A&P Chapter 9

The response of a motor unit to a single action potential of its motor neuron is called ________. A. wave summation B. a muscle twitch C. a tetanic contraction D.recruitment

A motor unit's response to a single, brief threshold stimulus (a single action potential) is a muscle twitch.

Cross bridge formation between myosin heads and actin molecules is caused by the elevation of calcium ion concentration in the cytosol. During rigor mortis, this elevation of calcium ion concentration in the cytosol is permanent because ________. A. mitochondria stop producing ATP molecules required by the sarcoplasmic reticulum's calcium ion pumps B. troponin molecules bind irreversibly to calcium ions to prevent them from being removed from the cytosol C. tropomyosin molecules bind irreversibly to calcium ions to prevent them from being removed from the cytosol D. acetylcholine continues to stimulate the release of calcium ions from the sarcoplasmic reticulum

A pump is considered an active transport process. Active transport moves molecules against their concentration gradient, which requires energy in the form of ATP.

Synaptic vesicles at the neuromuscular junction contain __________. A. ACh receptors B. synaptic potentials C. D. cal acetylcholine cium

Acetylcholine (ACh) is the neurotransmitter contained in synaptic vesicles at the neuromuscular junction. ACh allows a motor neuron to stimulate the sarcolemma of a skeletal muscle fiber.

What specific neurotransmitter is released from the axonal terminus as shown in A? A.myosin B.calcium C.acetylcholine D.actin

Acetylcholine is the neurotransmitter used exclusively at the neuromuscular junctions of skeletal muscle.

How is acetylcholine (ACh) removed from the synaptic cleft? A. acetylcholinesterase (AChE; an enzyme) only B. acetylcholinesterase (AChE; an enzyme) and endocytosis into the muscle fiber C. simple diffusion away from the synaptic cleft and acetylcholinesterase (AChE; an enzyme) D. simple diffusion away from the synaptic cleft and endocytosis into the muscle fiber

Acetylcholinesterase breaks down acetylcholine in the synaptic cleft.

What is the primary mechanism by which ACh is cleared from the synaptic cleft? A. broken down by acetylcholinesterase B. reuptake into the synaptic terminal C. endocytosis by synaptic vesicles D. diffusion away from the synaptic cleft

Acetylcholinesterase breaks down acetylcholine in the synaptic cleft. Inhibition of acetylcholinesterase, as some poisons can do, causes repeated muscle action potentials and near-constant muscle contraction.

What would happen if acetylcholine was not removed from the synaptic cleft? A. The acetylcholine receptors would not open. B. Voltage-gated Ca2+ channels would remain open. C. Multiple action potentials would occur in the motor neuron. D. Multiple action potentials would occur in the muscle fiber.

Action potentials will not cease until acetylcholine is removed from the synaptic cleft. Therefore, the constant presence of acetylcholine would cause multiple muscle action potentials and near-constant muscle contraction.

Isometric contraction leads to movement of a load. A.True B.False C. D.

An isometric contraction generates tension (force), but not enough to move the load. Overall muscle length does not change during iso(same) -metric(length) contractions. In contrast, isotonic contractions result in movement of the load.

Which statement accurately describes the event indicated by B? A. Diffusion of acetylcholine into the muscle fiber triggers the diffusion of Ca2+ out of the muscle fiber. B. Diffusion of Ca2+ into the muscle fiber triggers the diffusion of acetylcholine out of the muscle fiber. C. Binding of acetylcholine to a receptor triggers the opening of an ion channel. D. Diffusion of acetylcholine into the muscle fiber triggers the opening of an ion channel.

Binding of acetylcholine to its receptor opens chemically (ligand) gated ion channels that allow Na+ and K+ to diffuse across the sarcolemma.

The protein troponin is shown in this figure to be bound to which substance? A. sodium ion B. calcium ion C.myosin D.acetycholine

Binding of calcium by troponin (B) removes the blocking action of tropomyosin along the thin myofilament. This allows myosin to bind to actin and form the cross bridge illustrated in this figure.

What most directly causes synaptic vesicles to release acetylcholine into the synaptic cleft? A. an action potential arriving at the axon terminal B. sodium entering the muscle fiber C. depolarization of the sarcolemma D. calcium entering the axon terminal

Calcium entry causes synaptic vesicles to release acetylcholine into the synaptic cleft. Each synaptic vesicle contains thousands of acetylcholine molecules.

