Skeletal Muscle Questions Quiz! Trivia

Free intracellular calcium

Hypocalcemia is a condition characterized by low levels of calcium in the blood. Calcium plays a crucial role in muscle function, and low levels of calcium can lead to muscle spasms and contractions. Therefore, hypocalcemia can cause spasms. On the other hand, hypercalcemia refers to high levels of calcium in the blood, which is not associated with muscle spasms.

Troponin and tropomyosin are proteins that are involved in regulating muscle contraction. They form a complex that wraps around the actin filament in muscle cells. This complex plays a crucial role in controlling the interaction between actin and myosin during muscle contraction. When calcium ions bind to troponin, it causes a conformational change in tropomyosin, exposing the binding sites on actin for myosin. This allows the sliding of actin and myosin filaments, leading to muscle contraction. Therefore, the correct answer is Actin.

Extracellular calcium can indeed block Na channels, which are responsible for generating action potentials. When these channels are blocked, the nerve cells are unable to transmit signals properly, leading to a decrease or complete loss of muscle tone, known as flaccid paralysis. Therefore, the statement is true.

ATP binding does indeed break cross bridges in muscle contraction. When a muscle contracts, myosin heads form cross bridges with actin filaments. This cross bridge allows myosin to pull the actin filaments, resulting in muscle contraction. However, for the cross bridge to detach and allow the muscle to relax, ATP must bind to the myosin head. This binding causes a conformational change in the myosin head, breaking the cross bridge and allowing the muscle to relax. Therefore, the correct answer is yes.

The sarcomere is the basic functional unit of a muscle fiber. It is composed of various structures, including I bands, A bands, Z lines, and H zones. The Z lines mark the boundaries of the sarcomere and separate one sarcomere from the next. Therefore, the distance between Z lines determines the length of the sarcomere.

In the relaxed state, tropomyosin covers the binding site for actin. This means that actin cannot bind to other molecules such as myosin, preventing muscle contraction. When the muscle is stimulated to contract, calcium ions are released, which bind to troponin. This causes a conformational change in tropomyosin, exposing the binding site on actin. Myosin can then bind to actin, initiating the sliding of actin and myosin filaments and muscle contraction.

Intrafusal fibers are responsible for regulating sensors and are innervated by gamma motor neurons. These fibers are found within muscle spindles, which are sensory organs that detect changes in muscle length and tension. When the muscle is stretched, the intrafusal fibers relay this information to the central nervous system through sensory neurons. The gamma motor neurons then regulate the sensitivity of the muscle spindles by adjusting the tension in the intrafusal fibers. This allows for precise control of muscle contraction and helps maintain muscle tone.

The A band refers to the entire length of the myosin filaments in a muscle sarcomere. It includes both the overlapping actin and myosin filaments, giving it a dark appearance under a microscope. The A band is responsible for muscle contraction as the myosin filaments slide over the actin filaments during muscle contraction.

The correct answer is the transport of calcium back into the SR. This is because during muscle contraction, calcium ions are released from the sarcoplasmic reticulum (SR) into the muscle cell, which triggers the contraction. Once the contraction is complete, the calcium ions need to be removed from the muscle cell in order for it to relax. This is done by actively transporting the calcium ions back into the SR, which allows the muscle to return to its resting state and terminate the contraction.

Type I fibers are known as slow-twitch fibers and are responsible for endurance activities. These fibers have a high capacity for aerobic metabolism and are fatigue-resistant, making them ideal for activities that require prolonged contractions, such as long-distance running or cycling. Type II fibers, on the other hand, are fast-twitch fibers that are used for explosive movements and have a higher capacity for anaerobic metabolism. Therefore, the correct answer is type I, as these fibers are specifically designed for endurance activities.

Active tension refers to the force generated by the contraction of muscle fibers. This force is produced as a result of the interaction between actin and myosin filaments in the muscle, which occurs when cross-bridges are formed and broken. These cross-bridges allow the muscle fibers to contract and generate force. Therefore, active tension is the correct answer as it accurately describes the force generated by the muscle during contraction.

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Holding a heavy load requires the use of muscles to maintain stability and support the weight. This requires the activation of a few muscle groups and can be sustained for a longer period of time. On the other hand, repetitive drumming involves continuous and rapid muscle contractions, requiring more energy expenditure. Therefore, holding a heavy load uses less energy compared to repetitive drumming.

