Ch.9 Muscular System

The molecular interaction described as a cross bridge involves the binding of which two proteins? A and B A and D A and C B and D

A and C

Which event causes cross bridge detachment? nervous input ends release of calcium from troponin release of ADP and inorganic phosphate from the myosin head ATP binding to the myosin head

ATP binding to the myosin head As ATP binds, the myosin head releases from the active site on actin

What is the role of calcium in the cross bridge cycle? Calcium binds to myosin, causing the myosin head to release from the actin myofilament. Calcium binds to troponin, altering its shape. Calcium binds to active sites on actin, forming the cross bridge. Calcium binds to troponin, exposing the active site on troponin.

Calcium binds to troponin, altering its shape. Calcium binding to troponin causes tropomyosin to move away from the active sites on actin.

Which selection correctly describes the role of calcium in coupling? -Calcium binds to actin, which triggers troponin to fall off and expose myosin-binding sites. -Calcium binds to actin, which triggers it to bind to myosin. -Calcium binds to troponin, which moves tropomyosin and exposes the myosin-binding sites on actin. -Calcium binds to tropomyosin, which moves tropomyosin and exposes the myosin-binding sites on actin.

Calcium binds to troponin, which moves tropomyosin and exposes the myosin-binding sites on actin. The thin filament in a sarcomere is composed of actin, troponin, and tropomyosin. Troponin and tropomyosin are attached to one another, both overlaying actin. When a muscle is relaxed, tropomyosin blocks actin's myosin-binding sites. Calcium binds to troponin, initiating a shape change that removes the blocking action of tropomyosin. This exposes the myosin-binding sites on actin to the myosin heads for cross bridging.

Which of the following is responsible for muscle relaxation? Calcium ions are released from the terminal cisterns during depolarization of the T tubule. Sodium ions enter into the sarcoplasm through voltage-gated channels. Calcium ions are removed from the sarcoplasm by active transport. ATP binds to the myosin head to cause cross bridge detachment.

Calcium ions are removed from the sarcoplasm by active transport. Removal of calcium ions lowers the calcium ion concentration below the threshold for muscle contraction.

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

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.

How do calcium ions initiate contraction in skeletal muscle fibers? Calcium ions bind to tropomyosin, exposing the active sites on actin. Calcium ions provide the energy necessary for the myosin head power stroke. Calcium ions bind to troponin, changing troponin's shape. Calcium ion movement depolarizes the sarcolemma at the synaptic cleft.

Calcium ions bind to troponin, changing troponin's shape. The shape change in troponin, caused by calcium binding, causes a shift in the position of tropomyosin along the thin filament. This exposes active sites to myosin and allows cross bridges to form. The cycling of cross bridges is what creates tension during contraction.

Which of the following is true about smooth muscle? Smooth muscle, in contrast to skeletal muscle, cannot synthesize or secrete any connective tissue elements. Smooth muscle cannot stretch as much as skeletal muscle. Smooth muscle has well-developed T tubules at the site of invagination. Certain smooth muscle cells can actually divide to increase their numbers.

Certain smooth muscle cells can actually divide to increase their numbers.

A person dies, and within hours, the skeletal muscles develop a locked contraction known as rigor mortis. Calcium ions leak from the sarcoplasmic reticulum into cytoplasm. From your knowledge of cross bridge cycling, what best explains this rigor? The cross bridge is locked up because the power stroke requires ATP, which is produced only during life. Cross bridge formation cannot occur. ATP, which is produced only during life, must to be bound to the myosin head to permit cross bridging. The cross bridge is locked up because ATP directly attaches myosin to actin. Cross bridge detachment cannot occur. Detachment requires ATP, which is produced only during life

Cross bridge detachment cannot occur. Detachment requires ATP, which is produced only during life After ATP attaches to the myosin head, the bond between actin and myosin is weakened and the cross bridge breaks.

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

The sarcomere 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.

If troponin is a component of both cardiac and skeletal muscle, why is an elevated plasma troponin level useful in diagnosing myocardial damage? The subunits of the troponin in cardiac muscle are unique to heart muscle. Patients who have experienced acute cardiac damage often injure their skeletal muscles as they fall to the ground, releasing troponin. Whenever cardiac muscle is damaged, skeletal muscles receive inadequate blood flow and release troponin. Troponin is an important component of all striated muscle, so an increase level of its subunits is a nonspecific indicator of damage to either type of muscle.

The subunits of the troponin in cardiac muscle are unique to heart muscle. Although both types of striated muscle contain troponin, the subunits found in cardiac muscle are different from those in skeletal muscle. The laboratory test used to diagnose cardiac muscle damage is specific for those subunits.

Which of the following best describes the role of muscle fiber triads? The triad allows an action potential to activate voltage-sensitive proteins in a T tubule, which in turn opens calcium channels in the paired terminal cisternae, allowing calcium to flood the sarcomere. Two axon terminals and the one muscle fiber they activate compose a functional neuromuscular triad, or the functional unit of muscle. Acetylcholine, T tubules, and actin create a functional triad that allows acetylcholine to penetrate the sarcolemma, bind to actin, and activate a muscle fiber contraction. A triad is made up of troponin, tropomyosin, and actin. They function together to control when myosin pulls on actin.

The triad allows an action potential to activate voltage-sensitive proteins in a T tubule, which in turn opens calcium channels in the paired terminal cisternae, allowing calcium to flood the sarcomere. A triad describes the grouping of two terminal cisternae with a T tubule that ensures an action potential causes the release of calcium within the myofibril.

Which of the following describes the cells of unitary smooth muscle? They consist of muscle fibers that are structurally independent of each other. They exhibit spontaneous action potentials. They are used for vision and hair raising. They depend upon recruitment using the autonomic nervous system.

They exhibit spontaneous action potentials.

Synaptic vesicles at the neuromuscular junction contain __________. ACh receptors calcium synaptic potentials acetylcholine

acetylcholine 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.

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

acetylcholine (ACh) Yes, acetylcholine is the neurotransmitter found in neuromuscular junctions.

What event most directly triggers the release of calcium from the terminal cisternae? cross bridge formation between the thick and thin filaments movement of tropomyosin away from the active sites on actin action potential propagating toward the axon terminal action potential propagating down the T tubule

action potential propagating down the T tubule The action potential propagating down the T tubule causes voltage sensitive tubule proteins to change shape, which opens calcium release channels in the terminal cisternae.

What causes the myosin head to disconnect from actin? binding of troponin binding of calcium binding of ATP hydrolysis of ATP

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

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

broken down by acteylcholinesterase 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.

