muscle function and metabolism Flashcards
Name 3 locations where ATP is used during muscle contraction
cross bridge cycle, to clear calcium from sarcomere, to maintain resting membrane potential
What locations within a muscle cell could sarcomeres
be added in increases muscle force?
sarcomeres added in parallel to each other
How does acetylcholine release into the NMJ lead to
muscle contraction?
- ACh into neuromuscular junction
- ACh diffuse across NMJ and bind to ligand gated channels on muscle causing depolarization on muscle.
- action potential propogate through sarcomere to t-tubules
- releases Ca2+ from sarcoplasmic reticulum to sarcomere
- Ca2+ bind to troponin removing tropomyosin from actin/myosin binding site on troponin
- cross bridge cycling can occur where leftover ADP and Pi are attached. Myosin binds to actin, Pi is released strengthening the bond, ADP released in power stroke, ATP bind releasing myosin from actin, ATP hydrolysed to ADP and Pi cocking myosin head.
How does muscle contraction stop?
- Stimulation ceases
- calcium stop being released into sarcoplasmic reticulum;.
- remaining Ca2+ transported back to sarcoplasmic reticulum via active transport using ATP
- tropomyosin covers binding sites on actin if ATP is present to detach them.
What are the advantages and disadvantages of
increasing the angle of pennation in a muscle?
Increasing the pennation in the muscle increases the angle of the muscle fibre in relation to the tendon that they attach to. This allows more sarcomeres to fit in parallel which increase force producing capacity
What are the advantages of a longer fascicle length
With a longer fascicle
- can work through greater range of motion
- amount of sarcomeres in series can move the joint at a faster velocity
- if there is more muscle belly and less tendon, the muscle takes less time to pull the slack from the tendon meaning the preloading phase of a jump can be shorter
Explain how adding sarcomeres in series and parallel
would alter muscle force production characteristics
- Adding sarcomeres in series will increase the amount of shortening/lengthening the muscle can do and therefore can increase the velocity that of rotation around the joint
- sarcomeres in parallel will mean that the forces on the joint are being distributed across more sarcomeres, increases the force producing capabilities.
Athlete A has 60% type I fibers Athlete B has 60%
type II fibers. Explain the mechanism which would
affect their performance in the 100 M dash and
10,000 M race.
- The athlete having more type II fibres better at rapidly using ATP to contract/relax,
- use more phosphocreatine and fast glycolysis, (convert ADP and phosphocreatine to ATP and Creatine, and convert glucose to pyruvate in cytoplasm of muscle cells, then turn that pyruvate to lactate).
- this will benefit them in the 100M dash
- the athlete having more type I fibers would be better at using aerobic glycolysis to fully oxidize glycerol and glucose, and beta oxidation to make make reduced co-enzymes such as NADH+H^+ and will overall be more efficient at making ATP. They will also be better able to utilize lactate produced by type II fibers by taking it into the blood stream to a type I fiber which will metabolize it giving two H+’s to NAD+ converting lactate to pyruvate which can then undergo aerobic glycolysis, and will not fatigue as fast due to less accumulation of lactic acid.
- this will be better for the 10,000M race.
How would calcium concentrations in the muscle change during twitch, unfused tetanus and fused tetanus
contraction?
during a twitch, calcium in the sarcomere would enter an leave completely
during unfused tetanus, calcium enters and doesn’t completely leave, before more calcium enters after next impulse,
in a fused tetanus, the action potentials come so fast that no calcium leaves the sarcomere making for a continuous contraction
What mechanism differentiate fused and unfused tetanus?
With fused and unfused tetanus, action potential frequency determines how much calcium is cleared from the sarcomere via active transport and dissociation before the next action potential.
If there are frequent enough action potentials, the sarcoplasmic reticulum keeps releasing calcium and calcium stays in the sarcomere for cross bridge cycling to continue. This is a fused tetanus. If action potentials are infrequent enough, some calcium dissociates, and gets transported back into the sarcoplasmic reticulum before next action potential.
Why do type II fibers fatigue more quickly?
Type II fibers have fewer mitochondria and rely mostly on anaerobic metabolism which creates H+ ions and lactate as a byproduct leading to fatigue. (can further explain about glocose to pyruvate to lactate).
You hold an isometric bicep curl with 30% of your 1RM.
Explain which motor units would likely be recruited.
Would this change if held the contraction until you were
forced to drop the weight due to fatigue?
You would start with smaller motor units which contain fewer muscle fibers and mostly type I muscle fibers. As those motor units start to fatigue, you would start to recruit larger motor units with larger axons, containing more muscle fibers and more type II fibers which have more force producing capabilities. Finally once those are fatigued, the weight would drop as your muscles can not meet the ATP needs to keep the weight up.
What are the main factors which explain sex differences
in strength?
Total cross sectional area - men tend to have much more upper body cross sectional area, lower body is closer (sometimes women are better as shown in graph)
- strength per unit of cross sectional area is about the same, its more about amount of cross sectional area.
On absolute basis, men are stronger in all muscle group, when normalizing for body weight, fat free mass, or total cross sectional area, men and women are near identical in strength
Men tend to have more type II fibers which are better for force production
Women also have more fat mass therefore total body weight not as accurate.
What is the best way to correct for muscle size when
comparing strength between people?
Allometric scaling, this follows a curve that takes into account the differences in peoples relative strength as size goes up.
The curve is: body weight^2/3
This is necessary because when you get larger, you don’t get stronger proportionally, this is because muscle cross sectional area determines strength which is a squared metric, and volume is a cubed metric, therefore you must get a lot larger to only get a little stronger.
Why do successful Olympic rock climbers tend to be small
and lean rather than larger and lean?
Because the relationship between muscle volume (cubic metric) and muscle cross sectional area (squared metric) is not linear, muscle volume must go up much more for cross section to go up a little. Specifically, to measure this you can use allometric scaling which is: body weight^2/3.
This means smaller people tend to have a better power to weight ratio which is crucial for sports where gravity is a limiting factor e.g. rock climbing.