Cardiac muscle makes most of its ATP via anaerobic pathways. A.False B. True C. D.

Cardiac muscle generates most of its ATP via aerobic pathways (cellular respiration). The anaerobic pathways, namely glycolysis, produce lactic acid, a major cause of fatigue. Cardiac muscle cannot afford to fatigue, it must continue to contract with no more than a fraction of a second of rest between contractions for your entire life.

Acetylcholine receptors are best characterized as what type of channel? A. chemically gated Ca2+ channels B. voltage-gated Na+-K+ channels C. chemically gated Na+-K+ channels D. voltage-gated Ca2+ channels

Chemically gated ion channels open due to the binding of a neurotransmitter, such as acetylcholine. Chemically gated Na+-K+ channels allow the diffusion of Na+ into the muscle fiber and K+ out of the muscle fiber

Which of the following is CORRECTLY paired? A. smooth muscle: striated B. cardiac muscle: nonstriated C. skeletal muscle: voluntary control D. cardiac muscle: voluntary control

Correct; skeletal muscle is under voluntary control.

A muscle that is lengthening while it produces tension is performing a(an) ________ contraction. A. isometric B.maximal C.concentric D. eccentric

During isotonic, eccentric contractions muscle lengthens as is generates tension, but not enough force to overcome the load. We use eccentric contractions to lower objects (such as lowering a book from the shelf, or lowering the barbell during a bench press).

The distance between Z discs ________ during muscle contraction. A.increases B.decreases C. decreases and then increases D. stays the same

During muscle contraction, the distance between Z discs decreases as the thin myofilaments slide across thick myofilaments, toward the M line in the center of each sarcomere. As the sarcomeres shorten, the myofibrils and, thus the myofibers shorten (contract).

Which muscle characteristic describes the ability of muscle to respond to a stimulus? A. excitability B.extensibility C.elasticity D.contractility

Excitability, also termed responsiveness, is the ability to receive and respond to a stimulus, For example, skeletal muscle contracts in response to receiving chemical stimulation by a neurotransmitter called acetylcholine (ACh).

Excitation-contraction coupling is a series of events that occur after the events of the neuromuscular junction have transpired. The term excitation refers to which step in the process? A. Excitation, in this case, refers to the propagation of action potentials along the sarcolemma. B. Excitation refers to the release of calcium ions from the sarcoplasmic reticulum. C. Excitation refers to the shape change that occurs in voltage-sensitive proteins in the sarcolemma. D. Excitation refers to the propagation of action potentials along the axon of a motor neuron.

Excitation, in this case, refers to the propagation of action potentials along the sarcolemma. Yes! These action potentials set off a series of events that lead to a contraction.

In a bedridden patient recovering from a badly fractured femur, disuse atrophy in the thigh muscles is caused by _________. A. decreased ability of muscle cells to produce ATP, resulting in decreased ability of the muscles to contract B. decreased ability to synthesize acetylcholine in the neurons that innervate the thigh muscles C. decreased synthesis of muscle proteins and/or increased breakdown of muscle proteins D. none of the above

Muscle tissue grows and heals in response to stress. Without the stress of exercise and normal daily activities, muscle tissue degenerates.

Thick myofilaments are made of ________. A.actin B.myosin C.tropomyosin D.troponin

Myosin, a contractile protein, is the principal component of the thick myofilaments.

A. axon B. axon terminal C. synaptic cleft D. sarcolemma

Overall, an electrical signal in the motor neuron's axon leads to an electrical signal in the muscle fiber's sarcolemma. However, the electrical signal is briefly converted to a chemical signal as the information crosses the synaptic cleft.

Muscle tissue does NOT ________. A. maintain posture B. stabilize joints C. produce blood cells D. produce movement

Producing blood cells is a function of red bone marrow, not a function of muscle tissue.

Skeletal muscle cells are grouped into bundles called __________. A. muscle fibers B.fascicles C.myofibrils D. myofilaments

Skeletal muscle cells (or muscle fibers) are grouped into fascicles that resemble bundles of sticks.