Myofilaments represent which organizational level of anatomy? organ level cellular level chemical level tissue level

chemical level The chemical level of anatomy refers to the atoms and molecules that make up the parts of the body. Myofilaments are protein structures. Proteins are large molecules.

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

decreased synthesis of muscle proteins and/or increased breakdown of muscle proteins Muscle tissue grows and heals in response to stress. Without the stress of exercise and normal daily activities, muscle tissue degenerates.

An anaerobic metabolic pathway that results in the production of two net ATPs per glucose plus two pyruvic acid molecules is ________. glycolysis hydrolysis the electron transport chain the citric acid cycle

glycolysis

Which of the following is a factor that affects the velocity and duration of muscle contraction? size of the muscle fibers stimulated. number of muscle fibers stimulated. muscle length. load on the fiber.

load on the fiber

Which of the following would be recruited later in muscle stimulation when contractile strength increases? motor units with larger, less excitable neurons. large motor units with small, highly excitable neurons. many small motor units with the ability to stimulate other motor units. motor units with the longest muscle fibers.

motor units with larger, less excitable neurons

Which term best identifies a muscle cell? sarcomere muscle fascicle myofibril muscle fiber

muscle fiber Skeletal muscle cells fuse during development to form the mature, multinucleated muscle fibers.

What, specifically, is a cross bridge? myosin binding to actin ATP binding to the myosin head calcium binding to troponin tropomyosin covering the active sites on actin

myosin binding to actin The attachment of a myosin head from the thick filament to an active site on actin on the thin filament is a cross bridge. As soon as the cross bridge forms, the power stroke occurs, moving the thin filament toward the center of the sarcomere.

What causes the power stroke? hydrolysis of ATP release of ADP and Pi calcium binding of ATP

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

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

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

ACh receptors are found mainly in the __________. -synaptic vesicles -sarcolemma -axon terminal -terminal cisternae

sarcolemma 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.

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

simple diffusion away from the synaptic cleft and acetylcholinesterase (AChE; an enzyme) Acetylcholinesterase breaks down acetylcholine in the synaptic cleft.

Reduction in blood flow to a muscle fiber would have the greatest effect on ________. fast oxidative fibers fast glycolytic slow oxidative fibers both slow and fast oxidative

slow oxidative fibers

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

slow oxidative fibers Slow oxidative fibers are best suited for endurance activities because they produce ATP aerobically and are fatigue-resistant.

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

sodium 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.

Myoglobin ________. produces the end plate potential breaks down glycogen is a protein involved in the direct phosphorylation of ADP stores oxygen in muscle cells

stores oxygen in muscle cells

Creatine phosphate functions in the muscle cell by ________. inducing a conformational change in the myofilaments storing energy that will be transferred to ADP to resynthesize ATP forming a temporary chemical compound with myosin forming a chemical compound with actin

storing energy that will be transferred to ADP to resynthesize ATP

The calcium that initiates skeletal muscle contraction is released from what structure(s)? terminal cisternae T tubules sarcolemma sarcomeres

terminal cisternae The terminal cisternae release calcium, which is the "go" signal for a muscle contraction. The terminal cisternae are the enlarged ends 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? terminal cisterns (cisternae) of the sarcoplasmic reticulum cytosol T tubule sarcolemma

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

What does excess postexercise oxygen consumption represent? the difference between the amount of oxygen needed for totally aerobic muscle activity and the amount actually used the amount of oxygen taken into the body immediately after the exertion amount of oxygen needed for aerobic activity to accomplish the same amount of work the amount of oxygen equal to the oxygen already used

the difference between the amount of oxygen needed for totally aerobic muscle activity and the amount actually used

A toxin released by certain bacteria can block the release of neurotransmitters into a neuromuscular synapse. What would result from such a block? the loss of ability to contract the muscle The muscle would become permanently contracted. The muscle would remain fixed at the length it was when the toxin contacted it.

the loss of ability to contract the muscle Without acetylcholine, the muscle would not be able to contract or even maintain tone.

An action potential is propagated down the sarcolemma as a result of which of the following? the closing of potassium channels the opening of voltage-gated potassium channels the closing of voltage-gated sodium channels the opening of voltage-gated sodium channels

the opening of voltage-gated sodium channels As voltage-gated sodium channels are opened, the influx of positively charged sodium ions locally changes the charge of the sarcolemma. This opens more voltage-gated sodium channels farther down the sarcolemma.

The __________ shorten(s) during muscle contraction sarcomere actin thick filament Z lines

the sarcomere As actin slides over myosin, the z lines are pulled closer together, shortening the sarcomere.

The contractile, or functional, unit of a muscle fiber is __________. troponin the sarcomere the myofilament the elastic filament

the sarcomere The sarcomere is the contractile unit of a muscle fiber and the smallest functional unit of muscle. A sarcomere is the region of a myofibril between two successive Z discs; it primarily consists of thin and thick myofilaments.

The mechanism of contraction in smooth muscle is different from skeletal muscle in that ________. actin and myosin interact by the sliding filament mechanism the trigger for contraction is a rise in intracellular calcium ATP energizes the sliding process the site of calcium binding site differs

the site of calcium binding site differs

Although all the anatomical parts of muscle work together to give it it's characteristics, which of the following proteins listed below would be most associated with the characteristics of contractility? potassium (K+) leak channels. elastic (titin) filaments. thick (myosin) filaments. voltage gated sodium channels.

thick (myosin) filaments

A potential benefit of recruiting slow oxidative fibers for contraction before recruiting fast oxidative and fast glycolytic fibers might be ________. because they are slower to respond, slow oxidative fibers must be stimulated first in order to contract simultaneously with the faster fibers to allow for fine control with delicate contractile force with a small stimulus recruiting slow oxidative fibers early helps to tire them out first so that they won't interfere with the more powerful contractions of fast glycolytic fibers There is little to no benefit from recruiting slow oxidative fibers first, and therefore it is in fact fast glycolytic fibers that will be recruited first.

to allow for fine control with delicate contractile force with a small stimulus

An enzyme known as acetylcholinesterase is present in the synaptic cleft. What is its role? to facilitate the entrance of acetylcholine into the muscle cell to facilitated transport of acetylcholine across the cleft to pump Ca2+ back out of the axon terminal to break down acetylcholine

to break down acetylcholine Acetylcholinesterase breaks acetylcholine apart, terminating the synaptic transmission. Choline can be taken back into the axon terminal and reused.

