Skeletal Muscle Function

Question 1

Q: What are the four primary functions of skeletal muscle?

Answer 1

A: Movement , maintaining posture , stabilizing joints , and thermogenesis (generating heat).

Question 2

Q: What are the components of skeletal muscle organization from largest to smallest unit?

Answer 2

A: Skeletal muscle → Muscle fascicle → Muscle fiber (multinucleated cell) → Myofibril (organelle) → Sarcomere (contractile unit).

Question 3

Q: What is the plasma membrane of a skeletal muscle cell called?

Answer 3

A: The Sarcolemma.

Question 4

Q: What is the primary function of the Sarcoplasmic Reticulum (SR)?

Answer 4

A: To act as the storage site for Ca2+ ions.

Question 5

Q: What structure is formed by the T-tubule and the terminal cisternae of the SR?

Answer 5

A: The Triad.

Question 6

Q: What is the function of a Satellite cell?

Answer 6

A: It is a muscle stem cell responsible for postnatal muscle growth, hypertrophy, and regeneration.

Question 7

Q: What are the thick and thin filaments of the sarcomere?

Answer 7

A: Thick filament is Myosin and Thin filament is Actin.

Question 8

Q: What is the function of Titin?

Answer 8

A: An elastic protein that connects thick filaments (Myosin) to the Z line.

Question 9

Q: What is the Z line/disc?

Answer 9

A: The boundary of a single sarcomere and the attachment site for thin filaments.

Question 10

Q: Which band of the sarcomere is referred to as “Anisotropic” and contains the full length of the thick filaments?

Answer 10

A: The A band.

Question 11

Q: Which band of the sarcomere is referred to as “Isotropic” and contains only thin filaments?

Answer 11

A: The I band.

Question 12

Q: Which band is the “Heller” (brighter) region within the A band that contains only thick filaments and shortens during contraction?

Answer 12

A: The H band.

Question 13

Q: What are the two key receptors involved in excitation-contraction coupling?

Answer 13

A: The Dihydropyridine (DHP) receptor (a voltage-gated Ca2+ channel) and the Ryanodine Receptor (RyR) (a Ca2+ channel).

Question 14

Q: What does the binding of Ca2+ ions to the thin filament trigger?

Answer 14

A: Ca2+ binds to the Troponin complex , causing Tropomyosin to move, which exposes the Myosin-binding sites on Actin.

Question 15

Q: What molecule is needed for the myosin head to detach from actin (cross-bridge release)?

Answer 15

A: ATP.

Question 16

Q: What molecular event causes rigor mortis (“Rigor”)?

Answer 16

A: The absence of ATP prevents the Myosin head from detaching from Actin after the power stroke, maintaining the cross-bridge.

Question 17

Q: What is the function of SERCA?

Answer 17

A: Sarco-Endoplasmic Reticulum Calcium ATPase. Its function is to reaccumulate Ca2+ ions back into the SR during the relaxation phase.

Question 18

Q: What are the three primary types of muscle contraction?

Answer 18

A: Concentric (shortening), Eccentric (elongation), and Isometric (no change in length).

Question 19

Q: Which type of contraction does not result in a shortening of the muscle-tendon unit?

Answer 19

A: Isometric contraction.

Question 20

Q: Which type of contraction generally produces more output force?

Answer 20

A: Eccentric contraction (elongation).

Question 21

Q: Why do eccentric contractions produce more force and consume less ATP than concentric ones?

Answer 21

A: Titin elongation contributes passively to tension, and fewer cross-bridges are needed as they act like brakes to resist elongation.

Question 22

Q: What is the force-velocity relationship for concentric contraction?

Answer 22

A: It is a trade-off: the faster the concentric contraction, the less the output force.

Question 23

Q: What are the three main energy systems for muscle contraction?

Answer 23

A: The Phosphagen System (ATP-creatine phosphate), Anaerobic System (Glycolysis) , and Aerobic System (Oxidative Phosphorylation/Krebs cycle).

Question 24

Q: Which energy system provides immediate energy and lasts for about 8−10 seconds (e.g., 100m sprint)?

Answer 24

A: The Phosphagen System.

Question 25

Q: Which energy system is the primary source for activity lasting 1−2 minutes?

Answer 25

A: The Anaerobic System (Glycolysis).

Question 26

Q: What are the characteristics of Type 1 (slow oxidative) muscle fibers?

Answer 26

A: Slow contraction speed, small motor unit, uses oxidative phosphorylation (aerobic), has many mitochondria, high myoglobin (red muscle), and a slow rate of fatigue.

Question 27

Q: What is the difference between Central fatigue and Peripheral fatigue?

Answer 27

A: Central fatigue is of neural origin (decreased mental drive to fire motor neurons). Peripheral fatigue acts at or downstream of the NMJ , caused by depletion of phosphagens/glycogen or accumulation of metabolites (e.g., H+, lactate, Pi​).