Vander's Physiology 9 TQR (multiple choices)

Which is a FALSE statement about skeletal muscle structure? a. A myofibril is composed of multiple muscle fibers. b. Most skeletal muscles attach to bones by connective-tissue tendons c. Each end of a thick filament is surrounded by six thin filaments d. A cross-bridge is a portion of the myosin molecule e. Thin filaments contain actin, tropomyosin, and troponin

CORRECT ANSWER: A A single muscle fiber is made up a collection of myofibrils. These myofibrils have additional components that allow contractions of the muscle B is eliminated: tendons are bundles of collagen fibers that attach skeletal muscles to bones. These tendons are connective tissue. C is eliminated: In a single myofibril there is a thick filament that is surrounded by six thin filaments. Surrounding the thin filaments are three thick filaments. . D is eliminated: the cross-bridge is the portion of the myosin molecule that connects the thick and thin filaments during contraction E is eliminated because it is true.

The function of myosin light-chain kinase in smooth muscle is to: a. bind to calcium ions to initiate excitation-contraction coupling. b. phosphorylate cross-bridges, thus driving them to bind with the thin filament. c. Split ATP to provide the energy for the power stroke of the cross-bridge cycle d. dephosphorylate myosin light chains of the cross-bridge, thus relaxing the muscle e. pump Ca2+ from the cytosol back into the sarcoplasmic reticulum.

CORRECT ANSWER: B Myosin light-chain kinase is used to phosphorylate myosin light chains of myosin. During this process, Ca2+-Calmodulin complex binds to the kinase, and then uses ATP to phosphorylate myosin, which then activates the binding and cycling of the cross-bridges to actin. A is eliminated: Ca2+ does not control the cycling of the cross-bridge in smooth muscle, because the necessary binding protein, troponin, for excitation-contraction coupling is not present. C is eliminated: Myosin light chain kinase uses ATP during the phosphorylation process of the globular head of myosin, not splitting ATP to provide energy to the cross-bridge cycle. D is eliminated: Myosin light-chain phosphatase is responsible for the dephosphorylation of the cross-bridge, which allows the muscle to relax E is eliminated: When Ca2+ is pumped back into the sarcoplasmic reticulum, dephosphorylation is occurring in the muscle. This is because of the high level of Ca2+ in the cytosol, and the enzyme activity of myosin light-chain phosphatase is increased.

What prevents a drop in muscle fiber ATP concentration during the first few seconds o intense contraction? a. Because cross-bridges are pre-energized, ATP is not needed until several cross-bridge cycles have been completed b. ADP is rapidly converted back to ATP by creatine phosphate c. Glucose is metabolized in glycolysis, producing large quantities of ATP d. The mitochondria immediately begin oxidative phosphorylation. e. Fatty acids are rapidly converted to ATP by oxidative glycolysis.

CORRECT ANSWER: B during the beginning of contraction/exercise, ATP concentration will fall because of its breakdown by myosin into ADP. However, mass action favors ATP over creatine phosphate, so there is an energy transfer, in the form of high-energy phosphate, to ATP. This leaves a small difference in ATP concentration during the beginning of exercise. A is eliminated: Cross bridges are not pre-energized. They require the energy from AtP hydrolysis dor any movement. C is eliminated: Glycolysis will not contribute ATP during contraction unless the intensity causes an ATP breakdown rate of higher than 70%. This process will not contribute ATP to the muscle fiber during the initial start of contraction. D is eliminated: Oxidative phosphorylation will form ATP during moderate levels of activity, and is typically seen during the first ten minutes of exercise. The mitochondria will not begin this process immediately after starting exercise, because it is a slower, multienzyme pathway. E is eliminated: Fatty acids will be converted to ATP during the later stages of contraction of exercise, specifically in oxidative phosphorylation.

When a skeletal muscle fiber undergoes a concentric isotonic contraction, a. M lines remain the same distance apart. b. Z lines move closer to the ends of the A band. c. A bands become shorter. d. I bands become wider. e. M lines move closer to the end of the A band.

