Bsf Mock Block 2 - Skeletal & Smooth Muscle
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Mock block 2 exam for Touro BSF course - Fall 2010.
Questions and Answers
- 1.
The repeating subunits of a skeletal muscle myofibril that is also known as the basic contractile unit is called a _____.
- A.
Myofilament
- B.
Sarcomere
- C.
Myofiber
- D.
Actin & myosin complex
- E.
Troponin & tropomyosin complex
Correct Answer
B. SarcomereExplanation
A sarcomere is the repeating subunit of a skeletal muscle myofibril that is responsible for muscle contraction. It is considered the basic contractile unit because it contains all the necessary components for muscle contraction, including actin and myosin filaments, as well as regulatory proteins such as troponin and tropomyosin. The interaction between actin and myosin within the sarcomere allows for the sliding of filaments and the generation of force, leading to muscle contraction. Therefore, sarcomere is the correct answer.Rate this question:
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- 2.
Which of the following would you expect to find located within the H band?
- A.
Actin
- B.
Troponin
- C.
Tropomyosin
- D.
Meromyosin
- E.
None of the above
Correct Answer
D. MeromyosinExplanation
Myosin heavy chain – can be cleaved into a rod-like tail called light meromyosin and a globular heavy meromyosin head.
Within the H-band you would not expect to see any thin filaments, only the thick filaments. Therefore A, B, and C can be ruled out.
Meromyosin is a component of myosin, which you would expect to find on thick filaments located inside the H-band.Rate this question:
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- 3.
Which of the following is responsible for blocking the myosin head binding site in a relaxed muscle?
- A.
Tropomyosin
- B.
Troponin T
- C.
Troponin I
- D.
Troponin C
- E.
More than one of the above
Correct Answer
A. TropomyosinExplanation
Tropomyosin – thin, long (~40nm) protein that lies in the F-actin grooves. Tropomyosin molecules bind head-to-tail in order to run the entire length of the F-actin.
Tropomyosin blocks the myosin head binding site on G-actin by partially overlapping it in the resting (i.e. noncontracting) situation.Rate this question:
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- 4.
In skeletal muscle contraction, only the H and I bands shorten.
- A.
True
- B.
False
Correct Answer
A. TrueExplanation
During skeletal muscle contraction, the H and I bands, which are regions within the muscle fibers, shorten. This is due to the sliding filament theory, where the actin filaments slide over the myosin filaments, causing the sarcomeres (the basic functional units of the muscle) to shorten. The H band represents the region of the sarcomere where only myosin filaments are present, and the I band represents the region where only actin filaments are present. As these bands shorten, the sarcomere as a whole contracts, resulting in muscle contraction. Therefore, the statement that only the H and I bands shorten during skeletal muscle contraction is true.Rate this question:
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- 5.
Where would you expect to find a transverse-tubule with its relationship to a sarcomere?
- A.
At the z-disc or z-line
- B.
Z-I junction
- C.
A-I junction
- D.
A-H junction
- E.
H-M junction
Correct Answer
C. A-I junctionExplanation
At the A-I junction, you would expect to find a transverse-tubule with its relationship to a sarcomere. The A-I junction is the area where the A-band and I-band of a sarcomere meet. The transverse-tubules, also known as T-tubules, are invaginations of the sarcolemma (cell membrane) that extend into the muscle fiber. They play a crucial role in transmitting action potentials deep into the muscle fiber, allowing for synchronized muscle contraction. Therefore, it is logical to expect the presence of T-tubules at the A-I junction, where the sarcomere structure is located.Rate this question:
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- 6.
Which of the following best describes sarcoplasmic reticulum?
- A.
Organelle derived from smooth ER that stores potassium
- B.
Organelle derived from smooth ER that stores calcium
- C.
Organelle derived from rough ER that stores potassium
- D.
Organelle derived from rough ER that stores calcium
Correct Answer
B. Organelle derived from smooth ER that stores calciumExplanation
The sarcoplasmic reticulum is an organelle derived from smooth ER that stores calcium. Calcium ions are released from the sarcoplasmic reticulum during muscle contraction to trigger the interaction between actin and myosin, leading to muscle contraction. The smooth ER is responsible for the synthesis, storage, and release of calcium ions in muscle cells.Rate this question:
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- 7.
Your patient comes to your office complaining of an unusual muscle spasm problem in her gluteal region. You suspect a hypertensive muscle in that area and decide to administer a gluteal injection in the superior lateral quadrant to avoid damaging the sciatic nerve.Which of the following would you expect to find in your syringe?
- A.
Acetylcholine
- B.
Epinephrine
- C.
Dihydropyridine
- D.
Ryanodine
- E.
Calcium infused isotonic fluid
Correct Answer
C. DihydropyridineExplanation
In the t-tubule, there are dihydropyridine (DHP) receptors which help skeletal muscles contract. Applying dihydropyridine to the patient's gluteal region will help block the muscle contraction mechanism by binding to the DHP receptors, thus helping her muscle spasms.
The other 4 options would likely result in more skeletal muscle contractions, thus worsening your patient's hypertensive state.Rate this question:
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- 8.
If you applied a ryanodine receptor inhibitor to a patient, would you expect the sarcoplasmic concentrations of calcium to increase during muscle contraction efforts?For the sake of this question, assume that your RyR inhibitor blocks 100% of their target receptors. Also, ignore extracellular calcium.