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

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

In muscle fibers, which regulatory protein blocks the attachment of myosin heads to actin? thick filaments calcium tropomyosin acetylcholinesterase

tropomyosin Tropomyosin covers the active site on actin, preventing cross bridge formation.

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

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

Which type of muscle fiber has a large quantity of glycogen and mainly uses glycolysis to synthesize ATP? red slow twitch fibers white fast twitch fibers

white fast twitch fibers Yes, white fast twitch fibers have high glycogen content for a readily available source of glucose for glycolysis. They appear white because of the reduced amount of myoglobin and fewer capillaries surrounding them. Because these fibers have reduced myoglobin and very few capillaries surrounding them, they have very little oxygen available for the Krebs cycle and oxidative phosphorylation. They also have fewer mitochondria (where the Krebs cycle and oxidative phosphorylation would take place).

BMD (2,3-butanedione 2-monoximime) inhibits myosin, such that ATP can bind to myosin but myosin is unable to hydrolyze the bound ATP. What effect would BMD have on the cross bridge cycle? Myosin heads would remain detached, unable to cock. Tropomyosin would not move, and the active sites on actin would not be exposed. Myosin heads would remain attached to actin, unable to perform the power stroke. Myosin heads would remain attached to actin, unable to detach.

Myosin heads would remain detached, unable to cock. The hydrolysis of ATP is required for the cocking of the myosin head. ATP would still bind to myosin, causing cross bridge detachment, but myosin would be stuck in this step of the cross bridge cycle.

Calcium entry into the axon terminal triggers which of the following events? Synaptic vesicles fuse to the plasma membrane of the axon terminal and release acetylcholine. Cation channels open and sodium ions enter the axon terminal while potassium ions exit the axon terminal. Acetylcholine binds to its receptor. Acetylcholine is released into the cleft by active transporters in the plasma membrane of the axon terminal

Synaptic vesicles fuse to the plasma membrane of the axon terminal and release acetylcholine. Yes! When synaptic vesicles fuse to the plasma membrane, acetylcholine is released via exocytosis.

The binding of calcium to which molecule causes the myosin binding sites to be exposed? myosin tropomyosin troponin actin

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

The smallest contractile unit within skeletal muscle would correspond to the distance between which two points in the figure? 2 and 6 1 and 3 3 and 5 1 and 7

1 and 7

Which of the following is/are mechanism(s) to end neural transmission at the neuromuscular junction? Select all the correct answers. ACh is broken down into acetic acid and choline by the enzyme acetylcholinesterase (AChE). ACh is taken up by the axon terminal via endocytosis. ACh diffuses away from the synaptic cleft. ACh binds to ACh receptors.

1. ACh is broken down into acetic acid and choline by the enzyme acetylcholinesterase (AChE). 2. ACh diffuses away from the synaptic cleft. The chemical signal (ACh) at the neuromuscular junction is very short! Soon after ACh is released from the axon terminal, it is rapidly degraded by AChE or diffuses out of the synaptic cleft. These two mechanisms ensure that just enough ACh binds to its receptor to initiate an action potential and that the muscle fiber's response is quickly terminated.

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

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

Which of the following choices best summarizes excitation-contraction coupling? -A series of events in which actin binds myosin to enact contraction -A series of events in which an action potential triggers the release of chemical messengers -A series of events in which an electrical stimulus is conveyed to a muscle fiber to enact contraction -A series of events in which calcium gradients are used to convey a signal to the muscle fiber to enact contraction

A series of events in which an electrical stimulus is conveyed to a muscle fiber to enact contraction Congratulations! You have completed the final activity in this tutorial. The tutorial covered the sequence of events in excitation-contraction coupling that links the excitation of the membrane to the cross bridge cycling of the contracting proteins. Great job!

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

A series of proteins that control calcium release. 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.

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

ACh binds to receptors in the junctional folds. 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.

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

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.

Which of the following occurs during cross bridge cycling? The troponin-tropomyosin complex blocks the active sites on actin. Actin binds to myosin, pulling myosin heads closer to the M line of the sarcomere. ATP is hydrolyzed in order to put the myosin head in a high-energy position. ATP is hydrolyzed to activate the binding of myosin to active sites on actin.

ATP is hydrolyzed in order to put the myosin head in a high-energy position. ATP must be available to ready the myosin molecule in its "cocked" position.

Action potential propagation in a skeletal muscle fiber ceases when acetylcholine is removed from the synaptic cleft. Which of the following mechanisms ensures a rapid and efficient removal of acetylcholine? Acetylcholine is transported into the postsynaptic neuron by receptor-mediated endocytosis. Acetylcholine is transported back into the axon terminal by a reuptake mechanism. Acetylcholine is degraded by acetylcholinesterase. Acetylcholine diffuses away from the cleft.

Acetylcholine is degraded by acetylcholinesterase. Yes! Acetylcholinesterase is an enzyme that degrades acetylcholine. This degradation results in a rapid cessation of the acetylcholine signal and a swift removal from the cleft.

The neuromuscular junction is a well-studied example of a chemical synapse. Which of the following statements describes a critical event that occurs at the neuromuscular junction? Acetylcholine binds to its receptor in the junctional folds of the sarcolemma. Its receptor is linked to a G protein. Acetylcholine is released by axon terminals of the motor neuron. Acetylcholine is released and moves across the synaptic cleft bound to a transport protein. When the action potential reaches the end of the axon terminal, voltage-gated sodium channels open and sodium ions diffuse into the terminal.

Acetylcholine is released by axon terminals of the motor neuron. Yes! Acetylcholine is released into the synaptic cleft via exocytosis.

Which of the following best describes the role of acetylcholinesterase molecules at the neuromuscular junction? Acetylcholinesterase prevents Na+ and K+ from passing through chemically gated ion channels. Acetylcholinesterase binds ACh, preventing it from binding to chemically gated ion channels. Acetylcholinesterase breaks down ACh, which allows chemically gated ion channels to close. Acetylcholinesterase molecules close once ACh is released, which decreases the sarcolemma's permeability to Na+ and K+.

Acetylcholinesterase breaks down ACh, which allows chemically gated ion channels to close. The chemical signal at the neuromuscular junction is quite brief. As soon as ACh is released from the axon terminal, acetylcholinesterase molecules in the synaptic cleft begin to break it down. This ensures that ACh receptors are open only for the brief amount of time required to initiate an action potential in the muscle fiber.

What is the fate of acetylcholine (Ach) after it binds to Ach receptors? Ach is broken down by acetylcholinesterase. Ach enters the muscle fiber, contributing to the end plate potential. Ach passes down the T tubules and triggers the release of calcium from the sarcoplasmic reticulum. Ach is directly reabsorbed into the axon terminal for reuse.