CORRECT ANSWER: B A concentric isotonic contraction causes the skeletal muscle to shorten with each contraction. The sarcomere is shortened because the thick and thin filaments overlap, allowing the Z lines to move closer to the A bands. During a concentric contraction, the M lines will get closer together, because of the overlapping of the thick and thin filaments, which shortens the sarcomeres. The A band will remain the same length, because there is no change in the length of the thick or thin filaments. The only change is that the filaments overlap. Also the I bands become shorter because of the overlap. The M line will not move closer the ends of the A band, because the M line is centered in the middle of the A band.

Why is the latent period longer during an isotonic twitch of a skeletal muscle fiber than it is during an isometric twitch? a. Excitation-contraction coupling is slower during an isotonic twitch b. Action potentials propagate more slowly when the fiber is shortening, so extra time is required to activate the entire fiber c. In addition to the time for excitation-contraction coupling, it takes extra time for enough cross-bridges to attach to make the tension in the muscle fiber greater than the load. d. Fatigue sets in much more quickly during isotonic contractions, and when muscles are fatigued the cross-bridges move much more slowly. e. The latent period is longer because isotonic twitches only occur in slow (type I) muscle fibers.

CORRECT ANSWER: C During an isometric twitch, the tension rises after the excitation-contraction completes and the initial cross bridge is attached. This means the latent period is only affected by the excitation-contraction delay. (Isotonic twitch has a longer latent period because there has to be enough cross-bridges attached before a load can be moved. The latent period is affected by the excitation-contraction coupling and the time needed for the additional attachments of cross-bridges. A is eliminated: The length of time necessary for excitation-contraction coupling in an isotonic and and isometric twitch is the same. B is eliminated: When the fiber is shortened in an isotonic twitch, the additional time is affected by the need for additional cross-bridge attachment to lift a load, not the propagation of action potentials. D is eliminated: During an isotonic contraction, fatigue does not affect the time of the latent period. The cross-bridges do not move slowly in this contraction than an isometric, it is the need for additional cross-bridges connections that affects the time of the latents period. E is eliminated: The latent period in an isometric twitch is affected by the increased need for cross-bridge attachments. Furthermore, when describing a fiber as slow vs. fast, it refers to the rate of cross bridge cycling, but not the force produced by these cross bridges.

Which is FALSE regarding the structure of smooth muscle? a. The thin filament does not include the regulatory protein troponin. b. The thick and thin filaments are not organized in sarcomeres. c. Thick filaments are anchored to dense bodies instead of Z lines. d. The cells have a single nucleus. e. Single-unit smooth muscles have gap junctions connecting individual cells.

CORRECT ANSWER: C For a smooth muscel cell, a dense body is similar to a Z line in function. The thin filaments connect to the dense body, not the thick filaments. A is eliminated: In the smooth muscle, troponin is absent from the thin filament. However trypomyosin is still seen in the muscle type. B is eliminated: Smooth muscle fibers do not have the same organizational structure as skeletal muscle. The thick and thin filaments are not organized in sarcomeres and have no consistent alignment. D is eliminated: Smooth muscle cells are not multi-nucleated, since there is only one nucleus n this muscle type, the cells can divide throughout the lifetime of the host body. E is eliminated: Gap junctions are what join each individual smooth muscle fiber into the continuous sheet of smooth muscle.

Single unit smooth muscle differs from multiunit smooth muscle because: a. single-unit muscle contraction speed is slow, and multiunit is fast. b. single-unit muscle has T-tubules, and multiunit muscle does not. c. single-unit muscles are not innervated by autonomic nerves. d. single-unit muscle contracts when stretched, whereas multiunit muscle does not. e. single-unit muscle does not produce action potentials spontaneously, but multiunit muscle does

CORRECT ANSWER: D A difference between single-unit and multiunit smooth muscle involves the contraction of the muscle types. In a single-unit smooth muscle, stretching a muscle can cause a contraction response. As the muscle stretches, mechanically gated ion channels are opened, which causes depolarization. This mechanism allows for calcium to enter and lead to contraction. Stretching does not lead to contraction in a multiunit smooth muscle. A is eliminated: The speed of contraction does not differentiate whether smooth muscle is single-unit or multiunit B is eliminated: Smooth muscle does not have T-tubules present C is eliminated: Both single-unit and multiunit smooth muscles are innervated by the autonomic nervous system E is eliminated: Action potentials in single-unit smooth muscles do occur spontaneously. However, in most multiunit smooth muscles, action potential does not occur.

