BIO beast mode > Muscles > Flashcards

Muscles Flashcards

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1
Q

Q: Are skeletal muscles voluntary or involuntary?

A

A: Voluntary.

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2
Q

Q: Are skeletal muscles striated?

A

A: Yes, they are striated and have sarcomeres.

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3
Q

Q: Are skeletal muscle cells multinucleated or uninucleated?

A

A: Multinucleated.

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4
Q

Q: Are skeletal muscle fibers branching?

A

A: No, they are non-branching.

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5
Q

Q: Are cardiac muscles voluntary or involuntary?

A

A: Involuntary.

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6
Q

Q: Are cardiac muscles striated?

A

A: Yes, they are striated and have sarcomeres.

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7
Q

Q: Are cardiac muscle cells multinucleated or uninucleated?

A

A: Uninucleated.

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8
Q

Q: Are cardiac muscle fibers branching?

A

A: Yes, they are branching.

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9
Q

Q: Are smooth muscles voluntary or involuntary?

A

A: Involuntary (controlled by the autonomic nervous system).

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10
Q

Q: Are smooth muscles striated?

A

A: No, they are non-striated (no sarcomeres).

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11
Q

Q: Are smooth muscle cells multinucleated or uninucleated?

A

A: Uninucleated.

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12
Q

Q: Are smooth muscle fibers branching?

A

A: No, they are non-branching.

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13
Q

Q: What is the sarcolemma?

A

A: It is the cell membrane of a muscle cell (myocyte/muscle fiber).

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14
Q

Q: What is the sarcoplasmic reticulum?

A

A: It is the specialized endoplasmic reticulum in a muscle cell, involved in calcium storage and release.

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15
Q

Q: What is the neuromuscular junction?

A

A: The synapse between a motor neuron terminal and a muscle fiber.

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16
Q

Q: What are three terms used to describe a muscle cell?

A

A: Myocyte, muscle fiber, muscle cell.

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17
Q

Q: What is the structural hierarchy within a skeletal muscle?

A

A:

→ Muscle contains bundles of fascicles
→ each fascicle contains bundles of muscle fibers (myocytes)
→ each muscle fiber contains bundles of myofibrils
→ each myofibril contains sarcomeres (contractile units)

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18
Q

Q: What are the three types of muscle fibers?

A

A: Type I (slow oxidative), Type IIa (fast oxidative), and Type IIb (fast glycolytic).

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19
Q

Q: What are the features of Type I muscle fibers?

A

A:
• Slow-twitch, aerobic
• High in myoglobin and mitochondria
• Red in color
• Fatigue-resistant
• Rich in capillaries
• Suited for endurance and repeated actions

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20
Q

Q: What are the features of Type IIa muscle fibers?

A

A:
• Fast-twitch, uses both aerobic and anaerobic respiration
• Medium-high myoglobin and mitochondria
• Red in color
• Moderately fatigue-resistant
• Rich in capillaries
• Capable of repeated actions
• Type IIb fibers can convert to Type IIa with training

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21
Q

Q: What are the features of Type IIb muscle fibers?

A

A:
• Fast-twitch, anaerobic only
• Low in myoglobin and mitochondria
• White in color
• Not fatigue-resistant
• Low capillary density
• Suited for quick, powerful actions
• Can convert into Type IIa with training

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22
Q

Q: What is the Z-line in a sarcomere?

A

A: It marks the boundary between two sarcomeres and anchors the thin (actin) filaments.

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23
Q

Q: What is the M-line in a sarcomere?

A

A: The center of the sarcomere; it anchors the thick (myosin) filaments.

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24
Q

Q: What is the A-band in a sarcomere?

A

A: it includes the entire length of the myosin filament.

