Skeletal Muscle - Force, Work, and Energy Flashcards
1
Q
How do muscles enhance their peak tension?
A
Muscles can enhance their peak tension production by BEING LARGER
High peak tension = creates more power
However, larger muscles have their drawbacks:
- use more energy (even at rest)
- ADD WEIGHT (VERY HEAVY)
- take up room/space
2
Q
Which one would produce more tension?
A muscle with some motor units active or all motor units active?
A muscle with more fibres per fascicle or fewer fibres per fascicle?
A muscle with fewer myofibrils per muscle fibre or more myofibrils per muscle fibre?
A
- All motor units active
- More muscle fibres per fascicle
- More myofibrils per fibres
3
Q
Describe the percent of muscle tissue in your body by weight
A
Muscle tissue ~50%
Skeletal muscle ~40%
Cardiac and smooth muscle ~10%
Muscle tissue is VERY HEAVY - making up 50% of your body weight
4
Q
What is basal metabolic rate (BMR)?
A
the number of calories the entire body requires to produce enough ATP to maintain all basic functions AT REST
- measure of how much energy the different tissues use
basal = at rest
5
Q
Skeletal muscle tissue makes up how much of the body’s resting metabolic load? (BMR)
A
15% but it goes up as you use your muscles
6
Q
What is catabolism?
A
breakdown of complex molecules
7
Q
What is anaerobic metabolism? (Anaerobic ATP synthesis)
A
METABOLISM WITHOUT OXYGEN
GLYCOLYSIS
- occurs in the CYTOSOL
- ATP generated by the breakdown of glucose, lipids, and other organic molecules WITHOUT OXYGEN
- glucose gets broken down to pyruvate
8
Q
What is aerobic metabolism? (Aerobic ATP synthesis)
A
METABOLISM WITH OXYGEN
AEROBIC METABOLISM/(CAC + ETC)
- occurs in the MITOCHONDRIA
- ATP generated by breakdown of glucose, lipids, or other organic molecules WITH OXYGEN
- more complete breakdown inside the mitochondria
- takes in pyruvate or fatty acids and breaks them down into CO2 and H2O
9
Q
What is glycolysis
A
ANAEROBIC METABOLISM
- anaerobic breakdown of glucose to pyruvate in the cytosol of a cell
- does not require oxygen
- provides a net gain of 2 ATP molecules
- generates pyruvate molecules from each glucose molecule
10
Q
What is aerobic metabolism?
A
- occurs in the mitochondria
- requires oxygen
- oxygen, ADP, phosphate ions, and organic substrates such as pyruvate are absorbed into mitochondria
- very efficient process
11
Q
What is the trade-off that exists between the total amount of ATP generated and the rate at which it can obtained?
A
- Aerobic metabolism
- HIGHLY EFFICIENT
- VERY SLOW
- REQUIRES A STEADY OXYGEN SUPPLY
- more than 30 (~36) ATP molecules are produced from every glucose that goes through the mitochondria
- can also use fatty acids - Anaerobic metabolism
- NOT VERY EFFICIENT BUT VERY FAST
- DOES NOT NEED OXYGEN
- ONLY PRODUCES 2 ATP MOLECULES
- cannot get ATP from fatty acids without aerobic metabolism - Phosphocreatine
- DOES NOT NEED OXYGEN
- VERY VERY FAST
- LIMITED STORES IN MUSCLE (RAPIDLY DEPLETED)
12
Q
What is phosphocreatine?
A
- takes a phosphate from ATP and makes phosphocreatine
- phosphocreatine can be stored so that if you need ATP, you can get the phosphate off the phosphocreatine onto an ADP to make ATP
- very limited because you do not have that much creatine in the muscle fibres
- keeps the muscle going for a few moments (rapid depletion)
13
Q
Summarize the trade between aerobic metabolism, anaerobic metabolism, phosphocreatine
A
Aerobic metabolism - slow but produces lots of ATP
Anaerobic metabolism - fast but produces very little ATP
Phosphocreatine - very fast but very limited
14
Q
What are the three levels of activity for muscle metabolism?
