Lecture 5 - Skeletal Muscle Contraction

Question 1

In the sliding filament mechanism, what event follows the opening of ryanodine receptor calcium channels and release of calcium from the sarcoplasmic reticulum?

Answer 1

Binding of calcium to troponin.

Question 2

What is the first event of the sliding filament mechanism?

Answer 2

Arrival of action potential to the end of the nerve fiber.

Question 3

In the sliding filament mechanism, what event follows the cleavage of ATP into ADP and inorganic phosphate, recocking the myosin head?

Answer 3

Binding of myosin head back to the actin active site. Cycle continues until intracellular calcium is resequestered into the sarcoplasmic reticulum.

Question 4

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.

Answer 4

Ryanodine receptor calcium channels open releasing calcium from the sarcoplasmic reticulum.

Intracellular calcium raises form 0.1 umol/L to 10 umol/L.

Question 5

In the sliding filament mechanism, what event follows the conformation change of troponin pulling tropomyosin away from active sites on actin?

Answer 5

Binding of myosin heads to active sites on actin.

Question 6

In the sliding filament mechanism, what event follows the binding of ATP to myosin and the head releasing from the actin active site.

Answer 6

Cleavage of ATP into ADP and inorganic phosphate, recocking the myosin head.

Question 7

What is concentric contraction?

Answer 7

Isotonic contraction where the muscle shortens.

Question 8

Describe summation.

Answer 8

When electrical simulation occurs faster than mechanical events. Calcium concentration increases and muscle tension continually increases.

Question 9

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?

Answer 9

Interaction of voltage-gated DHP channels in T-tubules with ryanodine receptors on the sarcoplasmic reticulum.

Question 10

In the sliding filament mechanism, what event follows the arrival of the action potential to the end of the nerve fiber?

Answer 10

Opening of voltage gated calcium channels on the end of the nerve fiber.

Question 11

What is eccentric contraction?

Answer 11

Isotonic contraction where the muscle lengthens.

Question 12

What does SERCA do?

Answer 12

Uses ATP to pump calcium from the cytosol back into the SR.

Sarcoplasmic Reticulum Calcium ATPase

Question 13

What is located in the middle of a third class lever? Compare the directions of the forces.

Answer 13

In-force is in the middle.

Forces are in the same direction.

Ex. Lifting a weight in the palm of your hand

Question 14

What is isometric contraction?

Answer 14

Contraction where tension increases but there is no increase in length.

Question 15

What are dihydropyridine (DHP) receptors?

Answer 15

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.

Question 16

Neurons innervated myofibers of the same _______________.

Answer 16

Type (slow or fast)

Question 17

Describe the hierarchical organization of skeletal muscle.

Answer 17

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

Question 18

What are the different banding patterns of a sarcomere?

Answer 18

Z line/disc, I bands, A bands, and H bands

Question 19

What is isotonic contraction?

Answer 19

Contraction where there is a change in length.

Question 20

In the sliding filament mechanism, what event follows the binding of calcium to troponin?

Answer 20

Conformation change of troponin pulling tropomyosin away from active sites on actin.

Question 21

In the sliding filament mechanism, what event follows release of acetylcholine (Ach) into the synaptic cleft?

Answer 21

Opening of ligand gated sodium channels in the sarcolemma.

Question 22

What are the H bands and what happens to them during contraction?

Answer 22

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.

Question 23

The number of myofibers ________ be increased.
The number of myofibrils ________ be increased.
Loss of muscle tissue will result in ________.

Answer 23

Cannot; can; scar tissue

Question 24

What is located in the middle of a first class lever? Compare the directions of the forces.

Answer 24

Fulcrum is in the middle.

Forces are in opposite directions.

ex. raising the jaw

Question 25

In the sliding filament mechanism, what event follows opening of ligand-gated sodium channels in the sarcolemma?

Answer 25

Opening of voltage-gated sodium channels in the sarcolemma and conduction of an action potential along the sarcolemma.

Question 26

What are the I bands and what happens to them during contraction?

Answer 26

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.

Question 27

What are Z lines and what happens to them during contraction?

Answer 27

They are the borders of each sarcomere.

They come closer together during contraction.

Question 28

What does calsequestrin do?

Answer 28

Sequesters calcium in the SR reducing the calcium concentration making it easier to pump calcium in.

Question 29

What is a sarcomere?

Answer 29

The functional unit of contraction in a myofiber.

Question 30

In the sliding filament mechanism, what event follows the binding of myosin heads to active sites on actin?

Answer 30

The release of organic phosphate and subsequent release of ADP.

Question 31

What are ryanodine receptors?

Answer 31

Calcium channels in the sarcoplasmic reticulum.

Release calcium in response to conformational change in DHP.

Question 32

In the sliding filament mechanism, what event follows the release of organic phosphate and subsequent release of ADP?

Answer 32

The power stroke.

Question 33

What are the characteristics about light, fast twitch fibers (white fibers)?

Answer 33

• faster movement
• lower endurance
• fewer mitochondria
• primarily uses anaerobic respiration resulting in lactic acid build up
• little myoglobin
• larger concentrations of ATPase

Question 34

What is located in the middle of a second class lever? Compare the directions of the forces.

Answer 34

Out-force is in the middle.

Forces are in the same direction.

ex. raising body on ball of foot

Question 35

In the sliding filament mechanism, what event follows opening of voltage gated calcium channels on the end of the nerve fiber?

Answer 35

Release of acetylcholine (Ach) into the synaptic cleft.

Question 36

What are the A bands and what happens to them during contraction?

Answer 36

They are composed of actin and myosin and are defined by the length of the myosin filament.

They do no change width during contraction.

Question 37

In the sliding filament mechanism, what event follows the power stroke?

Answer 37

Binding of ATP to myosin and the head releasing from the actin active site.

Question 38

What are the characteristics about dark, slow twitch fibers (red fibers)?

Answer 38

• slower movement
• higher endurance
• more mitochondria
• primarily uses aerobic respiration
• more myoglobin
• smaller concentrations of ATPase

Question 39

Describe tetany.

Answer 39

Electrical events occur so fast the muscle is unable to relax and remains at maximum contraction.