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25
Q: What is the H-zone in a sarcomere?
A: The region that contains only thick (myosin) filaments and is located in the center of the A-band.
26
Q: What is the I-band in a sarcomere?
A: The region that contains only thin (actin) filaments, spanning two adjacent sarcomeres on either side of the Z-line.
27
Q: Which part of the sarcomere shortens during muscle contraction?
A: The I-band and H-zone shrink; Z-lines are pulled toward the M-line.
28
Q: Which part of the sarcomere remains the same length during contraction?
A: The A-band stays the same, as the length of the thick filament (myosin) does not change.
29
Q: What happens to the H-zone during full muscle contraction?
A: The H-zone disappears as the actin filaments slide in and touch at the M-line.
30
Q: What is the structure of a myosin molecule in a sarcomere?
A: Myosin is a protein that forms the thick filament and consists of two polypeptide chains twisted in a helix, with two heads and two arms, forming a crossbridge.
31
Q: What are the binding sites on the myosin heads?
A: • ATP-binding site • Actin-binding site • Catalytic site (ATPase activity)
32
Q: What is the structure of actin in a sarcomere?
A: Actin is a protein that forms the thin filament and consists of two chains in a helix with active sites that bind to myosin heads.
33
Q: What is the role of tropomyosin in muscle contraction?
A: Tropomyosin blocks the myosin-binding sites on actin at rest, preventing interaction.
34
Q: What is the role of troponin in muscle contraction?
A: Troponin binds calcium ions, changes shape, and pulls tropomyosin away to expose actin’s binding site.
35
Q: What triggers troponin to move tropomyosin away from actin’s binding site?
A: Calcium ion (Ca²⁺) binding to troponin.
36
Q: What happens when calcium binds to troponin?
A: Troponin changes shape, moves tropomyosin, exposes actin’s binding site, and allows myosin to bind actin.
37
Q: What does myosin do after binding to actin?
A: Myosin pulls actin toward the M-line, causing sarcomere shortening, which leads to contraction of the myofibril, muscle fiber, fascicle, and ultimately the entire muscle.
38
Q: What is the sarcolemma?
A: The cell membrane of a muscle fiber (myocyte).
39
Q: What is the sarcoplasmic reticulum?
A: A specialized endoplasmic reticulum in muscle cells that stores and releases calcium ions (Ca²⁺).
40
Q: What are T-tubules (transverse tubules)?
A: Invaginations of the sarcolemma that allow action potentials to travel deep into the muscle fiber.
41
Q: What is the neuromuscular junction?
A: The synapse between a motor neuron and a muscle fiber.
42
Q: What is the correct order of events in skeletal muscle contraction?
A: 1. Action potential arrives at the neuromuscular junction. 2. It spreads along the sarcolemma. 3. It travels down the T-tubules. 4. It stimulates the sarcoplasmic reticulum to release Ca²⁺. 5. Calcium ions diffuse in the sarcoplasm and bind to troponin. 6. Troponin pulls tropomyosin, exposing actin’s binding site. 7. Myosin binds actin, leading to contraction (power stroke).
43
Q: What protein forms the thick filament?
A: Myosin – with two heads, two arms, and ATP/actin binding sites and the catalytic site.
44
Q: What protein forms the thin filament?
A: Actin – with binding sites for myosin crossbridges.
45
Q: What blocks the actin-myosin interaction at rest?
A: Tropomyosin, which covers actin’s binding site.
46
Q: What causes tropomyosin to move?
A: Troponin, after binding to Ca²⁺, changes shape and pulls tropomyosin.
47
Q: What is the Z-line?
A: It separates two sarcomeres and anchors thin filaments (actin).
48
Q: What is the M-line?
A: The center of the sarcomere and the middle of the thick filament (myosin).
49
Q: What is the A-band?
A: The region where actin and myosin overlap, which includes the whole length of the myosin filament.
50
Q: What is the H-zone?
A: The area with only thick filament (myosin).
51
Q: What is the I-band?
A: The region with only thin filament (actin).
52
Q: What happens to the sarcomere during muscle contraction?
A: • Z-lines move closer to the M-line • H-zone and I-band shrink • A-band stays the same • Actin slides over myosin • Myosin pulls actin toward M-line
53
Q: What happens when an action potential reaches the axon terminal of a motor neuron?
A: It causes Ca²⁺ to enter the neuron, leading to the release of acetylcholine (ACh) into the neuromuscular junction.
54
Q: What does acetylcholine do at the neuromuscular junction?
A: It binds to ligand-gated receptors on the muscle fiber, triggering an action potential in the muscle cell.
55
Q: How does the action potential reach the sarcoplasmic reticulum (SR)?
A: It spreads along the sarcolemma and travels down the T-tubules to stimulate the SR to release Ca²⁺.
56
Q: What happens after calcium is released from the SR?
A: Calcium ions diffuse through the sarcoplasm and bind to troponin, which shifts tropomyosin, exposing the myosin-binding sites on actin.
57
Q: What is the first step of the cross-bridge cycle?
A: Myosin head, in its energized state (bound to ADP + Pi), binds to actin forming a cross-bridge.
58
Q: What causes the power stroke?
A: ADP and Pi are released, and the myosin head pivots, pulling actin toward the M-line (power stroke).
59
Q: How does the myosin head detach from actin?
A: A new ATP binds to the myosin head, causing it to release actin.
60
Q: How is myosin reactivated for the next cycle?
A: Myosin hydrolyzes ATP → ADP + Pi, returning to its cocked (energized) position.
61
Q: When does the cross-bridge cycle stop?
A: When Ca²⁺ is pumped back into the SR, troponin loses Ca²⁺, and tropomyosin blocks actin again → muscle relaxes.
62
Q: What are the 5 steps of the cross-bridge cycle in correct order?
A: 1. Energized myosin (with ADP + Pi) binds to actin and Pi is released making the bond stronger. 2. ADP is released → power stroke occurs. 3. ATP binds to myosin → detachment from actin. 4. ATP is hydrolyzed → myosin re-cocks to energized state. 5. Pi is released and myosin binds to actin. Note: Cycle repeats if calcium is present; ends when calcium is reabsorbed into SR.
63
Q: What is a “cross-bridge” in muscle contraction?
A: A cross-bridge is the temporary connection between myosin heads and actin filaments formed during contraction.
64
Q: What triggers the power stroke in the cross-bridge cycle?
A: The release of ADP and Pi from the myosin head after it binds to actin.
65
Q: What returns myosin to its energized (cocked) state?
A: ATP hydrolysis (ATP → ADP + Pi).
66
Q: What is the end plate potential?
A: A local depolarization caused by Na⁺ influx when ACh binds to ligand-gated Na⁺ channels. If threshold (–55 mV) is reached, it triggers an action potential.
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