A
- Muscles at rest
- Muscle at moderate activity
- Muscle at peak activity
15
Q
Describe the metabolism of a muscle at rest
A
- demand for ATP is low
- more than enough oxygen is available for the mitochondria to meet that demand and they produce a surplus of ATP
- extra ATP is used to build up reserves of creatine phosphate and glycogen
- can absorb fatty acids and glucose delivered by the bloodstream
- aerobic respiration of FFA
- fatty acids are broken down in the mitochondria, generating ATP that is used to convert creatine to creatine phosphate and glucose to glycogen
16
Q
Describe the metabolism of a muscle at moderate activity levels
A
- demand for ATP increases
- rate of oxygen consumption increases -> muscle is mostly relying on aerobic metabolism of pyruvate to generate ATP
- pyruvate is provided by glycolysis (anaerobic metabolism) and using glucose from glycogen reserves
- aerobic respiration of FFAs and glucose
- muscle will not become fatigued as long as there is enough glycogen, lipid, and amino acid reserves
17
Q
Describe the metabolism of a muscle at peak activity levels
A
- most or all myofibrils are active (aerobic + anaerobic respiration of glucose and CP conversion)
- too much ATP needed in a unit of time than a mitochondria can handle
- substantial demand for ATP and mitochondrial ATP production is maximized according to the availability of oxygen -> oxygen levels decrease and mitochondria turns off
- mitochondria can provide only 1/3 of the ATP needed at peak activity
- SWITCH TO ANAEROBIC METABOLISM
- glycolysis produces the 2/3 rest
- glycolysis produces more pyruvate faster than can be utilized in the mitochondria, pyruvate levels rise in the cytosol
- since oxygen is limited, pyruvate is converted to lactate and the breakdown of ATP during muscle contraction releases H+ ions
- build up of waste products
18
Q
Compare muscles at rest, moderate activity, and peak activity
A
Resting - aerobic respiration, creating glycogen and creatine phosphate reserves to store ATP (excess oxygen)
Moderately active - aerobic respiration of FFAs and glucose (still enough oxygen)
Peak activity - some aerobic respiration, but switches over to anaerobic respiration because there is not enough oxygen, produces waste products
19
Q
How do you differentiate at rest, moderately active, and peak activity muscles (in brief)?
A
Peak - you would see glucose and creatine phosphate being broken down, waste products (lactate and creatine) build up
Moderately active - no waste products being produced (lactate or creatine), using fatty acids and glucose
Rest - only using fatty acids, producing glycogen and CP stores
20
Q
When is ATP required in the excitation-contraction coupling mechanism?
A
Excitation and contraction in skeletal muscles are both multi-step processes, and require ongoing energy input to maintain
REQUIRE STEADY SUPPLIES OF ATP
- Neural control - requires ATP to dump neurotransmitters (acetylcholine) and restore conditions
- Excitation - requires ATP to power the Na+/K+ pump moving ions back and forth
- Calcium ion release - requires ATP to get calcium back into the SR pump
- Contraction cycle begins - requires ATP to contract the muscles (recock the myosin head)
21
Q
ATP is required for [______] than just the contraction cycle - it is also required to maintain the processes that support myofibre [________________].
A
ATP is required for more than just the
contraction cycle – it is also required to maintain the processes that support myofibre excitation.
22
Q
What is muscle fatigue?
A
- rapid ATP production affects the ability of muscles to initiate or maintain the contraction cycle
- reduced contractile tension for the same (excitation) stimulus
- not as much force for the same excitation stimulus = muscles getting weaker
23
Q
What fatigue factors affect excitation processes in skeletal muscle?
A
- Depletion of ACh vesicles in motor neuron axon terminal
- Accumulation of K+ in the T-tubules (ECF) due to repeated APs
- Leakage of Ca2+ back into the sarcoplasm
- Microtears in myofibrils
- Build-up of lactate and H+
24
Q
What is rigor mortis?
