Skeletal muscle Flashcards
(93 cards)
1
Q
what are the three types of muscle
A
skeletal
cardiac
smooth
2
Q
smooth muscle
A
involuntary, found in hollow organs
3
Q
what is the latent state of smooth muscle
A
when the muscles stay contracted for longer periods of time
4
Q
cardiac muscle
A
involuntary, found in the heart
5
Q
skeletal muscle
A
voluntary, moves the skeleton
has the greatest level of organization
6
Q
anatomy of skeletal musle
A
- muscle body/entire muslces
- fasciculi
- muscle fibers
- myofibrils
- sarcomere
7
Q
what is the muscle body and what is it surrounded by
A
the entire muscle surrounded by the epimysium
8
Q
what are the fasciculi and what is surrounded by
A
smaller bundles of muscle fibers that make up the entire muscle
- surrounded by perimysium
9
Q
what are muscle fibers and what are they surrounded by
A
smaller bundles of myofibrils that make of the fascicles
- surrounded by endomysium
10
Q
myofibrils
A
strainds of protein that bundle up to form muscle fibers
- contains the sarcomere
11
Q
sarcomere
A
the basic contractile unit of a muslce fiber
- contains myosin heavy chain and actin proteins
- titin: the largest protein in the body holds myosin in place
12
Q
mysoin heavy chain characteristics
A
- darker under the microscope
- two intertwined filaments with globular heads
- heads have ATPase
13
Q
what part of the sarcomere contains MHC
A
A band (both actin and myosin) and H zone
14
Q
actin filament characteristics
A
- shows up lighter under a microscope w/ 3 proteins
- contains myosin binding sites
- wrapped with a tropomyosin that covers the binding sites at rest
- troponin complex is anchored to actin and moves tropomyosin when Ca2+ binds
15
Q
what are the parts of muscle fibers
A
- plasmalemma
- satellite cells
- sarcoplasm
- transverse tubules (T-tubules)
- sarcoplasmic reticulum
16
Q
plasmalemma
A
- the cell membrane of the muscle cells
- conducts action potentials, maintains pH, transports neurtrients
- fuses with tendon
17
Q
satellite cells
A
- allows for muscle growth and development
- muscle cells share DNA with satellite cells
18
Q
what is the role of satellite cells
A
- helps to respond to injury, immobilization effects and training
- more DNA shared with satellite cells makes recovery faster, can get back to normal after longer periods of rest fasters
19
Q
sarcoplasm
A
the cytoplasm of the muscle cell
- helps to store glycogen and myoglobin
20
Q
when is greater glycogen storage seen
A
with resistance training
21
Q
when is greater myoglobin storage seen
A
with aerobic exercise
22
Q
transverse tubules
A
extensions of plasmalemma that carries AP deeper into muscle cells
23
Q
sarcoplasmic reticulum
A
- lattice structure that surrounds the muscle cells
- storage for Ca2+
24
Q
what is the most important molecule in muscle physiology
A
Ca2+
25
how many muscle fibers are humans born with vs when they die, why?
