Muscular System AP Biology Post Quiz

1. All of the following are involved in the contraction of a muscle EXCEPT:

Actin

CAMP

Myosin

Tropomyosin

Troponin

cAMP, or cyclic adenosine monophosphate, is not directly involved in the contraction of a muscle. Instead, it serves as a secondary messenger in intracellular signaling pathways. Actin, myosin, tropomyosin, and troponin are all key components of the muscle contraction process. Actin and myosin interact to generate the force for muscle contraction, while tropomyosin and troponin regulate this interaction by controlling the exposure of binding sites on actin.

Explanation

cAMP, or cyclic adenosine monophosphate, is not directly involved in the contraction of a muscle. Instead, it serves as a secondary messenger in intracellular signaling pathways. Actin, myosin, tropomyosin, and troponin are all key components of the muscle contraction process. Actin and myosin interact to generate the force for muscle contraction, while tropomyosin and troponin regulate this interaction by controlling the exposure of binding sites on actin.

2. Which type of muscle is responsible for peristalsis along the digestive tract?

Voluntary

Smooth

Skeletal

Striated

Cardiac

Smooth muscle is responsible for peristalsis along the digestive tract. Peristalsis is the coordinated contraction and relaxation of muscles that helps move food through the digestive system. Smooth muscle is found in the walls of the digestive organs and is involuntary, meaning it is not under conscious control. This type of muscle is able to contract and relax in a rhythmic pattern, allowing for the movement of food through the digestive tract.

Explanation

Smooth muscle is responsible for peristalsis along the digestive tract. Peristalsis is the coordinated contraction and relaxation of muscles that helps move food through the digestive system. Smooth muscle is found in the walls of the digestive organs and is involuntary, meaning it is not under conscious control. This type of muscle is able to contract and relax in a rhythmic pattern, allowing for the movement of food through the digestive tract.

3. During muscle contraction, the ion that leaks out of the sarcoplasmic reticulum and induces myofibrils to contract is

Cl-

K+

Mg2+

Ca2+

Na+

During muscle contraction, the ion that leaks out of the sarcoplasmic reticulum and induces myofibrils to contract is Ca2+. Calcium ions bind to the regulatory protein troponin, causing a conformational change that allows the myosin heads to interact with the actin filaments. This interaction leads to the sliding of the actin and myosin filaments, resulting in muscle contraction.

Explanation

During muscle contraction, the ion that leaks out of the sarcoplasmic reticulum and induces myofibrils to contract is Ca2+. Calcium ions bind to the regulatory protein troponin, causing a conformational change that allows the myosin heads to interact with the actin filaments. This interaction leads to the sliding of the actin and myosin filaments, resulting in muscle contraction.

4. What is the role of calcium in muscle contractions?

To bind with troponin, changing its shape so that the actin filament is exposed

To break the cross-bridges as a cofactor in the hydrolysis of ATP

To transmit the action potential across the neuromuscular junction

To spread the action potential through the T tubules

To reestablish the polarization of the plasma's membrane following an action potential

Calcium plays a crucial role in muscle contractions by binding with troponin, a protein found on the actin filament. This binding causes a conformational change in troponin, which then moves tropomyosin away from the myosin-binding sites on actin. This exposure of the actin filament allows myosin heads to bind with actin and initiate the contraction process. Therefore, calcium's role in muscle contractions is to bind with troponin and facilitate the interaction between actin and myosin.

Explanation

Calcium plays a crucial role in muscle contractions by binding with troponin, a protein found on the actin filament. This binding causes a conformational change in troponin, which then moves tropomyosin away from the myosin-binding sites on actin. This exposure of the actin filament allows myosin heads to bind with actin and initiate the contraction process. Therefore, calcium's role in muscle contractions is to bind with troponin and facilitate the interaction between actin and myosin.

5. Muscle cells are stimulated by neurotransmitters released from the tips of:

T tubules

Motor cell axons

Motor cell dendrites

Sensory cell dendrites

Sensory cell axons

Muscle cells are stimulated by neurotransmitters released from the tips of motor cell axons. Motor cell axons are responsible for transmitting signals from the central nervous system to the muscles. When a motor neuron is activated, it releases neurotransmitters at the neuromuscular junction, which then bind to receptors on the muscle cell membrane. This binding triggers a series of events that ultimately result in muscle contraction. Therefore, the neurotransmitters released from the tips of motor cell axons are essential for initiating muscle cell activation and contraction.

Explanation

Muscle cells are stimulated by neurotransmitters released from the tips of motor cell axons. Motor cell axons are responsible for transmitting signals from the central nervous system to the muscles. When a motor neuron is activated, it releases neurotransmitters at the neuromuscular junction, which then bind to receptors on the muscle cell membrane. This binding triggers a series of events that ultimately result in muscle contraction. Therefore, the neurotransmitters released from the tips of motor cell axons are essential for initiating muscle cell activation and contraction.