The best measurement of preload is sarcomere length. Preload refers to the initial stretching of the cardiac muscle fibers before contraction. Sarcomere length is a direct indicator of the degree of stretch on the cardiac muscle fibers, and it determines the force generated during contraction. Therefore, measuring sarcomere length provides the most accurate assessment of preload, allowing for a better understanding of cardiac function.

Extrafusal fibers are skeletal muscle fibers that are innervated by alpha motor neurons and are responsible for producing a force of contraction. These fibers are responsible for generating the actual movement and force in skeletal muscles. In contrast, intrafusal fibers are specialized muscle fibers found within muscle spindles that act as sensors for muscle length and tension. Therefore, the correct answer is extrafusal fibers.

Hypercalcemia is a condition characterized by high levels of calcium in the blood. Excess calcium can disrupt the normal functioning of the nervous system, leading to muscle weakness and flaccid paralysis. This occurs because high levels of calcium interfere with the release of neurotransmitters, impairing the communication between nerve cells and muscles. As a result, the muscles become weak and lose their ability to contract properly, causing flaccid paralysis.

The I band is the correct answer because it represents the distance from one part of a sarcomere to the same part of the next sarcomere. It is a light band that contains only thin filaments and is located between two A bands. The I band shortens during muscle contraction, allowing the thin filaments to slide over the thick filaments.

Sarcomeres are the basic functional unit for skeletal and cardiac muscles. Skeletal muscles are responsible for voluntary movements, while cardiac muscles are found in the heart and are responsible for involuntary contractions. Smooth muscles, on the other hand, do not contain sarcomeres and are found in organs like the stomach and blood vessels. Therefore, the correct answer is skeletal and cardiac.

The mechanism that provides ATP for contraction involves direct phosphorylation, glucose, and oxidation of fatty acids. Direct phosphorylation refers to the immediate transfer of a phosphate group from creatine phosphate to ADP, forming ATP. Glucose is another source of ATP, as it can be broken down through glycolysis to produce ATP. Lastly, the oxidation of fatty acids can also generate ATP through the process of beta-oxidation. These three mechanisms contribute to the production of ATP, which is essential for muscle contraction.

The activity of myosin ATPase limits the velocity. Myosin ATPase is an enzyme that hydrolyzes ATP to provide energy for muscle contraction. The rate at which myosin ATPase can hydrolyze ATP determines the speed at which the muscle can contract and therefore limits the velocity of muscle contraction.

Myosin is considered as being structural because it forms the thick filaments in muscle fibers, providing stability and support to the muscle structure. It is also considered as being mechanical because it is responsible for generating force and movement by interacting with actin filaments during muscle contraction. Additionally, myosin is considered as being an enzyme because it has ATPase activity, which allows it to hydrolyze ATP to provide the energy needed for muscle contraction.

During an isotonic contraction, there is no change in the force exerted by the muscle. This means that the force remains constant throughout the contraction. Additionally, the tension in the muscle does not increase, meaning that the level of tension remains the same. However, the length of the muscle decreases during an isotonic contraction. This occurs as the muscle fibers actively shorten, resulting in a reduction in the overall length of the muscle. Therefore, the correct answers for isotonic contraction are: no change of force, tension does not increase, and length decreases.

The given answer includes four different ways to regulate force: preload, afterload, frequency, and recruitment. Preload refers to the amount of tension in the muscle fibers before contraction, while afterload refers to the resistance the muscle must overcome to contract. Frequency refers to the rate at which muscle contractions occur, and recruitment refers to the activation of additional muscle fibers to increase force production. These four factors play a crucial role in regulating the force generated by muscles during various activities.

Active force in muscle contraction is generated when calcium ions are released from the sarcoplasmic reticulum (SR) into the muscle fiber. This release of calcium allows the binding of calcium to troponin, which initiates the sliding of actin and myosin filaments, resulting in muscle contraction. Therefore, both the presence of a calcium pulse and the release of calcium from the SR are required for active force generation. The transport of calcium back into the SR and the extracellular fluid calcium are not directly involved in the generation of active force.