q

what does PLB do

A

controls/slows calcium ion uptake by SERCA (ATPase) back into SR

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18
Q

what is SERCA

A

sarcoplasmic reticulum Ca-ATPase

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19
Q

what happens when PLB is phosphorylated

A

speeds up the reuptake of Ca2+ into the SR = speeds up relaxation

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20
Q

what causes PLB to become phosphorylated

A

in response to B adrenergic reaction

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21
Q

increased B-adrenergic/adrenal activation will have what effect on force and contractions in fast twitch fibres

A

increase force and make it a faster and stronger contraction

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22
Q

does increased B-adrenergic/adrenal activation have the same effect on force and contractions in slow twitch fibres as they do in fast twitch fibres

A

no

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23
Q

increased adrenaline has what effect on skeletal muscle performance

A

increases performance

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24
Q

what is isometric contraction

A

contraction where no external shortening takes place so tension/force is developed but muscle length does not change

no movement generated

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25
what is the force of weight relative to force developed by muscles in isometric contraction
force of weight = force developed by muscles
26
what is internal shortening of a muscle
cross bridge cycling and sarcomere shortening
27
what are the two types of muscle contractions
isotonic and isometric
28
what is isotonic contraction
contraction where movement takes place and external shortening of muscle fibres occurs (muscle length changes)
29
what is the force of weight relative to force developed by muscles in isotonic contraction
produces more force than the objects weight mismatch between tension force generated by the contracting muscle and the constant load on the muscle
30
what are the two types of isotonic contraction
eccentric and concentric
31
what is concentric isotonic contractions
muscles shortens while generating force and overcomes resistance
32
what is an example of isotonic concentric contractions
Lifting a heavy weight, where the biceps contract to bend the arm at the elbow.
33
what is an example of isotonic eccentric contractions
Lowering a weight slowly during a bicep curl.
34
what is eccentric isotonic contractions
Muscles elongate/lengthen while still generating force.
35
what is eccentric isotonic contractions in terms of the forces generated
Eccentric contractions occur when the opposing force (resistance) is greater than the force generated by the muscle. force of weight > force developed by muscles
36
what is the common form of muscle contraction that damages skeletal muscle
eccentric isotonic contractions
37
what is concentric isotonic contractions in terms of forces
force of weight < force developed by muscles
38
what condition is associated with eccentric contractions
delayed onset muscle soreness
39
can skeletal muscle heal and why is this
yes skeletal muscle have satellite cells around its muscle fibres so when there's damage myoblasts can be assembled and repair fibres
40
what can be aided by eccentric contractions why is this
muscle growth as a result of the eccentric muscle damage causing release of cytokines
41
what happens to the force when sarcomeres are stretched beyond their optimal length
the force developed is alot less
42
what is the popping sarcomere theory
weakest sarcomeres in series will always lengthen first giving rise to the popping sarcomere
43
what is the combination of conditions that causes DOMS
muscle and connective tissue microtrauma followed by inflammatory processes and oedema
44
is the lactic acid theory still supported and why is this
lactic acid theory has been rejected concentric contractions that produces lactic acid does not cause DOMS, lactic acid also returns to normal levels within one hour of exercise so therefore cannot cause the pain that occurs hours afterward
45
what kind of force increases with increased length
passive force
46
at what length do skeletal muscles generate the greatest force
at their resting/ideal length
47
when muscles are shortened or elongated what happens to the force they generate and why is this
force decreases for stretched muscles it is because you increased the passive force of the muscle
48
explain in terms of the sarcomeres myosin and actin filament arrangements why lengthening the muscle beyond optimal length will decrease the force generated
very few cross bridges can form between actin and myosin as there is less overlap so force generated decreases
49
the force that muscles generate is directly proportional to what factor
to the number of cross bridges that can form - ie the number of myosin that can bind to actin binding site to develop force
50
explain in terms of the sarcomeres myosin and actin filament arrangements why shortening the muscle beyond optimal length will decrease the force generated
sarcomeres will buckle and twist at short lengths and lose their orientations causes interference with actin filaments that blocks cross bridges from forming (some cross bridges might be working in the opposite direction because of sarcomere shortening)
51
what is the passive force
force on muscle depending on length you have isolated muscle at
52
what is the preload
the load experienced by the muscle in a relaxed state (muscle length) putting force on muscle and muscle adjusts to this set length (sets sarcomere length)
53
what is the afterload
load a muscle works against during contraction
54
what contractions are involved to lift afterload
isotonic contractions
55
what is the total load
load experienced by the muscle during contraction its the sum of preload plus afterload