Ach is broken down by acetylcholinesterase. The effects of acetylcholine must be terminated to prevent sustained muscle cell contraction.

How/when does the myosin head cock back to store energy for the next cycle? The power stroke cocks the myosin head. The sliding of the actin myofilament during the power stroke re-cocks myosin heads that have previously delivered their power stroke. After the myosin head detaches, energy from ATP hydrolysis is used to re-cock the myosin head. when ADP is released from the myosin head

After the myosin head detaches, energy from ATP hydrolysis is used to re-cock the myosin head. In addition to breaking the cross bridge, ATP provides energy to cock the heads back after the previous power stroke.

Consider how the action potential that initiates contraction is delivered to the muscle cell. Which of the choices below correctly describes how an action potential generated at the neuromuscular junction (NMJ) is converted to excitation in the muscle fiber? ACh binds at a receptor in the motor neuron, which initiates graded potentials. An action potential in the motor neuron directly triggers an action potential at the sarcolemma. An action potential in the motor neuron causes ACh to be released into the synaptic cleft. Binding of ACh at the membrane receptor initiates a direct action potential. An action potential in the motor neuron causes ACh to be released into the synaptic cleft. Binding of ACh to sarcolemma receptors initiates graded potentials.

An action potential in the motor neuron causes ACh to be released into the synaptic cleft. Binding of ACh to sarcolemma receptors initiates graded potentials. Yes! An action potential traveling down a motor neuron arrives at the axon terminal and causes exocytosis of the neurotransmitter ACh into the synaptic cleft. ACh diffuses into the synaptic cleft, binds to the receptor proteins on the junctional folds of the muscle sarcolemma (motor end plate), and initiates graded potentials. These graded potentials sum to an action potential, thus initiating excitement of the muscle fiber.

What causes the release of calcium ions into the sarcoplasm from the terminal cisterns? An action potential traveling along the t tubule The change in the shape of troponin Acetylcholine entering the sarcoplasm of the muscle fiber The binding of myosin heads to actin

An action potential traveling along the t tubule In response to an action potential traveling along the t tubule, voltage-sensitive proteins change shape, opening calcium channels in the adjacent terminal cisterns of the sarcoplasmic reticulum.

What action is directly responsible for the generation of an action potential at the sarcolemma? The sodium-potassium pump must restore the ionic concentrations inside and outside the cell. An end plate potential sufficient to reach threshold must be produced. Sodium ions must be released from the muscle cell. Calcium ions bind to troponin-tropomyosin complex in order to expose the active sites on actin.

An end plate potential sufficient to reach threshold must be produced. If an end plate potential occurs, voltage-gated sodium channels open, propagating an action potential that will be conducted along the sarcolemma.

Which of the following interactions must occur first so that the others can take place? D is shifted from actin's binding sites. B binds to troponin. C binds to actin. C releases ADP and P.

B binds to troponin. Binding of calcium (B) to troponin 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.

Which statement accurately describes the event indicated by B? The binding of acetylcholine directly causes the formation of a wave of depolarization. Diffusion of Ca2+ into the muscle fiber triggers the diffusion of acetylcholine out of the muscle fiber. Binding of acetylcholine to a receptor triggers the opening of an ion channel. Diffusion of acetylcholine into the muscle fiber triggers the opening of an ion channel.

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

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

Which of the following is most directly required to initiate the coupling of myosin to actin? Ca++ ATP ACh glucose

Ca++ Ca++ binds to troponin, which removes tropomyosin from the myosin binding site on actin.

The cross bridge cycle starts when _________. Select the best answer. ATP binds to troponin and is hydrolyzed to ADP and PiCa2+ from the sarcoplasmic reticulum binds to tropomyosin Ca2+ is actively transported into the sarcoplasmic reticulum acetylcholine diffuses away from the synaptic cleft Ca2+ from the sarcoplasmic reticulum binds to troponin

Ca2+ from the sarcoplasmic reticulum binds to troponin The release of Ca2+ is triggered by the propagation of an action potential along a skeletal muscle fiber. Ca2+ is released from the sarcoplasmic reticulum and into the sarcoplasm of the muscle fiber. When Ca2+ concentration is high in the sarcoplasm, Ca2+ binds to troponin causing change in its shape. This shape change alters the position of tropomyosin and moves it away from myosin binding sites on actin, thus allowing the myosin head to bind actin and form a cross bridge.

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

Calcium ions bind to troponin 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.

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

Calcium release from the sarcoplasmic reticulum initiates the contraction. 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.

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

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.

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? Excitation, in this case, refers to the propagation of action potentials along the sarcolemma. Excitation refers to the propagation of action potentials along the axon of a motor neuron. Excitation refers to the shape change that occurs in voltage-sensitive proteins in the sarcolemma. Excitation refers to the release of calcium ions from the sarcoplasmic reticulum.

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.

Which of the following is NOT a role of ATP in muscle contraction? Detaching the cross bridge from actin Transporting calcium ions into the sarcoplasmic reticulum Exposing myosin binding sites on actin Energizing the power stroke of the cross bridge

Exposing myosin binding sites on actin Exposure of myosin binding sites does not utilize ATP. During excitation-contraction coupling, calcium ions released from the terminal cisterns of the sarcoplasmic reticulum flood into the sarcoplasm. Calcium ions bind to troponin, which changes its conformation to slide tropomyosin away from the myosin binding sites. Therefore, calcium ions, not ATP, are responsible for exposure of the myosin binding sites on actin.

Which of the following statements is NOT true regarding ATP production in muscles during periods of prolonged energy use, such as exercise? 1. In the absence of oxygen, anaerobic pathways provide minimal ATP regeneration for less than a minute. 2. Prolonged activity requires the use of aerobic pathways for ATP regeneration. 3. As your blood sugar drops at any time during prolonged activity, glycogen stores in your muscles can be broken down to supply a glucose source. 4. In the absence of oxygen, creatine phosphate can drive aerobic respiration pathways for a few minutes.

In the absence of oxygen, creatine phosphate can drive aerobic respiration pathways for a few minutes. This is not true for a few reasons. First, creatine phosphate directly phosphorylates ATP instead of providing any support for aerobic pathways. Second, creatine phosphate stores are used up in about 15 seconds. Third, a cell doesn't need an oxygen deficit for creatine phosphate to be activated; it just needs to be short on ATP.