Which muscle fiber type is best suited for endurance activities, such as long-distance jogging? A. fast oxidative fibers B. fast glycolytic fibers C. slow glycolytic fibers D. slow oxidative fibers

Slow oxidative fibers are best suited for endurance (long duration) activities because they produce ATP aerobically, and are thus, fatigue-resistant. Fast glycolytic fibers, and to a lesser extent fast oxidative fibers, rely more on anaerobic glycolysis, and thus produce more lactic acid, which is a major cause of fatigue.

Slow oxidative muscle fibers are best suited for ________. A. running a 100-yard dash B. running a marathon C. lifting heavy weights at the gym D. hitting a baseball

Slow oxidative muscle fibers are best suited for endurance activities, such as long distance running, cycling, or rowing.

The type of muscle found in the walls of most hollow organs is ________. A. unitary smooth muscle B. multi unit smooth muscle C. skeletal muscle D. cardiac muscle

Smooth muscle is generally classified as being either unitary smooth muscle or multi unit smooth muscle. The type of muscle found in the walls of most hollow organs is unitary smooth muscle.

Smooth muscles are able to regenerate throughout life. A.True B.False C. D.

Smooth muscles are able to regenerate throughout life. In contrast, cardiac and skeletal muscle cells stop dividing early in life, but they retain the ability to lengthen and thicken in a growing child and to hypertrophy in adults.

Which of the following factors influence the velocity and duration of muscle contraction? A. muscle fiber size B. frequency of stimulation C. length of muscle fibers activated D. load placed on the muscle

Speed (velocity) of shortening is a function of load and muscle fiber type. Contraction is fastest when the load on the muscle is zero; a greater load results in a slower contraction and a shorter duration of contraction.

What special feature of smooth muscle allows it to stretch without immediately resulting in a strong contraction? A. smooth muscle tone B. low energy requirements C. stress-relaxation response D. slow, prolonged contractile activity

Stretching of smooth muscle provokes contraction; however, the increased tension persists only briefly, and soon the muscle adapts to its new length and relaxes, while still retaining the ability to contract on demand. The stress-relaxation response of smooth muscle allows a hollow organ to fill or expand slowly to accommodate a greater volume without promoting strong contractions that would expel its contents.

Binding of calcium to calmodulin is a step in excitation-contraction coupling of ________ cells. A. cardiac muscle B. skeletal muscle C. cardiac and visceral smooth muscle D. smooth muscle

The calcium calmodulin system of contraction regulation is found only in smooth muscle. Excitation-contraction coupling in skeletal muscle and cardiac muscle involves the binding of calcium to troponin (not calmodulin).

The first step toward generating a skeletal muscle contraction is ________. A. binding of the myosin heads to actin B. stimulation of the muscle by a nerve ending C. a rise in intracellular Ca2+ levels D. binding of ATP to the myosin heads

The first step toward generating a skeletal muscle contraction is nervous stimulation of the muscle fiber in order to generate an action potential. The site of muscle stimulation, where the nerve ending communicates with the muscle fiber, is called the neuromuscular junction.

The force of a muscle contraction is NOT affected by __________. A. the frequency of the stimulation B. the size of the muscle fibers stimulated C. the number of muscle fibers stimulated D. the amount of ATP stored in the muscle cells

The force of a muscle contraction is NOT affected by the amount of ATP stored in the muscle cells. Instead of relying on storage of ATP, muscle cells use ATP regenerating pathways, such as glycolysis, to meet the ATP demands of muscle contraction.

When the chemically gated ion channels open, which ion is mainly responsible for depolarizing the sarcolemma? A. ACh B. sodium C.calcium D.potassium

The inward diffusion of sodium ions, through acetylcholine receptors, depolarizes the sarcolemma. Potassium also diffuses through acetylcholine receptors, but less potassium diffuses than sodium, and the outward movement of potassium is not depolarizing.

Which of the following best describes how ACh changes the ion permeability of the sarcolemma? A. ACh entry into the muscle fiber causes Ca2+ to be released by the sarcoplasmic reticulum. B. ACh binds to receptors in the junctional folds. C. ACh activates acetylcholinesterase. D. ACh entry into the axon terminal causes neurotransmitter release.

The junctional folds of the muscle fiber's sarcolemma contain ACh receptors. These receptors are chemically gated ion channels. When ACh binds to these receptors, they open, allowing ions to diffuse across the sarcolemma. This represents an increase in the sarcolemma's ion permeability.