A
The stiffness of the muscles and joints of the body after the death of an individual
Rigor mortis is a natural process that occurs in a dead body. It’s when the muscles in the body become stiff and rigid. This happens because, after death, the cells in the muscles can’t get the energy they need to relax, so they stay contracted, making the body stiff.
25
Describe how the depletion of ACh vesicles in the motor neuron axon terminal causes muscle fatigue.
during prolonged muscle activity, the motor neuron may be releasing more Ach from the vesicles than can be replenished
a decrease in ACh vesicles means that the motor neuron cannot release sufficient ACh into the synaptic cleft
muscle contractions decrease
26
Describe how an accumulation of K+ in the T-tubules (ECF) due to repeated APs causes muscle fatigue.
in an action potential, sodium ions rush into the cell and potassium ions are rushed out of the cell (ECF)
in order to bring the action potential back down, potassium ions must rush back in
so an accumulated potassium can throw off the ability to produce more action potentials
27
Describe how leakage of Ca2+ back into the sarcoplasm causes muscle fatigue.
- non-ideal amounts of calcium
- when muscles are supposed to relax but the Ca2+ leakage prevents that from happening
- calcium is released from T-tubules into sarcoplasm for contractions to happen, and then they should be pumped back into the SR (active transport) to end contractions
- calcium ends up outside the sarcoplasm when it shouldn't be there
28
Describe how microtears in myofibrils causes muscle fatigue.
- overworking the muscles can cause microtears in the muscles/myofibrils
as you go through anaerobic metabolism, you get a build-up of waste products that makes the sarcoplasm acidic
- accelerates the problem of microtears
- interacts with other fatigue factors and leads to damage in myofibrils
29
Describe how the build-up of lactate and H+ causes muscle fatigue.
when you mess with the pH, it tends to inhibit/throw off proteins so it messes with how myosin and actin interact
- insufficient interaction
- prone to tear
30
What is the main fatigue factor that affects contraction processes in skeletal muscle?
Leakage of Ca2+ back into the sarcoplasm
31
How does rigor mortis differ from muscle fatigue?
Fatigue isn't rigor mortis! Homeostatic processes trigger reductions in muscle activation long before myofiber ATP stores would actually run out
- fatigue is more about muscles not producing tensions when you want them to
- rigor mortis is when muscles in the body cannot get the ATP to relax after death so they remain stiffened/contracted
32
How do muscles recover from fatigue?
- muscle recovery from fatigue takes time and requires coordination with other organ systems, especially the liver
33
How do muscles recover from fatigue short term?
They REST
At rest, lactate (waste from anaerobic metabolism) can be used in aerobic metabolism or shipped to the liver for gluconeogenesis
Lactate can be changed back to pyruvate and then used to produce ATP in the liver
Pyruvate can be changed back to glucose/glycogen in the muscle (stores)
34
How do muscles recover from fatigue med/long term?
Myosatellite cells are activated and proliferate, utilizing supplies of free amino acids in the blood to rebuild torn myofibrils
Microtears trigger the myosatellite cells to proliferate, activate, and produce their own myofibrils to rebuild
35
What is gluconeogenesis?
the metabolic process by which glucose is formed from noncarbohydrate sources, such as lactate, amino acids, and glycerol
36
What is the trade-off between maximal tension production and energy efficiency?
Maintaining the contraction cycle requires a steady supply of ATP for every participating myosin head
If you add more myofibrils to maximize tension production, there is not enough mitochondria to support the contractions and you risk rapid fatigue
more myofibrils = more power
more myofibrils = less room for other organelles (mitochondria to supply ATP)
peak tension or rapid fatigue?
more power = less long-term endurance
37
Summarize the trade-off between tension and fatigue in muscles:
Muscles can generate high tension for SHORT durations
However, as muscles CONTRACT CONTINOUSLY, they become FATIGUED, and their ability to produce max tension DECREASES
There's an INVERSE relationship between the DURATION of sustained tension and the force that can be produced
In other words, as the DURATIOof muscle activity increases, the force a muscle can generate typically decreases due to the onset of fatigue.