The action potential propagates along the sarcolemma. As the action potential spreads down the T tubules of the triads, voltage-sensitive tubule proteins change shape. How does the shape change of these proteins lead to contraction? -It permits calcium to exit the cistern and enter the T tubule. -It allows calcium to exit the cytoplasm and enter the cisterns. -It allows calcium to exit the sarcoplasmic reticulum and enter the cytosol. -It facilitates ACh's binding to the sarcolemma.

It allows calcium to exit the sarcoplasmic reticulum and enter the cytosol. As the action potential propagates, it changes the shape of T tubule proteins. These proteins are linked to calcium channels in the terminal cisterns of the sarcoplasmic reticulum. When these proteins' calcium channels open, a massive amount of calcium flows into the cytosol.

If the cell could no longer produce ATP, what would be the effect on the sarcoplasmic reticulum? Ca++ would leak out of the cell. The muscle would not contract. It would be unable to concentrate Ca++ in the sarcoplasmic reticulum. Ca++ would build up in the sarcoplasmic reticulum.

It would be unable to concentrate Ca++ in the sarcoplasmic reticulum. To concentrate Ca++ in the sarcoplasmic reticulum, active transport must occur. With no ATP, there would be no active transport.

EGTA is a substance that binds calcium ions. Imagine an experimental setup with a motor neuron and a muscle fiber. Stimulation of the motor neuron causes contraction of the muscle fiber through activity at the neuromuscular junction and excitation-contraction coupling. Now, inject the muscle fiber with EGTA. Which of the following effects would EGTA have on excitation-contraction coupling after the neuron releases acetylcholine at the neuromuscular junction? It would prevent myosin from forming cross bridges with actin. It would prevent conduction of an action potential along the sarcolemma. It would prevent the release of calcium ions from the terminal cisterns. It would prevent the junctional folds from triggering an action potential.

It would prevent myosin from forming cross bridges with actin. Calcium ions are the chemical link between the excitation signal or action potential and contraction. Once released from the terminal cisterns, calcium ions bind to troponin, allowing the movement of tropomyosin, and cross bridge formation. If EGTA binds to the calcium ions once they are released, then calcium ions are not available for binding to troponin. Therefore, myosin binding sites will not be exposed, which prevents muscle contraction.

Which of the following processes produces 36 ATP? Krebs cycle and oxidative phosphorylation glycolysis hydrolysis of creatine phosphate

Krebs cycle and oxidative phosphorylation Yes, 36 ATPs are produced for each glucose molecule. This process, which takes place in the mitochondria, is considered aerobic respiration because oxygen is required.

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

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.

Which of the following is true concerning the anatomy of a skeletal muscle fiber? The sarcolemma is the muscle fiber's cytoplasm. T tubules are extensions of the sarcoplasmic reticulum. Myofibrils contain thick and thin filaments. A triad consists of a T tubule and the nearby sarcolemma.

Myofibrils contain thick and thin filaments. Each skeletal muscle fiber contains many myofibrils. And each of these myofibrils contains many thick and thin filaments (myofilaments). These myofilaments are arranged as numerous sarcomeres within the myofibril.

Which selection best describes the initial event in contraction? Calcium binds actin to myosin to begin the cross bridge cycle. The myofilaments slide closer together. Tropomyosin binds to myosin heads and actin bridges with tropomyosin. Myosin heads bind to the newly exposed myosin-binding sites on actin to form cross bridges.

Myosin heads bind to the newly exposed myosin-binding sites on actin to form cross bridges. Contraction begins when myosin binds to actin and forms cross bridges.

If a muscle fiber were to suddenly and permanently stop producing ATP the fiber would no longer be able to actively transport calcium out of the cytoplasm (sarcoplasm) and the intracellular calcium concentration would rise. Which of the following would you expect to happen? Calcium would be transported to the sarcoplasmic reticulum therefore contractions would cease. Myosin would be able to bind to the exposed binding sites on thin filaments but it would not be able to detach. The fiber would twitch uncontrollably due to excessive calcium bound to troponin. No change would occur in a muscle that was relaxed to begin with.

Myosin would be able to bind to the exposed binding sites on thin filaments but it would not be able to detach.

Troponin, a major protein in thin filaments, is a globular protein with three polypeptide subunits. Which of the following is NOT a function of the troponin? One subunit binds tropomyosin and helps position it on actin. One subunit binds to potassium ions. One subunit attaches troponin to actin. One subunit binds to calcium ions.

One subunit binds to potassium ions.

The "rest and recovery" period, where the muscle restores depleted reserves, includes all of the following processes EXCEPT __________. ATP is used to rephosphorylate creatine into creatine phosphate. Pyruvic acid is converted back to lactic acid. Oxygen rebinds to myoglobin. Glycogen is synthesized from glucose molecules

Pyruvic acid is converted back to lactic acid. Yes, this is NOT a part of the "rest and recovery" period. When oxygen is available, lactic acid is converted back to pyruvic acid (not vice versa) that then enters the Krebs cycle. Lactic acid is the end product of the anaerobic pathway.

Inadequate calcium in the neuromuscular junction would directly affect which of the following processes? Conduction of action potentials by the motor neuron Depolarization of the junctional folds Release of acetylcholine from the synaptic vesicles Breakdown of acetylcholine by acetylcholinesterase

Release of acetylcholine from the synaptic vesicles Calcium ions enter the axon terminal when voltage-gated calcium channels open in response to the arrival of an action potential. The presence of calcium causes synaptic vesicles to release acetylcholine into the synaptic cleft.

Of the following items listed below, which is the best description for why skeletal muscle stores glycogen? -Glycogen is part of muscles rigid supporting framework. -Glycogen provides a smooth surface for filaments to slide on. -Skeletal muscle is a heavy consumer of energy. -The glycogen is an insulating layer that helps regulate body temperature.

Skeletal muscle is a heavy consumer of energy.

What role does tropomyosin play in the cross bridge cycle? The displacement of tropomyosin exposes the active sites of actin, allowing cross bridges to form. Tropomyosin pushes the myosin head away, causing cross bridge detachment. Tropomyosin moves the actin filament relative to the myosin filament. Tropomyosin binds to calcium, causing muscle relaxation.

The displacement of tropomyosin exposes the active sites of actin, allowing cross bridges to form. Tropomyosin covers active sites in relaxed muscle. When tropomyosin is displaced, the active sites are exposed for cross bridge formation.

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

The energy comes from the hydrolysis of ATP. 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.

One brief stimulus of a skeletal muscle may result in a single isolated contractile event, which is called a twitch. In a living organism, one twitch can generate max tension in a whole muscle. Are these statements true or false? Both of these statements are false. Both statements are true. The first statement is true; the second statement is false. The first statement is false; the second statement is true.