6. 1. Tropomyosin shifts and unblocks the cross-bridge binding sites. 2. Calcium is released and binds to troponin. 3. Transverse tubules depolarize the sarcoplasmic reticulum. 4. The thin filaments are ratcheted across the thick filaments by the heads of the myosin molecules and ATP. 5. An action potential in a motor neuron causes the axon to release acetylcholine, which depolarizes the muscle cell membrane. For the events listed above, which of the following is the correct sequence for their occurrence during the excitation and contraction of a muscle cell?

1, 2, 3, 4, 5

2, 3, 4, 1, 5

2, 1, 3, 5, 4

5, 3, 2, 1, 4

5, 3, 1, 2, 4

The correct sequence for the events during the excitation and contraction of a muscle cell is as follows:
1. An action potential in a motor neuron causes the axon to release acetylcholine, which depolarizes the muscle cell membrane. (Event 5)
2. Transverse tubules depolarize the sarcoplasmic reticulum. (Event 3)
3. Calcium is released and binds to troponin. (Event 2)
4. Tropomyosin shifts and unblocks the cross-bridge binding sites. (Event 1)
5. The thin filaments are ratcheted across the thick filaments by the heads of the myosin molecules and ATP. (Event 4)

Explanation

The correct sequence for the events during the excitation and contraction of a muscle cell is as follows:
1. An action potential in a motor neuron causes the axon to release acetylcholine, which depolarizes the muscle cell membrane. (Event 5)
2. Transverse tubules depolarize the sarcoplasmic reticulum. (Event 3)
3. Calcium is released and binds to troponin. (Event 2)
4. Tropomyosin shifts and unblocks the cross-bridge binding sites. (Event 1)
5. The thin filaments are ratcheted across the thick filaments by the heads of the myosin molecules and ATP. (Event 4)

7. When an organism dies, its muscles remain in a contracted state termed rigor mortis for a brief period of time. Which of the following most directly contributes to this phenomenon?

No ATP to break bonds between the actin and myosin

No oxygen supplied to muscle

No energy for the synthesis of actin and myosin

No ATP to move cross-bridges

No calcium to bind to troponin

Rigor mortis occurs when the muscles of a dead organism become stiff and locked in a contracted state. This phenomenon is caused by a lack of ATP (adenosine triphosphate), which is required for muscle relaxation. ATP is needed to break the bonds between actin and myosin, the proteins responsible for muscle contraction. Without ATP, the actin and myosin remain bound together, resulting in the rigidity of muscles observed during rigor mortis.

Explanation

Rigor mortis occurs when the muscles of a dead organism become stiff and locked in a contracted state. This phenomenon is caused by a lack of ATP (adenosine triphosphate), which is required for muscle relaxation. ATP is needed to break the bonds between actin and myosin, the proteins responsible for muscle contraction. Without ATP, the actin and myosin remain bound together, resulting in the rigidity of muscles observed during rigor mortis.

8. Which of the following does not form part of the actin filament of a muscle cell?

Tropomyosin

Calcium-binding site

Troponin

Myosin

Thin filament

Myosin is not a part of the actin filament of a muscle cell. Myosin is a protein that forms the thick filament in muscle cells and is responsible for the contraction of muscles. Actin filaments, on the other hand, are composed of the protein actin and are involved in muscle contraction by interacting with myosin. Therefore, myosin is not a part of the actin filament in a muscle cell.

Explanation

Myosin is not a part of the actin filament of a muscle cell. Myosin is a protein that forms the thick filament in muscle cells and is responsible for the contraction of muscles. Actin filaments, on the other hand, are composed of the protein actin and are involved in muscle contraction by interacting with myosin. Therefore, myosin is not a part of the actin filament in a muscle cell.

9. Which of the following is the last step leading up to muscle contraction that occurs just before a myofibril contracts

Tropomyosin exposes binding sites on actin

ATP binds to myosin

Sarcoplasmic reticulum releases calcium ions

ATP is converted to ADP and Pi

Action potential travels through T-tubules

Tropomyosin is a protein that covers the binding sites on actin, preventing myosin from binding to actin. When tropomyosin exposes the binding sites on actin, it allows myosin to bind to actin, which is an essential step for muscle contraction to occur. This allows the sliding filament mechanism to take place, where myosin pulls on actin, causing the muscle to contract. Therefore, tropomyosin exposing the binding sites on actin is the last step leading up to muscle contraction before a myofibril contracts.

Explanation

Tropomyosin is a protein that covers the binding sites on actin, preventing myosin from binding to actin. When tropomyosin exposes the binding sites on actin, it allows myosin to bind to actin, which is an essential step for muscle contraction to occur. This allows the sliding filament mechanism to take place, where myosin pulls on actin, causing the muscle to contract. Therefore, tropomyosin exposing the binding sites on actin is the last step leading up to muscle contraction before a myofibril contracts.