DURATION OF MUSCLE ACTIVITY INCREASES = FORCE A MUSCLE CAN PRODUCE DECREASES DUE TO FATIGUE
38
Describe a twitch contraction
1. Latent period
2. Contraction phase
- max tension development
3. Relaxation phase
giving the muscle a single AP = single twitch stimulus
39
How do twitches in different muscles compare?
Different muscles produce different looking twitches
- stimulus is the same but the pattern of the twitch is different
40
What determines the characteristics of a muscle's twitch?
The anatomical and physiological properties of their MUSCLE FIBRES
1. timing
2. protein composition
3. organelle/tissue composition
41
How does timing determine a muscle's twitch?
1. Fast, short twitches
2. Slow, prolonged twitches
42
How does the protein composition of myofibres determine twitch?
Different types of myosin go through contraction cycles faster or slower
Same with calcium pumps
43
How does the organelle/tissue composition of a myofibre determine twitch?
1. Fast, short twitches
- fast calcium pump (reset contractions)
- low capillaries
- large diameter (velocity)
- few mitochondria
2. Slow, prolonged twitches
- lots of mitochondria
- high capillaries
- slow calcium pump (reset contractions)
- small diameter (velocity)
44
Would a muscle have different types of fibres or just one type?
Vast majority of muscles have more than one type - only a small amount of muscles only have one type of fibre
45
What are the two types of muscle fibres?
Type I
Type II
- subtypes:
Type II A
Type II B
46
What are Type I fibres?
SLOW TWITCH OR SLOW-OXIDATIVE FIBRES
1. fewer myofibrils but more mitochondria per fibre
- cannot make a lot of tension
- more aerobic capacity
2. slow myosins and slow pumps
- myosin that goes through the contraction cycle slowly
- calcium pumps take calcium out of the sarcoplasm and into SR slowly
- sustained twitch
- relatively slow
3. more capillaries per fibres
- small diameter
- keep going without producing waste products
- higher/steadier oxygen supply for aerobic metabolism
47
Type I fibres are not __________ but they are _______________
[trade-off between power and fatigue]
Type I fibres are NOT POWERFUL but they ARE FATIGUE RESISTANT
48
What are Type II fibres?
FAST TWITCH FIBRES
1. More myofibrils per fibre but fewer mitochondria
- higher maximum tension
- lower aerobic capacity
2. Fast myosin and fast pumps
- maximal twitch tension develops quickly but is not long in duration
- makes a lot of tension very quickly but fatigues easily
3. Fewer capillaries per fibre
- lower oxygen supply -> anaerobic metabolism
- higher levels of creatine phosphate
- given up oxygen supply to maximize tension
49
Type II fibres produce high __________and _____________ BUT they __________ easily.
[trade-off between power and fatigue]
Type II fibres produce HIGH FORCES AND RAPID CONTRACTIONS BUT they FATIGUE EASILY
50
What are the two subtypes of Type II fibres?
Type II B
- fast glycolytic fibres
Type II A
- fast-oxidative fibres
51
What are Type IIB fibres?
fast-glycolytic fibres (fast-fast)
52
What are Type IIA fibres?
fast-oxidative fibres (intermediate)
- midpoint between I and IIB but closer to I fibres
- takes a little longer to recover than IIB
- fast contraction speeds
- intermediate twitch durations
- intermediate size/and power
- intermediate mitochondria and capillary density
- intermediate resistance/recovery from fatigue
53
Compare Type I, Type IIB and Type IIA muscle fibres
Type I: slow twitches - not powerful but fatigue resistant
Type IIB: fast-glycolytic fibres - high forces and rapid contractions but fatigue easily
Type IIA: fast-oxidative fibres - intermediate between Type I and Type IIB
54
What kind of muscle fibre would be advantageous for marathon runners?
