Structure
What is a bundle of fascicles encased in?
The perimysium
What are the two filaments in a sarcomere?
Actin and myosin
What is a static contraction?
A contraction in which the myosin cross-bridges form and recycle but don't slide or change length
What is the order of muscle fiber recruitment?
Type I, Type IIa, Type IIx
What do T tubules do?
T tubules are an extension of the sarcolemma that carry AP deep into the muscle fiber
Name the three types of muscle and where they are found in the body
Skeletal, smooth, cardiac
What is a sarcomere?
The basic contractile element of skeletal muscle
What is a dynamic contraction?
A contraction that produces force and changes length of the muscle, and changes the joint angle
All muscle fibers reach their peak power at what percentage of peak force?
20%
What is the physiology behind tetanus?
Tetanus occurs when a muscle fiber is repeatedly and rapidly stimulated and does not have an opportunity to relax between action potentials
What is the structure of muscle from the smallest unit to the largest?
Sarcomere, myofibril, sarcolemma, muscle fiber, fascicle, perimysium, muscle belly, epimysium
What does titin do?
Acts like a spring to stabilize sarcomeres and centers myosin
What is it called when a muscle fiber is restimulated before it has completely relaxed and the second twitch is added on to the first twitch?
Twitch summation
Which muscle fiber type has <300 fibers per motor unit, is slow twitch, and has a contraction speed of 110ms
Type I
Which muscle fiber type fatigues faster?
Type II
What are satellite cells?
Skeletal muscle stem cells that proliferate quickly, aid in injury response, immobilization, training, and muscle growth and development
What happens after the power stroke ends?
ATP attaches to myosin head and myosin detaches from the actin binding site and returns to original position, ADP releases and myosin attaches to another active site further down
When does the muscle contraction stop?
When the AP stops and calcium is pumped back into the SR
Which muscle fiber type has >300 fibers per motor unit, is fast twitch, and has a contraction speed of 50ms
Type II
What does the sodium-potassium pump do?
Maintains the chemical gradient across the sarcolemma and generates the resting membrane potential
What is the function of the sarcolemma?
Explain the sliding filament theory.
AP triggers Ca+ release from SR, Ca+ binds to troponin which moves tropomyosin, cross bridges form, sarcomeres shorten
Explain excitation-contraction coupling starting from the brain to the muscle itself?
AP starts in brain, arrives at axon terminal & releases ACh, ACh crosses synapse & binds to receptors on the sarcolemma, AP travels down sarcolemma and T tubules, triggers Ca+ release from SR, Ca+ enables actin-myosin contraction by binding to troponin
What are three fiber type determinants?
Genetic factors, training factors, aging
What is the oxidative capacity of each muscle fiber type? High, mod. high, and low
Type I - High
Type IIa- Mod High
Type IIx- Low