- the same amount of muscle fibers from birth to death
- humans experience hypertrophy instead of hyperplasiahy
26
hypertrophy
the increase in muscle size
27
hyperplasia
the increase in number of muscle cells
- seen in cats
28
motor units
single alpha motor neuron and all the fibers it innervates
29
fine motor units
less muscle fibers are innervated to produce more precise movements
30
gross motor unit
more muscle fibers are innervated allows for compound or larger movements
31
neuromuscular junction
site of communication between neuron + muslce cell
32
what are the mechanism that allows for a muscle contraction to occur
exititation-contraction coupling
33
excitation steps of the excitation-contraction coupling mechansism
1. AP starts in the brain traveling down the spinal cord
2. AP arrives at the neruon travelling through axon reaching axon terminal = voltage gated calcium ion channels open
3. Ca2+ enters the axon terminal = signals release of ACh release from synaptic vesicles
4. ACh crosses synapse into neuromuscular junction + binds to ACh receptors on plasmalemma
5. Na+ channels open = localized depolarization & depoloarizing end plate potential
6. initiate wave of AP through sarcolemma and goes down through T tubules
7. charge in T tubules turns on dihydropyridine receptors activating ryanodine receptors = mass release of Ca2+ into the sarcoplasm
34
how is the SR sensitive to changes in electrical charge
due to voltage triggering that turns on the dihydropyridine receptors
35
contraction steps of excitation-contraction coupling
1. Ca2+ release from SR increases concentration in the sarcoplasm
2. Ca2+ binds to troponin = pulls tropomyosin off myosin binding sites (exposed now)
3. myosin binds on the mysoin binding site on the actin = crossbridge formation
36
how is localized depolorization regualted
acetylcholinesterase
37
acetylcholinesterase
enzyme that breaks down ACh in the neuromuscular junction
- occurs immediately to make sure it stops
38
what would happen if acetylcholinesterase was absent
would cause prolonged muscle contractions
39
what does ACh do in different locations
- muscles = stimulation of muscle contractions
- cardiac muscle = could suppress HR
- nose = increase in mucous production
40
sliding filament theory
the actually process of actin-myosin contraction
41
sliding filament theory steps
- in relaxed state theres no actin myosin contraction
- contracted state the myosin head pulls actin towards sarcomere center (sliding past each other)
- sarcomere shortens during contraction
- after Powerstroke occurs myosin detaches are attaches further down
42
with the sliding filament theory when does the process continue until
- until myosin reaches zdisk
- AP stops and Ca2+ is pumped back into the SR
43
what is the energy for muscle contraction and how does it affect contraction
- ATP
- ATP binds to myosin head = release of myosin + actin binding
- ATP is hydrolized into ADP and Pi due to the ATPase
- new ATP allows for release of hydrolyzed ATP to be released and for a crossbridge to release
44
what happens if ATP is absent
in a state of rigor or constant contraction
45
what happens within the muscle cell during muscle relaxation
- AP ends and electrical stimulation of SR stops
- Ca2+ pumped back into SR to be stored until next AP arrives
- shuttling back uses ATP known as SERCA
- tropomyosin returns back to covering mysoin binding
46
SERCA
sarcoplasmic/endoplasmic reticulum Ca2+ ATPase
47
what are the types of biomechanical properties of muscle fiber types?
- oxidative capacity: different # of capillaries
- type of myosin ATPase: the speed of degradation (type I or type II)
48
what are contractile properties
maximal force production
speed of contraction
muscle fiber efficiency
49
what does speed of contraction depend on
mysosin ATPase activity
50
what are the types of muscle fibers
Type I
Type IIa
Type IIx/IIb
51
Type I muscle fiber
- aerobic (oxidative)
- approx 50% of fibers in an average muscle
- more mitochondria, more capillaries
- peak tension in 110 ms (slow twitch, slow contractile speed)
- high oxidative capacity
- low glycolytic capacity
- high fatigue resistance
- low motor unit strength
52
Type II muscle fibers
- peak tension in 50 ms (fast twitch)
- good sugar metabolism
- has more enzymes for glycolysis
53
Type IIa muscle fiber type
- intermediate fibers, fast-oxidative glycolytic
- moderately high oxidative capacity
- high glycolytic capacity
- fast contractile speed
- moderate fatigue resistance
- high motor unit strength
54
Type IIb muscle fiber type
- fast twitch, fast glycolitic
- low oxidative capacity
- highest glycolytic capacity
- fast contractile speed
- low fatigue resistance
- high motor unit strength
55
how does the size of motor unit affect activation
- smaller motor units are easier to activate compared to larger ones
- Type I: smaller
- Type IIa: larger
- Type IIb: larger
56
how does muscle fiber shift occru
- slow process
- can increase mitochondria, capillaries, glycogen storage, etc.
57
what muscle fiber type has the greatest peak power
Type IIx
- due to effects of different SR, motor units, etc.