Marathons - long term endurance
- requires fibres that are fatigue resistant
Type I
55
What kind of muscle fibre would be advantageous for swimmers?
Swimmers - somewhere between long term endurance and short term max energy
- requires some intermediate
Type IIA
56
What kind of muscle fibre would be advantageous for sprinters?
Sprinters - short, quick maximum energy
- requires fibres that can produce maximal tension very quickly
Type IIB
57
Explain why someone with a muscle fibre composition that gives them an advantage in marathon might struggle in a sprint race or vice versa
Marathon runners with Type I have muscle fibres that are fatigue resistant but produces much slower twitches, so they wouldn't be advantageous in short-distance, fast sprint races.
On the other hand, sprint racers with type IIB would have muscle fibres that are fast but fatigue easily. They would not be able to run long distance in a marathon because their muscle fibers are not right for prolonged exercise
58
What are motor units
Muscle fibres are organized into motor units
The combination of an individual motor neuron and all of the muscle fibers that it innervates is called a motor unit
- a muscle fibre has ONE single neuromuscular junction (NMJ)
- a single motor neuron can make NMJs with anywhere between 1-1000 muscle fibres
59
Each motor unit's activation (of fibres) is _____________________
ALL OR NONE
- when it comes to activating motor units, it either activates ALL OF THE FIBRES in the unit or NONE AT ALL!
- but NOT ALL MOTOR UNITS HAVE TO BE ACTIVATED in a contraction
- the amount of motor units activated differ with levels of muscle tension
60
All fibres in a motor unit are of the _____________ type and fibre type correlates with number of fibres per unit
All fibres in a motor unit are of the SAME FIBRE TYPE and fibre type correlates with number of fibres per unit
Both the number of myofibrils per fibre and the number of myofibres per motor unit contribute to the tension generated when that unit is recruited
REMEMBER: muscles have mixed fibres but motor units do not have mixed fibers
- usually sorted by size
61
Small motor units:
Fibres?
Type?
Small motor units:
Few fibres,
All Type I
62
Largest motor units:
Fibres?
Type?
Largest motor units:
Many fibres,
All Type IIB
63
True or False: All fibres in a motor unit are of the same fibre type
True
64
True of False: All fibres in a muscle have to be the same type
False - there is often a variety of fibre types in a muscle, only a few muscles are made of the same type of fibre
65
What is the Size Principle?
Only the smallest motor units will be recruited by weak stimuli in the spinal cord, while strong stimuli recruit both small, medium, and large motor units
Weak stimuli - small motor units
Strong stimuli - all the above
- your body will only recruit the smaller units unless you really need the larger ones
as you turn up stimulus strength, you can get more tension out of the motor units
66
Motor neuron activation occurs in the _______________ and is organized so that the largest motor units are recruited by the __________ stimuli.
Motor neuron activation occurs in the SPINAL CORD and is organized so that the largest motor units are recruited by the STRONGEST stimuli.
67
What is asynchronous recruitment?
Asynchronous - not all on at the same time
Occurs during SUSTAINED CONTRACTION
- no unit is constantly activated
you cannot maintain peak tension for a long time, but you can maintain it at a level just below peak tension
- individual motor units take turns
- turning on and off to maintain tension
68
What is the relative size of slow-oxidative fibers? And their type?
SMALLEST
Type I
69
What is the relative size of fast-oxidative fibers? And their type?
MEDIUM/INTERMEDIATE
Type IIA
70
What is the relative size of fast-glycolytic fibers? And their type?
LARGEST (in terms of numbers)
- individual fibers
- more fibers per motor unit
- contributes to how much tension/force you can get out of each motor unit
Type IIB
71
How do muscles become larger? What is the benefit of muscles becoming larger?