The first statement is true; the second statement is false. A single stimulation may result in a single muscle twitch. However, a single twitch would not generate any meaningful tension in a skeletal muscle.

Sodium and potassium ions do not diffuse in equal numbers through ligand-gated cation channels. Why? The inside surface of the sarcolemma is negatively charged compared to the outside surface. Potassium ions diffuse inward along favorable chemical and electrical gradients. The outside surface of the sarcolemma is negatively charged compared to the inside surface. Sodium ions diffuse outward along favorable chemical and electrical gradients. The outside surface of the sarcolemma is negatively charged compared to the inside surface. Potassium ions diffuse outward along favorable chemical and electrical gradients. The inside surface of the sarcolemma is negatively charged compared to the outside surface. Sodium ions diffuse inward along favorable chemical and electrical gradients.

The inside surface of the sarcolemma is negatively charged compared to the outside surface. Sodium ions diffuse inward along favorable chemical and electrical gradients. Yes! The resting membrane potential of all cells is negative (inside compared to outside). Therefore, given the direction of the chemical and electrical gradients, more sodium ions diffuse inward than potassium ions diffuse outward.

Based on what you know of the relationship between the thick and the thin filaments, what would happen if a disorder existed that caused a person to produce no tropomyosin? Actin will spontaneously fall apart. The muscle would be weaker than normal. The muscle would never contract. The muscle tissues would never be able to relax.

The muscle tissues would never be able to relax. The tropomyosin covers the myosin binding site on actin. Without tropomyosin, the myosin would constantly have access to those binding sites.

The 100-meter dash is a quick and short run requiring explosive speed. On completion of the dash, the runners will continue to breathe hard for several seconds to minutes even though they are no longer running. Which of the following is the best explanation for why this is so? The runners' fast oxidative muscles are so slow to utilize oxygen, they only begin aerobic respiration by the time the run has finished. Since the exercise was mostly aerobic exercise, the runners' bodies have not yet realized the run is over. Slow oxidative fibers are recruited last and have only started to work at completion of the run. The runners' use of stored oxygen, glucose, and creatine phosphate is being replenished and this requires a prolonged increase of oxygen intake.

The runners' use of stored oxygen, glucose, and creatine phosphate is being replenished and this requires a prolonged increase of oxygen intake.

During contraction, what prevents actin myofilaments from sliding backward when a myosin head releases? There are always some myosin heads attached to the actin myofilament when other myosin heads are detaching. The cross bridge remains in place, preventing the actin myofilament from sliding. The actin myofilament can only move in one direction relative to the myosin filament .Calcium blocks the active sites on actin.

There are always some myosin heads attached to the actin myofilament when other myosin heads are detaching. During contraction, about half of the myosin heads are attached, preventing the actin myofilament from sliding backwards when any single myosin head detaches. The situation is analogous to a game of tug-of-war. In tug-of-war, individual hands release after they pull on the rope, but not all hands release at the same time.

What is the role of tropomyosin in skeletal muscles? Tropomyosin is the receptor for the motor neuron neurotransmitter. Tropomyosin serves as a contraction inhibitor by blocking the myosin binding sites on the actin molecules. Tropomyosin is the chemical that activates the myosin heads. Tropomyosin serves as a contraction inhibitor by blocking the actin binding sites on the myosin molecules.

Tropomyosin serves as a contraction inhibitor by blocking the myosin binding sites on the actin molecules.

How does troponin facilitate cross bridge formation? Troponin hydrolyzes ATP, which provides the energy necessary for cross bridges to form. Troponin gathers excess calcium that might otherwise block actin's progress. Troponin moves away from the active sites on actin, permitting cross bridge formation. Troponin controls the position of tropomyosin on the thin filament, enabling myosin heads to bind to the active sites on actin.

Troponin controls the position of tropomyosin on the thin filament, enabling myosin heads to bind to the active sites on actin. For cross bridges to form, tropomyosin must not block the active sites. The position of tropomyosin is controlled by the regulatory protein troponin. This protein-protein interaction couples the binding of calcium (to troponin) to the exposure of active sites.

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

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.

Which description is most appropriate for a myofibril? a single long cell found within a muscle a single long, thin organelle containing many proteins a single group of long muscle cells surrounded by a membrane a single long protein structure found in the sarcomeres of a muscle cell

a single long, thin organelle containing many proteins A fibril is a very small, fiber-like structure. Since muscle cells are called muscle fibers, the myofibrils are the smaller, fiber-like organelles within a muscle fiber.

Muscle tone is ________. the condition of athletes after intensive training. a state of sustained partial contraction. the ability of a muscle to efficiently cause skeletal movements. the feeling of well-being following exercise

a state of sustained partial contraction

Although all the anatomical parts of muscle work together to give it it's characteristics, which of the following proteins listed below would be most associated with the characteristics of excitability? actin of thin filaments. acetylcholine receptors in the motor end plate. elastic (titin) filaments. the Na+-K+ pump.

acetylcholine receptors in the motor end plate.

After nervous stimulation stops, what prevents ACh in the synaptic cleft from continuing to stimulate contraction? the tropomyosin blocking the myosin once full contraction is achieved acetylcholinesterase breaks apart the ACh calcium ions returning to the terminal cisternae the action potential stops going down the overloaded T tubules

acetylcholinesterase breaks apart the ACh

A myosin head binds to which molecule to form a cross bridge? troponin tropomyosin actin

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

The sliding filament model of contraction involves ________. actin and myosin sliding past each other and partially overlapping the shortening of thick filaments so that thin filaments slide past actin and myosin lengthening in order to slide past each other the Z discs sliding over the myofilaments

actin and myosin sliding past each other and partially overlapping

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

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

Identify the correct sequence of the following events.a. Myosin generates a power stroke.b. Ca++ binds to troponin.c. ATP recharges the myosin head.d. Troponin removes tropomyosin from G actin.e. The sarcomere shortens.f. Myosin binds to actin. b, f, a, c, e, d f, a, c, e, d, b b, d, f, a, e, c e, c, a, b, d, f d, b, f, c, a, e a, b, c, d, e, f

b, : b. Ca++ binds to troponin. d: d. Troponin removes tropomyosin from G actin. f: f. Myosin binds to actin. a: a. Myosin generates a power stroke. e: e. The sarcomere shortens. c: c. ATP recharges the myosin head. The Ca++ binds to the troponin, which removes the tropomyosin from actin. This allows the myosin to bind to actin and generate a power stroke, shortening the sarcomere. ATP is used to recharge the myosin.