- A.
Yes
- B.
No
- C.
Maybe
Correct Answer
B. NoExplanation
If a ryanodine receptor inhibitor is applied to a patient, it would block the target receptors completely. Ryanodine receptors are responsible for releasing calcium from the sarcoplasmic reticulum, which is necessary for muscle contraction. Therefore, if the inhibitor blocks these receptors, the release of calcium from the sarcoplasmic reticulum would be inhibited, resulting in decreased sarcoplasmic concentrations of calcium during muscle contraction efforts. Hence, the answer is no.Rate this question:
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- 9.
The muscle fiber type that is categorized as being relatively smaller, red due to the presence of myoglobin, and has a higher concentration of mitochondria is also known as a _____ muscle fiber.
- A.
Type I
- B.
Type II a
- C.
Type II b
- D.
White
Correct Answer
A. Type IExplanation
Type I muscle fibers, also known as slow-twitch fibers, are characterized by their relatively smaller size, red color due to the presence of myoglobin, and higher concentration of mitochondria. These fibers are specialized for aerobic activities and have a high endurance capacity. They are capable of producing ATP (energy) through oxidative metabolism, which is why they have a higher concentration of mitochondria. Type I fibers are well-suited for activities such as long-distance running or cycling.Rate this question:
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- 10.
The CT associated with skeletal muscle is necessary for mechanical transmission of the contractile force generated by the myofibers.
- A.
True
- B.
False
Correct Answer
A. TrueExplanation
The connective tissue (CT) associated with skeletal muscle plays a crucial role in transmitting the contractile force generated by the muscle fibers. It provides structural support and helps in distributing the force evenly throughout the muscle. Without the CT, the force generated by the muscle fibers would not be efficiently transmitted, leading to a decrease in mechanical function. Therefore, it is necessary for the CT to be present in order for the contractile force to be mechanically transmitted.Rate this question:
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- 11.
Muscle weakness characterized by a higher amount of satellite cell repair in muscle tissue is based on the absence of which protein?
- A.
A-actinin
- B.
Dystrophin
- C.
Desmin
- D.
Titin
Correct Answer
B. DystrophinExplanation
Duchenne muscular dystrophy (DMD) – involves a genetic mutation thatresults in a lack of dystrophin expression in striated muscle.
Skeletal muscles of DMD patients have fibers in various stages of degeneration and regeneration (due to activity of satellite cells)Rate this question:
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- 12.
Which of the following is absent in smooth muscle but found in skeletal muscle?
- A.
Actin
- B.
Tropomyosin
- C.
Troponin
- D.
Myosin
- E.
Desmin
Correct Answer
C. TroponinExplanation
Troponin is absent in smooth muscle but found in skeletal muscle. Troponin is a regulatory protein that plays a key role in muscle contraction. It binds to actin and tropomyosin, helping to regulate the interaction between actin and myosin. In skeletal muscle, troponin is necessary for the regulation of muscle contraction, while in smooth muscle, other mechanisms are involved in regulating contraction, and troponin is not present. Therefore, troponin is the correct answer as it is the only option that is absent in smooth muscle.Rate this question:
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- 13.
Which of the following blocks the actin binding site in smooth muscle?
- A.
Troponin
- B.
Calmodulin
- C.
Caveolae
- D.
Myosin light chain
Correct Answer
D. Myosin light chainExplanation
The myosin light chain blocks the actin binding site in smooth muscle. When calcium ions bind to calmodulin, it activates myosin light chain kinase, which phosphorylates the myosin light chain. This phosphorylation causes a conformational change in the myosin molecule, allowing it to bind to actin and initiate muscle contraction. Therefore, the myosin light chain plays a crucial role in regulating the interaction between actin and myosin in smooth muscle.Rate this question:
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- 14.
Your patient comes to your office complaining of pain in her abdomen due to a blunt trauma accident. With your knowledge in anatomy, you know that the GI tract is lined with smooth muscles. If you suspect damage to her smooth muscles in the GI tract, which of the following best describes the repair mechanism of the tissue located there?
- A.
Repair through satellite cells
- B.
Repair through fibroblasts
- C.
Mitosis of new cells
Correct Answer
C. Mitosis of new cellsExplanation
Smooth muscle regeneration
Damage to smooth muscle triggers mitosis of the living smooth muscle cells, which replace the damaged tissue.
If you were thinking satellite cells, just remember that they are typically used in the repair of skeletal muscle.Rate this question:
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- 15.
Skeletal muscle t-tubules:
- A.
Line up with the z-disc
- B.
Are invaginations of the sarcolemma
- C.
Have connexons
- D.
More than one of the above
Correct Answer
B. Are invaginations of the sarcolemmaExplanation
Skeletal muscle t-tubules are invaginations of the sarcolemma. This means that they are extensions of the muscle cell membrane that penetrate into the interior of the muscle fiber. The t-tubules play a crucial role in muscle contraction by allowing the action potential to quickly reach the deep regions of the muscle fiber, ensuring synchronous contraction of the entire muscle cell. The t-tubules also help in the exchange of ions and nutrients between the extracellular fluid and the muscle fiber.Rate this question:
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