The major role of the sarcoplasmic reticulum is to regulate ________. A. intracellular levels of Na+ B. extracellular levels of Na+ C. intracellular levels of Ca2+ D. extracellular levels of Ca2+

The major role of the sarcoplasmic reticulum is to regulate intracellular Ca2+ levels. The sarcoplasmic reticulum stores ionic calcium when the muscle is relaxed and releases it when the muscle fiber is stimulated to contract.

Which organelle contains the contractile elements found in skeletal muscle? A.sarcolemma B. sarcoplasmic reticulum C. myofibril D.glycosome

The myofibrils contain the contractile elements of skeletal muscles, the sarcomeres. The sarcomeres contain even smaller rod-like structures called myofilaments.

ACh receptors are found mainly in the __________. A. synaptic vesicles B. terminal cisternae C.sarcolemma D. axon terminal

The sarcolemma contains ACh receptors. The opening of these ACh receptors depolarizes the muscle fiber, which leads to the generation of a muscle action potential.

The sliding filament model of contraction states that ________. A. during contraction the thin myofilaments slide past T tubules so that the Z discs are overlapping B. during contraction the thin myofilaments slide past the thick myofilaments so that calcium ions can be released from the sarcoplasmic reticulum C. during contraction the thin myofilaments slide past the thick myofilaments so that the actin and myosin myofilaments overlap to a greater degree D. during contraction the thin myofilaments slide past the thick myofilaments so that the actin and myosin myofilaments no longer overlap

The sliding filament model of contraction states that during contraction, the thin myofilaments slide past the thick myofilaments so that actin and myosin myofilaments overlap to a greater degree. In a relaxed muscle fiber, the thick and thin myofilaments overlap only at the ends of the A band.

Myasthenia gravis is sometimes treated medically by a treatment that involves ________. A. boosting the activity of the immune system B. suppressing the synthesis of acetylcholine C. suppressing the release of acetylcholine from synaptic vesicles D. inhibiting the action of acetylcholinesterase

This enzyme breaks down acetylcholine into acetic acid and choline.

Which of the following is TRUE? A. Skeletal muscle lacks the coarse connective tissue sheaths that are found in smooth muscle. B. Skeletal muscle fibers tend to be shorter than smooth muscle fibers. C. Skeletal muscle cells have one nucleus, but smooth muscle cells are multinucleated. D. Skeletal muscle fibers contain sarcomeres; smooth muscle fibers do not.

This is true; skeletal muscle fibers contain sarcomeres (and are thus striated); smooth muscle fibers do not (and are thus nonstriated).

Which protein inhibits interaction between actin and myosin to prevent skeletal muscle contraction; and which ions remove the inhibition? A. myosin; sodium ions B. tropomyosin; calcium ions C. actin; calcium ions D. troponin; sodium ions

Tropomyosin, a regulatory protein, blocks the myosin binding sites on the actin molecules, preventing myosin heads from binding to actin to form cross bridges. When calcium ions bind to the TnC subunit of a troponin complex, troponin changes shape and moves tropomyosin away from its inhibitory position. As a result, the energized myosin heads (of thick myofilaments) can bind to the actin molecules (of thin myofilaments) and begin the cross bridge cycle, which shortens (contracts) the muscle fiber.

When muscle cells break down glucose to generate ATP under oxygen deficient conditions, they will form ________. A.glucose B.glycogen C. fatty acids D. lactic acid

Under anaerobic conditions, (oxygen deficient conditions) most of the pyruvic acid produced during glycolysis (breakdown of glucose) will be converted to lactic acid rather than enter the mitochondria to participate in aerobic respiration.

What structure is the functional unit of contraction in a skeletal muscle fiber? A. The sarcomere B. The triad C. The junctional folds of the sarcolemma D. The cross bridge

Yes! A sarcomere is a regular arrangement of thin and thick myofilaments that extends from one Z disc to the next. A myofibril consists of a series of sarcomeres.

Which of the following is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers? A. Sodium ions. B. Acetylcholine. C. Calcium ions. D. Action potentials.

Yes! Action potentials propagating down the T-tubule cause a voltage-sensitive protein to change shape. This shape change opens calcium release channels in the sarcoplasmic reticulum, allowing calcium ions to flood the sarcoplasm. This flood of calcium ions is directly responsible for the coupling of excitation to contraction in skeletal muscle fibers.