During excitation-contraction coupling in a skeletal muscle fiber: a. The Ca2+-ATPase pumps Ca2+ into the T-tubule. b. Action potentials propagate along the membrane of the sarcoplasmic reticulum. c. Ca2+ floods the cytosol through the dihydropyridine (DHP) receptorsþ d. DHP receptors triggers the opening of terminal cisternae ryanodine recrptor CA2+ channels e. acetylcholine opens the DHP receptor channel.

CORRECT ANSWER: D An excitation-concentration coupling leads to the contraction of a skeletal muscle fiber. In a relaxed state, there is a higher concentration of Ca2+ in the sarcoplasmic reticulum. Located within the sarcoplasmic reticulum membrane are ryanodine recptors that are linked to dihydropyridine DHP receptors. These DHP receptors receptors are voltage-sensitive Ca2+ channels. A an action potential depolarizes the T-tubule, these receptors ae able to change conformation. This, in turn, opens the ryanodine receptors, which are located on the lateral sacs of the sarcoplasmic reticulum. For the duration of muscle contraction, Ca2+ diffuses from the sarcoplasmic reticulum into the cytosol. As a contraction of a skeletal muscle fiber begins, the action potential propagates into the T-tubule, not the sarcoplasmic reticulum. For the remainder of the contraction of the muscle, there is a higher concentration of Ca2+ located in the cytosol of the cell. As the contraction ends, the Ca2+- ATPases pumps Ca2+ into the sarcoplasmic reticulum. Since Ca2+ is not concentrated in the T-tubule throughout this process (option a is eliminated) Ca2+ is released from the lateral sacs into the cytosol not through the dihydropidine receptors When acetylcholine is released, t binds to nicotinic receptors, when then opens an ion channel that allows Na+ and + to pass.

Which correctly characterizes a "fast-oxidative" type of skeletal muscle fiber? a. few mitochondria and high glycogen content. b. low myosin ATPase rate and few surrounding capillaries c. low glycolytic enzyme activity and intermediate contraction velocity. d. high myoglobin content and intermediate glycolytic enzyme activity e.. small fiber diameter and fast onset of fatigue

CORRECT ANSWER: D A fast-oxidative-glycolytic fiber has high ATPase activity and a high oxidative capacity, as well as an intermediate ability to use the glycolytic pathways in the generation of ATP. It is described as a red muscle, meaning it has a high myoglobin content. It also has an intermediate ability to resist fatigue, because it uses oxidative and glycolytic pathways for ATP generation. A is eliminated; A skeletal muscle fiber with a slow number of mitochondria and high glycogen content is a fast-glycolytic fiber. B is eliminated: The skeletal muscle fiber with low myosin- ATPase rate and a low number of capillaries is a slow-oxidative fiber. C is eliminated: The skeletal muscle with low glycolytic content is a slow-oxidative fiber. There are not any fibers with an intermediate contraction velocity. They can either be fast or slow. E is eliminated: The skeletal muscle fiber with a small fiber diameter is a slow-oxidative fiber, while the type with a fast onset of fatigue is the fast-glycolytic fiber.

Which is correct regarding a skeletal muscle sarcomere? a. M lines are found in the center of the I band. b. The I band is the space between one Z line and the next. c. the H zones is the region where thick and thin filaments overlap. d. Z lines are found in the center of the A band. e. The witdth of the A band is equal to the length of a thick filament.

CORRECT ANSWER: E The A band is made of wide, dark stripes of striated muscle, also known as thick filaments, which lie in the center of the sarcomere segment. When these thick filaments are arranged parallel to one another within myofibrils, their length is equal to the width of the A band. The M line is located in the middle of the H zone, and connects adjacent thick filaments in the center of the sarcomere. The H zone is the are within the A band that is the space where the two ends of thin filaments are opposing one another. The I band is found at the end of an A band and connects to the end of an adjacent A band of two sarcomeres The z line is located in the center of the I band and is considered the outer limit of a sarcomere.