58
when do muscle fibers reach peak power
at approx 20% peak force for all muscle fiber types
59
how are muscle fiber types distributed among individuals
roughly 50/50 but can change depending on training
60
how do arm and leg ratios of muscle fibers compare
endurance athletes = predominantly Type I
power athletes = predominantly type II
61
what is the muscle that is type I in everyone
soleous bc it helps to reduce the affects of gravity
62
what is the muscle fiber type composition of the extensor digitorum longus
predominantly type II
63
what are the two methods of typing a muscle fiber
muscle biopsys and staining
64
what is the issue with muscle biopsies in determining muscle fiber type
not representative of the whole body
65
what are the different stainings of muscle fibers
- Type I: appears the darkets
- Type IIa: lightest
- Type IIb: in between
66
myoplasticity
the quantiative and qualitative changes in muscle
66
quantitative changes in muscles
amount of myoglobin or number of enzymes
67
Type I muscle fibers during exercise
- used in high aerobic endurance activities or daily activities
- requires oxygen for ATP production (gets from fat + carbs)
- takes hours to fatigue but also can be different based on lifestyle (e.g. sedentary)
68
qualitative changes in muscles
change in type via actin and myosin or type of SERCA pumps
69
Type II muscle fibers during exercise
- poor aerobic endurance
- fatigue quickly and produce ATP anaerobically
- limited by the amount of sugar in the body (but can be replenished post exercise from sugar stores into the bloodstream)
70
is muscle pain always a result of lactic acid build up
no
- sometimes due to the inabilty of pyruvate to convert to lactate which decreases pH in muscle = pain
71
what can be done to deal with muscle pain during exercise
- bicarb loading to help use as a buffer in the muscles
- this is dangerous though as it can cause GI issues if done in excess
72
Type IIa muscle fibers during exercise
- more force and faster fatigue than in type I
- short and high intensity endurance events (eg 1600m run)
73
Type IIb muscle fibers during exercise
- seldom used for everday activities (emergency movements if anything)
- short explosive sprints, exercises against a load
- once activity is done will immediately stop
- relies heavily on sugar metabolism as it has no mitochondria
74
what are some factors that determine fiber type within a body
- genetic factors
- training factors
- aging
75
how do genetics determine fiber type
- myocytes need to be told what they are so they differentiate based on motor neuron
- alpha motor neuron will innervate certain fibers
76
how do training factors affect fiber type determination
- endurance vs. strength training and detraining (trained individuals can recover faster)
- training can induce small 10% changes in fiber types
- untrained individuals can see up to a 20% change than in trained individual
77
which muscle sees changes faster during training
the antagonist muscle before the main muscle
78
what determines success in training
muscle type, cardiovascular function, motivation, training habits, muscle size
79
how does aging affect muscle type
with age people lose type II motor units (which is strength)
- this is why people have harder times performing ADLs as they age
80
how does endurance training affect skeletal muscle adaptations
produced cellular adaptations: higher oxidative capacity, faster removal of waste, increased angiogenisis, increased myoglobin
81
how does endurance affect muscle fiber type transitions
endurance shifts from type IIx to type IIa and with further training type I
82
when is initial atrophy seen
within two days due to decreased protein synthesis
83
how much muscle mass is lost betwee ages 25-50 yrs
20%h
84
how much muscle mass is lost between 50-80 yrs
an additional 40%
85
what is the orderly recruitment principle
recruit minimun number of motor units needed then slowly increase based on activity
- same order each time (type I --> type II a --> type IIb)
86
what is the size principle
order of recruitment of motor units directlu related to size of alpha motor neuron
87
what is the relationship between firing rate and recruitment threshold for type I fibers
Type I muscle fibers have high mean firing rate and a low recruitment threshold
88
parts of a muscle twitch
- stimulus: the initiation of a conraction
- latent period: the period post stimulus where nothing occurs (approx 5 ms)
- contraction: tension is developed ( 40 ms)
- relaxation (50 ms)
89
how of shortening related to the muscle fibers
faster speeds of contractions are seen in faster fibers bc the SR releases Ca2+ at a faster rate and higher ATPase activity
90
what does force regulation of muscle action depend on
- the type of motor unite used: the use of more motor units = greater force or the use of fast motor units = greater force
- initial muscle length: too long or too short will not produce enough
- frequency of stimulation: simple twitch, summation, tetanus
91
summation
- increase in simple twitches that result in the sum of them with increases forceta
92
tetanus
sustained muscle contraction when stimulus occurs at high frequency (max force generated