The cross bridge cycle is a series of molecular events that occur after excitation of the sarcolemma. What is a cross bridge? A. Troponin bound to tropomyosin B. A myosin head bound to actin C. ATP bound to a myosin head D. Calcium bound to troponin

Yes! As soon as the activated myosin head forms a cross bridge with actin, the power stroke begins.

How does the myosin head obtain the energy required for activation? A. The energy comes from oxidative phophorylation. B. The energy comes from the hydrolysis of ATP. C. The energy comes from the hydrolysis of GTP. D. The energy comes from the direct phosphorylation of ADP by creatine phosphate.

Yes! Myosin is a large, complex protein with a binding site for actin. It also contains an ATPase. The energy released during the hydrolysis of ATP activates the myosin head.

Excitation of the sarcolemma is coupled or linked to the contraction of a skeletal muscle fiber. What specific event initiates the contraction? A. Sodium release from the sarcoplasmic reticulum initiates the contraction. B. Calcium release from the sarcoplasmic reticulum initiates the contraction. C. Action potentials propagate into the interior of the skeletal muscle fiber. D. Voltage-sensitive proteins change shape.

Yes! Sarcoplasmic reticulum is the specific name given to the smooth endoplasmic reticulum in muscle cells. It is especially abundant and convoluted in skeletal muscle cells. It functions in the storage, release, and reuptake of calcium ions.

Calcium ions couple excitation of a skeletal muscle fiber to contraction of the fiber. Where are calcium ions stored within the fiber? A. Calcium ions are stored in the transverse tubules. B. Calcium ions are stored in the nuclei. C. Calcium ions are stored in the mitochondria. D. Calcium ions are stored in the sarcoplasmic reticulum.

Yes! Sarcoplasmic reticulum is the specific name given to the smooth endoplasmic reticulum in muscle fibers. The sarcoplasmic reticulum is very elaborate in skeletal muscle fibers, allowing for significant storage of calcium ions.

What is name given to the regularly spaced infoldings of the sarcolemma? A. motor endplates B. transverse or T tubules C. terminal cisternae D. sarcoplasmic reticulum

Yes! T tubules penetrate a skeletal muscle fiber and provide a pathway for excitation into the interior.

After a power stroke, the myosin head must detach from actin before another power stroke can occur. What causes cross bridge detachment? A. Calcium ions bind to troponin. B. Acetylcholine binds to receptors in the junctional folds of the sarcolemma. C. ADP and inorganic phosphate are bound to the myosin head. D. ATP binds to the myosin head.

Yes! The binding of ATP to the myosin head weakens the bond between myosin and actin, forcing the myosin head to detach. ATP also provides the energy for the next power stroke.

When does cross bridge cycling end? A. Cross bridge cycling ends when ATP binds to the myosin head. B. Cross bridge cycling ends when calcium ions are passively transported back into the sarcoplasmic reticulum. C. Cross bridge cycling ends when calcium release channels in the sarcoplasmic reticulum open. D. Cross bridge cycling ends when sufficient calcium has been actively transported back into the sarcoplasmic reticulum to allow calcium to unbind from troponin.

Yes! The sarcoplasmic reticulum contains Ca2+-ATPases that actively transport Ca2+ into the SR. Without Ca2+, troponin returns to its resting shape, and tropomyosin glides over and covers the myosin binding sites on actin.

What specific event triggers the uncovering of the myosin binding site on actin? A. Calcium release channels open in the sarcoplasmic reticulum, and calcium levels rise in the sarcoplasm. B. Sodium ions bind to troponin and change its shape. C. Calcium ions bind to troponin and change its shape. D. Calcium ions bind to tropomyosin and change its shape.

Yes! The shape change caused by the binding of calcium to troponin shifts tropomyosin away from the myosin binding sites on actin.

What is the relationship between the number of motor neurons recruited and the number of skeletal muscle fibers innervated? A. A skeletal muscle fiber is innervated by multiple motor neurons. B. Motor neurons always innervate thousands of skeletal muscle fibers. C. A motor neuron typically innervates only one skeletal muscle fiber. D. Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron.

