Lecture 5 - Skeletal Muscle Contraction Flashcards
In the sliding filament mechanism, what event follows the opening of ryanodine receptor calcium channels and release of calcium from the sarcoplasmic reticulum?
Binding of calcium to troponin.
What is the first event of the sliding filament mechanism?
Arrival of action potential to the end of the nerve fiber.
In the sliding filament mechanism, what event follows the cleavage of ATP into ADP and inorganic phosphate, recocking the myosin head?
Binding of myosin head back to the actin active site. Cycle continues until intracellular calcium is resequestered into the sarcoplasmic reticulum.
In the sliding filament mechanism, what event follows the interaction of voltage-gated DHP channels in T-tubules with ryanodine receptors on the sarcoplasmic reticulum.
Ryanodine receptor calcium channels open releasing calcium from the sarcoplasmic reticulum.
Intracellular calcium raises form 0.1 umol/L to 10 umol/L.
In the sliding filament mechanism, what event follows the conformation change of troponin pulling tropomyosin away from active sites on actin?
Binding of myosin heads to active sites on actin.
In the sliding filament mechanism, what event follows the binding of ATP to myosin and the head releasing from the actin active site.
Cleavage of ATP into ADP and inorganic phosphate, recocking the myosin head.
What is concentric contraction?
Isotonic contraction where the muscle shortens.
Describe summation.
When electrical simulation occurs faster than mechanical events. Calcium concentration increases and muscle tension continually increases.
In the sliding filament mechanism, what event follows the opening of voltage-gated sodium channels on the sarcolemma and conduction of an action potential along the sarcolemma?
Interaction of voltage-gated DHP channels in T-tubules with ryanodine receptors on the sarcoplasmic reticulum.
In the sliding filament mechanism, what event follows the arrival of the action potential to the end of the nerve fiber?
Opening of voltage gated calcium channels on the end of the nerve fiber.
What is eccentric contraction?
Isotonic contraction where the muscle lengthens.
What does SERCA do?
Uses ATP to pump calcium from the cytosol back into the SR.
Sarcoplasmic Reticulum Calcium ATPase
What is located in the middle of a third class lever? Compare the directions of the forces.
In-force is in the middle.
Forces are in the same direction.
Ex. Lifting a weight in the palm of your hand
What is isometric contraction?
Contraction where tension increases but there is no increase in length.
What are dihydropyridine (DHP) receptors?
Voltage gated calcium channels located in the sarcolemma of T-tubules.
Causes a conformational change in ryanodine receptors.
Allows a trace amount of calcium into the cytosol.
Neurons innervated myofibers of the same _______________.
Type (slow or fast)
Describe the hierarchical organization of skeletal muscle.
Myofilament (actin myosin filaments that make up a sacromere) -> myofibril (chain of sarcomeres) -> myofiber (muscle cell containing many myofibrils) -> sarcolemma (cell membrane of myofiber) -> endomysium (connective tissue surrounding each myofiber) -> fascicle (bundle of myofibers) -> perimysium (connective tissue surrounding each fascicle) -> muscle (multiple fascicles) -> epimysium (connective tissue around each muscle
What are the different banding patterns of a sarcomere?
Z line/disc, I bands, A bands, and H bands
What is isotonic contraction?
Contraction where there is a change in length.
In the sliding filament mechanism, what event follows the binding of calcium to troponin?
Conformation change of troponin pulling tropomyosin away from active sites on actin.
In the sliding filament mechanism, what event follows release of acetylcholine (Ach) into the synaptic cleft?
Opening of ligand gated sodium channels in the sarcolemma.
What are the H bands and what happens to them during contraction?
They are composed entirely of myosin. It is the portion of the A band which is not overlapped by actin.
They shrink almost to the point they disappear during contraction.
The number of myofibers ________ be increased.
The number of myofibrils ________ be increased.
Loss of muscle tissue will result in ________.
Cannot; can; scar tissue
What is located in the middle of a first class lever? Compare the directions of the forces.
Fulcrum is in the middle.
Forces are in opposite directions.
ex. raising the jaw
In the sliding filament mechanism, what event follows opening of ligand-gated sodium channels in the sarcolemma?
Opening of voltage-gated sodium channels in the sarcolemma and conduction of an action potential along the sarcolemma.
What are the I bands and what happens to them during contraction?
They are located at the outside of each sarcomere and are split in half by the Z lines. Composed entirely of actin.
They get smaller during contraction.
What are Z lines and what happens to them during contraction?
They are the borders of each sarcomere.
They come closer together during contraction.
What does calsequestrin do?
Sequesters calcium in the SR reducing the calcium concentration making it easier to pump calcium in.
What is a sarcomere?
The functional unit of contraction in a myofiber.
In the sliding filament mechanism, what event follows the binding of myosin heads to active sites on actin?
The release of organic phosphate and subsequent release of ADP.
What are ryanodine receptors?
Calcium channels in the sarcoplasmic reticulum.
Release calcium in response to conformational change in DHP.
In the sliding filament mechanism, what event follows the release of organic phosphate and subsequent release of ADP?
The power stroke.
What are the characteristics about light, fast twitch fibers (white fibers)?
- faster movement
- lower endurance
- fewer mitochondria
- primarily uses anaerobic respiration resulting in lactic acid build up
- little myoglobin
- larger concentrations of ATPase
What is located in the middle of a second class lever? Compare the directions of the forces.
Out-force is in the middle.
Forces are in the same direction.
ex. raising body on ball of foot
In the sliding filament mechanism, what event follows opening of voltage gated calcium channels on the end of the nerve fiber?
Release of acetylcholine (Ach) into the synaptic cleft.
What are the A bands and what happens to them during contraction?
They are composed of actin and myosin and are defined by the length of the myosin filament.
They do no change width during contraction.
In the sliding filament mechanism, what event follows the power stroke?
Binding of ATP to myosin and the head releasing from the actin active site.
What are the characteristics about dark, slow twitch fibers (red fibers)?
- slower movement
- higher endurance
- more mitochondria
- primarily uses aerobic respiration
- more myoglobin
- smaller concentrations of ATPase
Describe tetany.
Electrical events occur so fast the muscle is unable to relax and remains at maximum contraction.