The influx of which ion is directly responsible for triggering the release of acetylcholine from a motor neuron? calcium glucose sodium potassium

calcium When an action potential from a neuron reaches an axon terminal, voltage-gated calcium channels open. The influx of calcium triggers exocytosis of acetylcholine.

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

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.

The sliding of the myofilaments is directly initiated by the availability of which chemical at the myofibril? acetylcholine potassium ions sodium ions calcium ions

calcium ions Calcium ions bind to the troponin-tropomyosin complex on actin. When calcium binds to troponin, a conformational shape change occurs in the protein complex, which results in the availability of the active sites on actin.

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

calcium ions 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.

A muscle fiber represents which organizational level of anatomy? organelle level organ level tissue level cellular level

cellular level Muscle fibers are simply muscle cells. But muscle cells are unique in many ways, and they are often very long, which is why they are described as fibers.

In an isotonic contraction, the muscle ________. rapidly resynthesizes creatine phosphate and ATP. changes in length and moves the "load". never converts pyruvate to lactate. does not change in length but increases tension.

changes in length and moves the "load"

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

chemically gated Na+-K+ 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

A muscle cell runs out of ATP. Even though these are cyclic reactions, what step of the cross bridge cycle given is most directly inhibited or terminated? the power stroke cocking of myosin head cross bridge formation cross bridge detachment

cross bridge detachment When ATP is added to the myosin, myosin detaches from actin.

Which of the following best describes the events of "contraction" in "excitation-contraction coupling"? cross bridge formation propagation of the action potential along the sarcolemma of the muscle fiber sliding of myofilaments release of calcium from the terminal cisternae

cross bridge formation

What is the type of chemical reaction used to rebuild ADP into ATP? dehydration synthesis hydrolysis rehydration synthesis

dehydration synthesis 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.

What event directly triggers the release of neurotransmitter shown in A? diffusion of K+ into the axon terminal diffusion of Ca2+ into the axon terminal diffusion of Na+ into the axon terminal diffusion of Na+ out of the axon terminal

diffusion of Ca2+ into the axon terminal A nerve impulse arrives at the axon terminal triggering the opening of Ca2+ channels, which allows for the diffusion of Ca2+ into the terminal. This in turn leads directly to the release of neurotransmitters by exocytosis.

Conduction of an action potential along the sarcolemma depends upon ___________. binding of acetylcholine to chemically gated channels shifting tropomyosin to uncover myosin binding sites release of calcium ions from the terminal cisterns diffusion of sodium ions through voltage-gated channels

diffusion of sodium ions through voltage-gated channels Action potentials are propagated along the sarcolemma by the sequential opening of voltage-gated sodium channels embedded in the membrane. As the initial set of sodium channels open, sodium ions diffuse inward, depolarizing the sarcolemma of the adjacent segment to threshold. This triggers the generation of the action potential at the new segment, and the process continues along the sarcolemma, conducting the action potential toward the t tubules.

The energy reserves for which of the ATP regenerating pathways will be depleted first during an extended period of light to moderate exercise? breakdown of stored glycogen. anaerobic glycolysis. direct phosphorylation of ADP by creatine phosphate. aerobic respiration.

direct phosphorylation of ADP by creatine phosphate This rapid ATP-synthesizing pathway only lasts for about 15 seconds.

The sliding filament model of contraction states that __________. 1. during contraction, the thin myofilaments slide past the thick myofilaments so that calcium ions can be released from the sarcoplasmic reticulum. 2. during contraction, the thin myofilaments slide past T tubules so that the Z discs are overlapping. 3. during contraction, the thin myofilaments slide past the thick myofilaments so that the actin and myosin myofilaments overlap to a greater degree. 4. during contraction, the thin myofilaments slide past the thick myofilaments so that the actin and myosin myofilaments no longer overlap.

during contraction, the thin myofilaments slide past the thick myofilaments so that the actin and myosin myofilaments overlap to a greater degree 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.

Where in the cross bridge cycle does ATP hydrolysis occur? during the cocking of the myosin head during the removal of calcium from troponin during the movement of tropomyosin to expose the active sites on actin during the power stroke

during the cocking of myosin head As ATP is broken down, its energy is used to cock the myosin head in preparation for the next power stroke.

A muscle that is lengthening while it produces tension is performing a(n) __________ contraction. concentric maximal eccentric isometric

eccentric During isotonic, eccentric contractions, muscle lengthens as it 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).

Although all the anatomical parts of muscle work together to give it its characteristics, which of the following proteins listed below would be most associated with the characteristics of extensibility? acetylcholine receptors in the motor end plate. thick (myosin) filaments. elastic (titin) filaments. potassium (K+) leak channels.

elastic (titin) filaments

What is the functional role of the T tubules? enhance cellular communication during muscle contraction hold cross bridges in place in a resting muscle synthesize ATP to provide energy for muscle contraction stabilize the G and F actin

enhance cellular communication during muscle contraction

Which membrane surrounds the others? endomysium exomysium epimysium perimysium

epimysium Epi means "over," "above," or "outer." Epimysium, therefore, is the outermost membrane.

What cellular event is indicated by A? exocytosis facilitated diffusion active transport endocytosis

exocytosis Neurotransmitters stored in synaptic vesicles are released into the synaptic cleft by exocytosis.

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

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

Action potentials travel the length of the axons of motor neurons to the axon terminals. These motor neurons __________. extend from the brain to the sarcolemma of a skeletal muscle fiber arise in the epimysium of a skeletal muscle and extend to individual skeletal muscle fibers extend from the spinal cord to the sarcolemma of a skeletal muscle fiber extend from the brain or spinal cord to the sarcolemma of a skeletal muscle fiber

extend from the brain or spinal cord to the sarcolemma of a skeletal muscle fiber Yes! The cell bodies of motor neurons to muscles in the head and neck are located in the brain. The cell bodies of motor neurons to the rest of our muscles are located in the spinal cord.

