physio ch12

Match from the following list. A. A band B. I band C. Z disk D. H zone E. M line The structures that serve as the attachment site for the thin filaments and mark the boundaries for one sarcomere. A band I band Z disk H zone M line

Z disk

Myasthenia gravis is a disease resulting from an autoimmune attack on the ACh receptors of the motor end plate. Binding of antibodies to the ACh receptors results in generalized muscle weakness that progresses as more ACh receptors are destroyed. Which of the following medications would help alleviate the muscle weakness? a drug that binds to and inactivates acetylcholinesterase (neostigmine) a drug that blocks the release of acetylcholine (botulinum toxin) a drug that binds to the acetylcholine receptor and prevents it from opening (curare) a drug that prevents acetylcholine from being loaded into synaptic vesicles (vesamicol)

a drug that binds to and inactivates acetylcholinesterase (neostigmine)

The nervous system avoids muscle fatigue during submaximal contraction by synchronous recruitment. always recruiting fast-twitch motor units. always recruiting slow-twitch motor units. asynchronous recruitment.

asynchronous recruitment.

The binding of acetylcholine to its receptor at the neuromuscular junction causes the opening of a channel for both Na+ and K+. Na+ channel. ryanodine receptor. calcium channel.

channel for both Na+ and K+.

As ATP binds to the myosin head at the beginning of a muscle contraction cycle, the myosin head immediately initiates binding with actin. detaches from actin. tightens its bond to actin. swivels.

detaches from actin.

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

during the cocking of the myosin head

Which fibers generate more force? slow-twitch fibers fast-twitch fibers

fast-twitch fibers

Motor units that control skeletal muscles involved with fine motor movements (eye muscles or the hands) have ________ muscle fibers than motor units that control more gross movements (gastrocnemius muscle of the lower leg). fewer more the same number of

fewer

In order for the bicep muscle to shorten, the force applied by the muscle must be ________ the load applied at the hand. equal to greater than less than

greater than

The force generated by a single muscle fiber can be increased by increasing frequency of action potentials and increasing muscle length beyond optimal only. increasing muscle length beyond optimal only. increasing frequency of action potentials only. increasing the asynchrony of recruitment only.

increasing frequency of action potentials only.

Within a single fiber, the tension developed during a twitch depends upon the duration of the stimulus. amplitude of the action potential. length of the sarcomeres prior to contraction. length of the thick filament.

length of the sarcomeres prior to contraction.

Which of the following is a characteristic of slow-twitch oxidative skeletal muscle fibers? long contraction duration only long contraction duration and high capillary density few mitochondria only long contraction duration, few mitochondria, and high capillary density high capillary density only

long contraction duration and high capillary density

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

A motor unit consists of one neuron and all the skeletal muscle fibers it controls. one skeletal muscle fiber and the neuron that controls that fiber. one skeletal muscle fiber and all the neurons that control that fiber. one axon terminal branch and the myofibrils it controls.

one neuron and all the skeletal muscle fibers it controls.

The function of transverse tubules is to store Ca2+ ions inside the muscle fiber. rapidly conduct action potentials to the interior of the muscle fiber. ensure a supply of glycogen throughout the muscle sarcoplasm. conduct ATP molecules out of the mitochondria throughout the sarcoplasm.

rapidly conduct action potentials to the interior of the muscle fiber.

The molecular event that occurs immediately after the power stroke is the hydrolysis of ATP by the myosin head. binding of actin to the myosin. binding of tropomyosin to the myosin. release of actin from the myosin head. release of ADP from the myosin.

release of ADP from the myosin.

The factor(s) that determine the duration of a twitch in various types of fibers is the speed of the hydrolysis of ATP only. removal of Ca2+ ions from the sarcoplasm and hydrolysis of ATP. removal of Ca2+ ions from the sarcoplasm only. movement of Na+ across their membranes only. removal of Ca2+ ions from the sarcoplasm and hydrolysis of ATP and movement of Na+ across their membranes.

removal of Ca2+ ions from the sarcoplasm only.

What immediately follows hydrolysis of ATP during muscle contraction? the power stroke rotation of the myosin head to the cocked position myosin binding to actin myosin release of actin

rotation of the myosin head to the cocked position

When a skeletal muscle cell contracts and the muscle shortens, the actin molecule swivels during the power stroke. some myosin heads are forming crossbridges as others are releasing them. the actin ATPase allows the actin molecule to swivel. the position of an actin molecule relative to a myosin molecule does not change. myosin heads generate a single power stroke.

some myosin heads are forming crossbridges as others are releasing them.