Yes! There are many more skeletal muscle fibers than there are motor neurons. The ratio of neurons to fibers varies from approximately one to ten to approximately one to thousands.

A triad is composed of a T-tubule and two adjacent terminal cisternae of the sarcoplasmic reticulum. How are these components connected? A. A series of proteins that control calcium release. B. Voltage-gated sodium channels. C. Myosin cross-bridge binding sites. D. Potassium leak channels.

Yes! When action potentials propagate along T-tubules, a voltage-sensitive protein changes shape and triggers a different protein to open it's channels, resulting in the release of calcium from the terminal cisternae.

What is the type of chemical reaction used to rebuild ADP into ATP? A.hydrolysis B. rehydration synthesis C. dehydration synthesis D.

Yes, a water molecule is removed, thus it is called dehydration synthesis. Building ATP from ADP requires a synthetic enzyme plus a source of energy to rebuild the high energy bond.

In a neuromuscular junction, synaptic vesicles in the motor neuron contain which neurotransmitter? A.dopamine B. acetylcholine (ACh) C.serotonin D. norepinephrine

Yes, acetylcholine is the neurotransmitter found in neuromuscular junctions.

What causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum within a muscle cell? A.ATP B. arrival of an action potential C. calcium ion pump D. troponin

Yes, an action potential in the T tubule causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum.

The action potential on the muscle cell leads to contraction due to the release of calcium ions. Where are calcium ions stored in the muscle cell? A. T tubule B. sarcolemma C. terminal cisterns (cisternae) of the sarcoplasmic reticulum D. cytosol

Yes, calcium is stored in the terminal cisterns (cisternae) of the sarcoplasmic reticulum until it is released by an action potential.

Which of the following processes produces molecules of ATP and has two pyruvic acid molecules as end products? A. Krebs cycle and oxidative phosphorylation B.glycolysis C. hydrolysis of creatine phosphate D.

Yes, glucose is broken down in the process called glycolysis. This process takes place in the cytoplasm and does not require oxygen - hence it is called anaerobic respiration. If oxygen is available, the pyruvic acid moves into the mitochondria and glycolysis contributes to aerobic respiration.

The binding of the neurotransmitter to receptors on the motor end plate causes which of the following to occur? A. Binding causes voltage-gated sodium channels to open in the motor end plate (junctional folds of the sarcolemma) and sodium enters the cell. B. Binding of the neurotransmitter causes chemically gated sodium channels to open in the motor end plate (junctional folds of the sarcolemma) and sodium enters the cell. C. Binding causes potassium voltage-gated channels to open in the motor end plate (junctional folds of the sarcolemma) and potassium enters the cell. D. Binding causes chemically gated potassium channels to open in the motor end plate (junctional folds of the sarcolemma) and potassium enters the cell.

Yes, sodium enters the cell and causes depolarization. A small amount of potassium also leaves the motor end plate (junctional folds of the sarcolemma).

When an action potential arrives at the axon terminal of a motor neuron, which ion channels open? A. voltage-gated potassium channels B. chemically gated calcium channels C. voltage-gated calcium channels D. voltage-gated sodium channels

Yes, the action potential opens voltage-gated calcium channels and calcium rushes into the axon terminal, leading to the release of the neurotransmitter.

What causes the myosin head to disconnect from actin? A. binding of troponin B. binding of ATP C. binding of calcium D. hydrolysis of ATP

Yes, the binding of ATP causes the myosin head to disconnect from actin.

What causes the power stroke? A. release of ADP and Pi B.calcium C. binding of ATP D. hydrolysis of ATP

Yes, the hydrolysis of ATP provides the energy for the power stroke. Energy is transferred from ATP to the myosin head.

A myosin head binds to which molecule to form a cross bridge? A.troponin B.actin C.tropomyosin D.

Yes, the myosin head binds to actin, the major component of thin filaments.

What means of membrane transport is used to release the neurotransmitter into the synaptic cleft? A. a channel B. a protein carrier C. exocytosis D.

Yes, the synaptic vesicles (where the neurotransmitter is stored) merge with the membrane and release the neurotransmitter by exocytosis.

The binding of calcium to which molecule causes the myosin binding sites to be exposed? A.tropomyosin B.myosin C.troponin D.actin

Yes, when calcium binds to troponin, troponin releases tropomyosin, exposing the myosin binding sites.