Skeletal muscle cells are grouped into bundles called __________. myofibrils myofilaments fascicles muscle fibers

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

Exhaustion of glycogen storage within a muscle fiber would have the biggest effect on ________. fast glycolytic fibers both slow and fast oxidative fibers slow oxidative fibers fast oxidative fibers

fast glycolytic fibers

Addition of more myoglobin to a muscle fiber would have the largest effect on ________. fast oxidative and slow oxidative fibers. fast oxidative fibers only. fast glycolytic fibers only. fast glycolytic and fast oxidative fibers.

fast oxidative and slow oxidative fibers

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

glycolysis 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 strongest muscle contractions are normally achieved by ________. a single stimulus above the threshold. increasing the stimulation up to the maximal stimulus. increasing stimulus above the threshold. recruiting small and medium muscle fibers.

increasing the stimulation up to the maximal stimulus

Immediately following the arrival of the stimulus at a skeletal muscle cell there is a short period called the ________ period during which the neurotransmitter is released by exocytosis, diffuses across the synaptic cleft, and binds to its receptors. relaxation contraction latent refractory

latent

Which of the following is the correct order for the phases of a muscle twitch? latent, relaxation, contraction. relaxation, contraction, latent. contraction, relaxation, latent. latent, contraction, relaxation.

latent, contraction, relaxation

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

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 structure most directly stimulates a skeletal muscle fiber to contract? Synaptic cleft Motor neuron Acetylcholinesterase Voltage-gated calcium channels

motor neuron The motor neuron transmits action potentials from the brain or spinal cord to muscle fibers by releasing acetylcholine at the neuromuscular junction.

Which of the following is the correct sequence of events for muscle contractions? muscle cell action potential, neurotransmitter release, ATP-driven power stroke, calcium ion release from SR, sliding of myofilaments motor neuron action potential, neurotransmitter release, muscle cell action potential, release of calcium ions from SR, ATP-driven power stroke, sliding of myofilaments neurotransmitter release, motor neuron action potential, muscle cell action potential, release of calcium ions from SR, ATP-driven power stroke neurotransmitter release, muscle cell action potential, motor neuron action potential, release of calcium ions from SR, sliding of myofilaments, ATP-driven power stroke

motor neuron action potential, neurotransmitter release, muscle cell action potential, release of calcium ions from SR, ATP-driven power stroke, sliding of myofilaments

The contractile units of skeletal muscles are ________. myofibrils T tubules mitochondria microtubules

myofibrils

Rigor mortis occurs because ________. sodium ions leak into the muscle causing continued contractions proteins are beginning to break down, thus preventing a flow of calcium ions no ATP is available to release attached actin and myosin molecules the cells are dead

no ATP is available to release attached actin and myosin molecules

Hypothetically, if a muscle were stretched to the point where thick and thin filaments no longer overlapped, ________. cross bridge attachment would be optimum because of all the free binding sites on actin no muscle tension could be generated maximum force production would result because the muscle has a maximum range of travel ATP consumption would increase because the sarcomere is "trying" to contract

no muscle tension could be generated

Duchenne muscular dystrophy could theoretically be cured if a technique was developed that would _________. strengthen the dystrophin proteins that are present in the patient's muscle fibers double the existing number of dystrophin molecules in the patient's muscle fibers strengthen the thick and thin filaments in the patient's muscle fibers none of the above

none of the above Duchenne muscular dystrophy is caused by a mutation in the dystrophin gene. Without a normal copy of DNA for transcription, there can never be a normal protein translated. This genetic mutation causes the protein to be either abnormal in structure or completely absent.

What chemical does NOT need to be present in the extracellular fluid for a signal to travel from neuron to muscle cell? potassium acetylcholine sodium calcium

potassium The potassium ion concentration is higher in the cytosol than in the extracellular fluid. Potassium ions are released during stimulation.

What is the primary function of wave summation? produce smooth, continuous muscle contraction prevent muscle fatigue increase muscle tension prevent muscle relaxation

produce smooth, continuous muscle contraction

Which of the following best describes the events of "excitation" in "excitation-contraction coupling"? cross bridge formation release of calcium from the terminal cisternae movement of tropomyosin away from the active sites on actin propagation of the action potential along the sarcolemma

propagation of the action potential along the sarcolemma "Excitation-contraction coupling" connects muscle fiber excitation to muscle fiber contraction. The action potential propagating along the sarcolemma represents the "excitation" of the muscle fiber. The ensuing cross bridge formation represents the "contraction" of the muscle fiber.

When a muscle is unable to respond to stimuli temporarily, it is in which of the following periods? refractory period fatigue period latent period relaxation period

refractory period

Which of the following events triggers the subsequent steps of excitation-contraction coupling? propagation of an action potential along the sarcolemma and T tubules binding of calcium ions to troponin, which removes the blocking action of tropomyosin release of acetylcholine from axon terminals at the neuromuscular junction release of calcium ions from the terminal cisterns of the sarcoplasmic reticulum

release of acetylcholine from axon terminals at the neuromuscular junction Release of acetylcholine from axon terminals at the neuromuscular junction is an event that precedes excitation-contraction coupling. Binding of acetylcholine to receptors in the motor end plate triggers an action potential that propagates along the sarcolemma and into the cell interior via T tubules.

Addition of more mitochondria to a muscle fiber will have the greatest effect on ________. both slow and fast oxidative fibers fast oxidative fibers fast glycolytic fibers slow oxidative fibers

slow oxidative fibers

If given the exact same amount of ATP, which of the three fiber types would be able to contract for the longest amount of time? fast glycolytic fibers both fast glycolytic and fast oxidative fibers slow oxidative fibers fast oxidative fibers

slow oxidative fibers

Unlike skeletal muscle, smooth muscle may spontaneously contract when it is stretched. What feature of smooth muscle allows it to stretch without immediately resulting in a strong contraction? low energy requirements smooth muscle tone slow, prolonged contractile activity stress-relaxation response

stress-relaxation response 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.

When a sarcomere contracts and thin filaments move over thick filaments you would expect to see ________. the I bands to appear wider the H zone to appear wider the I bands to appear smaller the A band to appear darker

the I bands to appear smaller

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

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.

Acetylcholine binds to its receptor in the sarcolemma and triggers __________. the opening of voltage-gated calcium channels the opening of calcium-release channels the opening of ligand-gated cation channels the opening of ligand-gated anion channels

the opening of ligand-gated cation channels Yes! These channels permit sodium ions to diffuse inward and potassium ions to diffuse outward.

Which of the following are composed of myosin? thick filaments intermediate filaments tropomyosin thin filaments

thick filaments Each thick filament is made of hundreds of myosin molecules.

The interaction between which protein and ion initiates muscle coupling? myosin; sodium ions. tropomyosin; calcium ions. troponin; sodium ions. troponin; calcium ions.

troponin; calcium ions When calcium ions bind to troponin, troponin changes shape and allows tropomyosin to shift away from its inhibitory position. As a result, myosin heads can bind to the actin molecules and begin the cross bridge cycle.