Muscles can enhance their peak tension production by becoming larger
Muscles can become larger in two ways:
1. Hyperplasia
2. Hypertrophy
72
What is hyperplasia?
- adding more MYOFIBRES into the FASCICLES
- more myofibres per fascicle
- adding more cells
73
What is hypertrophy?
- adding more MYOFIBRILS into the MYOFIBRES
- more myofibrils per myofibre
74
Hyperplasia or Hypertrophy?
ADDING MYOFIBRES INTO FASCICLES
HYPERPLASIA
75
Hyperplasia or Hypertrophy?
ADDING MORE MYOFIBRILS INTO MYOFIBRES
HYPERTROPHY
76
Adults can only increase their muscles in one way, is it hyperplasia or hypertrophy? Explain why.
Adults can increase their muscle size through HYPERTROPHY, but NOT THROUGH HYPERPLASIA
- you cannot add new myofibres after embryonic development
- skeletal muscles can repair muscle fibres but cannot add new ones
- myosatellite cells repair myofibrils
- physical training increases fibre diameter, not fibre number
77
Compare and contrast aerobic to anaerobic training
Aerobic training - leads to hypertrophy of Type I fibres
Anaerobic (high intensity - think HIIT) training - leads to hypertrophy of Type IIB fibres
78
Specific training regimes can target one fibre ______ over another, but fibre __________ is very rare
Specific training regimes can target one fibre TYPE over another, but fibre CONVERSION is very rare
79
**What are two changes that you could predict you would see in skeletal muscle biopsies before and after someone begins body building?
1. Hypertrophy - there would be MORE MYOFIBRILS PER MYOFIBRE before and after they began body building
2. In order to body build, you want to become STRONGER for short-durations (Type IIB fibres) so there would be MORE TYPE IIB FIBRES in the biopsy before and after they began body building
80
**What is the trade-off existing between muscle size and sarcomere length?
Larger muscles add weight,
take up more room,
and use more energy even at rest
81
How does the organization of muscle fascicles affect the amount of force produced for a given muscle volume?
What are the three types of organization of muscle fascicles?
1. Parallel muscle
2. Convergent muscle
3. Pennate muscle
82
How do muscles function?
Muscles require ATP to maintain contraction which can produced via anaerobic or aerobic forms of metabolism
The type of metabolism they us varies based on the current energy demands
If current energy demand exceeds the ATP-generation capacity, fatigue can result
83
What are the three distinct types of muscle fibres?
Type I
- slow, weaker but fatigue-resistant fibres
Type IIA
- intermediate between Type I and Type IIB
Type IIB
- powerful fast fatiguable fibres
84
In adults, muscles grow through addition of ___________ not ___________ but some capacity for conversion between different fibre types does exist
In adults, muscles grow through addition of MYOFIBRILS not MYOFIBRES but some capacity for conversion between different fibre types does exist
85
Conversion is only possible between these two types of muscle fibres:
Conversion between Type IIA and Type IIB is POSSIBLE
86
Conversion is NEVER possible between these two types of muscle fibres:
Conversion between Type I and Type II is thought to NOT BE POSSIBLE
87
What is the trade-off between muscle and musculoskeletal organizations?
A trade-off between force generation and the ability to efficiently produce or modify movement
88
Are all muscles made equal?
A. Skeletal and cardiac muscle tissue contain sarcomeres, but smooth muscle is NOT arranged into sarcomeres
B. Force generation is PROPORTIONAL to muscle cross-sectional area (more area = more force!)
C. The faster a muscle experiences twitches, the more force they can generate, but they fatigue easily (Slower twitch fibres generate less force but are fatigue resistant)
D. Anaerobic metabolism is faster BUT NOT MORE EFFICIENT than aerobic metabolism (very fast but does not produce a lot of ATP)
E. Aerobic metabolism is associated with a build-up of lactate/waste products (H+)
F. Large motor units contain high % of Type IIB fibres / small motor units contain high % of Type I fibres