56
as the load opposing contraction is increasing then the velocity of the shortening should ___ why is this
decrease external shortening of muscle during isotonic contraction is going to be decreased if you shortening against a heavier load
57
in isotonic contractions what is the relationship between load on muscle and speed of shortening
if the load on the muscle is constant then the speed of shortening should be constant
58
isometric contraction occurs when maximum force developed by cross bridges is balanced with what
balanced with the load
59
what happens if in isometric contraction even more force is applied to the muscle beyond the maximal force developed by the cross bridges (ie if afterload is too heavy)
then the muscle will stretch leading to eccentric contraction - negative shortening
60
what is the SI unit for force
Newtons (kgms^-2)
61
what is the SI unit for work
Joule
62
what is the SI unit for power
Watt
63
what is the most important property of muscle that limits maximum sprinting speed
force velocity relationship
64
power of a muscle depends on what
depends on the rate of muscle shortening
65
is power generated in isometric contraction - why or why not
no because there is no movement generated in isometric contractions meaning that though you are developing force there is no work done and therefore no power
66
where is the maximum power generated in skeletal muscle (ie contractions are most efficient at what length of shortening)
at around 1/3 of maximum load that you can put on a muscle for it to be producing isotonic concentric contraction around 1/3 of the max rate of shortening
67
in order to sustain contractile activity what must skeletal muscle do in terms of muscle metabolism
must produce molecules of ATP as rapidly as their breakdown
68
what the 3 sources of ATP
creatine phosphate oxidative phosphorylation glycolysis
69
where does creatine phosphate target for ATP production
targets phosphate delivery to where ATP is consumed
70
does lactic acid exist in skeletal muscle - explain why
no lactic acid is transported to plasma and is converted to lactate and protons
71
what timeframe can glycolysis supply skeletal muscles with ATP
short term energy supply around 1-2mins
72
what timeframe can ATP-CP supply skeletal muscles with ATP
immediate energy supply depletes quite rapidly
73
what timeframe can aerobic respiration supply skeletal muscles with ATP
long term energy supply for system
74
how many isoforms does actin have
2
75
how many isoforms does tropomyosin have
2
76
how many isoforms does myosin have
at least 7
77
what is the differences in sarcomere filament isoforms
some isoforms have different rates of which they need energy
78
do muscles only have fast/slow fibres or a mix of both
a mix of both depending on function
79
what are the 2 types of skeletal muscle fibre types
type IIB = fast glycolytic type I = slow oxidative
80
what kinds of muscles does Type 1 fibres tend to be
postural muscles
81
what are 3 possible causes of muscle weakness
muscle fatigue muscular dystrophy sarcopenia
82
what is the definiton of muscle fatigue
failure to maintain the required/expected power output leading to reduced muscle performance
83
what is the possible theory of why muscle fatigue happens
accumulation of metabolites depletion of muscle energy supplies such as glycogen
84
what are the 2 types of muscle fatigue
central and peripheral fatigue
85
what is central fatigue in terms of what causes it
decreased activation from CNS = decreased number of motor units recruited
86
what is peripheral fatigue in terms of what they affect
affecting the cellular mechanisms that control force such as smaller Ca2+ transient, reduced Ca2+ sensitivity of myofilaments and slower cross bridge cycling
87
does muscle fatigue occur in fast twitch fibres, slow twitch fibres or both
mostly in fast twitch fibres slow twitch fibres are much more fatigue resistant than fast twitch muscles
88
describe T tubular K+ 's role in the metabolite accumulation theory of fatigue
decreases membrane excitability everytime you have an AP the K+ conc increases outside builds up in T tubule so that the membrane is depolarised partially such that it is less excitable
89
describe NH4+'s role in the metabolite accumulation theory of fatigue
decreases membrane polarity and excitability and also inhibits myosin ATPase
90
describe Pi's role in the metabolite accumulation theory of fatigue
build up of inorganic phosphate within SR causes precipitate that inhibits Ca2+ release, decreases Ca2+ uptake, decreases myofilament Ca2+ sensitivity and inhibits the power stroke
91
describe reactive oxidative species' role in the metabolite accumulation theory of fatigue
increases protein damage
92
what are the clinical features of Duchennes muscular dystrophy
muscles normal at birth but increasing skeletal muscle weakness and degeneration
93
what is Duchennes muscular dystrophy caused by
mutation in dystrophin gene which causes loss of dystrophin
94
what is the early stages of Duchennes muscular dystrophy characterised by give examples of what can happen due to this
increased cell membrane permeability such that soluble enzymes like creatine kinase leak out and ions like Ca2+ enter
95
what does dystrophin do within muscle cells
link to contractile proteins with sarcolemma in some way so that force developed by contractile proteins during cross bridge cycling can be transmitted across the cell membrane
96
what is sarcopenia mainly caused by
aging
97
what happens in sarcopenia to the muscle and what does this mean in terms of strength
muscle mass/body mass ratio decreased significant loss of muscle strength
98
in terms of nerves and fibres what happens in sarcopenia
denervation of fast fatigable fibres and motor units and motor unit remodelling
99
in sarcopenia there is a ____ in the capillary:fire ratio
decrease

MED221A/B Lectures (23 decks)

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