Skeletal Muscle - Force, Work, and Energy Flashcards
How do muscles enhance their peak tension?
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
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?
- All motor units active
- More muscle fibres per fascicle
- More myofibrils per fibres
Describe the percent of muscle tissue in your body by weight
Muscle tissue ~50%
Skeletal muscle ~40%
Cardiac and smooth muscle ~10%
Muscle tissue is VERY HEAVY - making up 50% of your body weight
What is basal metabolic rate (BMR)?
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
Skeletal muscle tissue makes up how much of the body’s resting metabolic load? (BMR)
15% but it goes up as you use your muscles
What is catabolism?
breakdown of complex molecules
What is anaerobic metabolism? (Anaerobic ATP synthesis)
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
What is aerobic metabolism? (Aerobic ATP synthesis)
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
What is glycolysis
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
What is aerobic metabolism?
- occurs in the mitochondria
- requires oxygen
- oxygen, ADP, phosphate ions, and organic substrates such as pyruvate are absorbed into mitochondria
- very efficient process
What is the trade-off that exists between the total amount of ATP generated and the rate at which it can obtained?
- 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)
What is phosphocreatine?
- 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)
Summarize the trade between aerobic metabolism, anaerobic metabolism, phosphocreatine
Aerobic metabolism - slow but produces lots of ATP
Anaerobic metabolism - fast but produces very little ATP
Phosphocreatine - very fast but very limited
What are the three levels of activity for muscle metabolism?
- Muscles at rest
- Muscle at moderate activity
- Muscle at peak activity
Describe the metabolism of a muscle at rest
- 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
Describe the metabolism of a muscle at moderate activity levels
- 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
Describe the metabolism of a muscle at peak activity levels
- 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
Compare muscles at rest, moderate activity, and peak activity
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
How do you differentiate at rest, moderately active, and peak activity muscles (in brief)?
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
When is ATP required in the excitation-contraction coupling mechanism?
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)
ATP is required for [______] than just the contraction cycle - it is also required to maintain the processes that support myofibre [________________].
ATP is required for more than just the
contraction cycle – it is also required to maintain the processes that support myofibre excitation.
What is muscle fatigue?
- 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
What fatigue factors affect excitation processes in skeletal muscle?
- 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+
What is rigor mortis?
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.
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
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
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
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
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
What is the main fatigue factor that affects contraction processes in skeletal muscle?
Leakage of Ca2+ back into the sarcoplasm
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
How do muscles recover from fatigue?
- muscle recovery from fatigue takes time and requires coordination with other organ systems, especially the liver
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)
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
What is gluconeogenesis?
the metabolic process by which glucose is formed from noncarbohydrate sources, such as lactate, amino acids, and glycerol