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

the opening of ligand-gated cation channels

Compared to fast-twitch glycolytic fibers (type IIb), slow-oxidative muscle fibers (type I) are characterized by a smaller diameter, less stored glycogen, and ________. a greater concentration of glycolytic enzymes faster reuptake of Ca2+ into the SR development of tension 2-3 times quicker the presence of myoglobin

the presence of myoglobin

A flexor is a skeletal muscle whose shortening moves attached bones away from one another. towards one another. laterally. medially

towards one another.

Put these events in the correct chronological sequence: 1. End-plate potentials trigger action potentials. 2. Transverse tubules convey potentials into the interior of the cell. 3. Acetylcholine binds to receptors on the motor end plate. 4. Ca2+ is released from the sarcoplasmic reticulum. 3, 1, 4, 2 2, 1, 4, 3 1, 2, 3, 4 4, 3, 2, 1 3, 1, 2, 4

3, 1, 2, 4

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

A myosin head bound to actin

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

A series of proteins that control calcium release.

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

ATP binding to the myosin head

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

ATP binds to the myosin head.

In order to contract and relax, muscle cells require energy in the form of ________. The immediate backup energy source is ________ that requires the enzyme ________. ATP, glucose, ATPase glucose, phosphocreatine, creatine kinase ATP, phosphocreatine, creatine kinase GTP, glucose, ATPase

ATP, phosphocreatine, creatine kinase

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 degraded by acetylcholinesterase. Acetylcholine is transported back into the axon terminal by a reuptake mechanism. Acetylcholine diffuses away from the cleft.

Acetylcholine is released by axon terminals of the motor neuron.

How/when does the myosin head cock back to store energy for the next cycle? The power stroke cocks the myosin head. when ADP is released from 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.

After the myosin head detaches, energy from ATP hydrolysis is used to re-cock the myosin head.

Skeletal muscle moves a bone at a joint, such as flexing the forearm at the elbow. How is the opposite action produced (i.e., extension at the elbow)? An antagonistic neuron secretes a different neurotransmitter onto the same muscle to produce the opposite skeletal movement. An antagonistic muscle produces the opposite movement. The muscle that produces flexion relaxes to produce extension. The muscle that produces flexion extends to produce extension.

An antagonistic muscle produces the opposite movement.

The relaxation of skeletal muscle relies on the activity of the ________, which decreases cytoplasmic calcium concentration. Ca2+ ATPase dihydropyridine (DHP) receptor (L-type calcium channel) ryanodine receptor acetylcholine receptor

Ca2+ ATPase

What is the role of calcium in the cross bridge cycle? 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 myosin, causing the myosin head to release from the actin myofilament.

Calcium binds to troponin, altering its shape.

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 sarcoplasmic reticulum. Calcium ions are stored in the nuclei. Calcium ions are stored in the mitochondria. Calcium ions are stored in the transverse tubules.

Calcium ions are stored in the sarcoplasmic reticulum.

What specific event triggers the uncovering of the myosin binding site on actin? Calcium ions bind to tropomyosin and change its shape. Calcium ions bind to troponin and change its shape. Sodium 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.

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

Calcium ions.

When comparing complete tetanus with unfused (incomplete) tetanus, which is true? Complete tetanus would occur when there is more time between twitch contractions. Complete tetanus involves some relaxation between twitches. Complete tetanus occurs at a lower frequency of stimulation than unfused tetanus. Complete tetanus involves development of maximum tension.

Complete tetanus involves development of maximum tension.

When does cross bridge cycling end? Cross bridge cycling ends when ATP binds to the myosin head. 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.

Cross bridge cycling ends when sufficient calcium has been actively transported back into the sarcoplasmic reticulum to allow calcium to unbind from troponin.

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 refers to the release of calcium ions from the sarcoplasmic reticulum. Excitation refers to the shape change that occurs in voltage-sensitive proteins in the sarcolemma. 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.

Excitation, in this case, refers to the propagation of action potentials along the sarcolemma.

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 attached to actin, unable to detach. Myosin heads would remain detached, unable to cock. Myosin heads would remain attached to actin, unable to perform the power stroke. Tropomyosin would not move, and the active sites on actin would not be exposed.

Myosin heads would remain detached, unable to cock.

What is it called when myosin crossbridges attach to actin filaments and pull them toward the middle of the sarcomere? Rotational pulling Filamental sliding Power stroke Pull flash

Power stroke

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

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

The displacement of tropomyosin exposes the active sites of actin, allowing cross bridges to form.

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

The energy comes from the hydrolysis of ATP.

What structure is the functional unit of contraction in a skeletal muscle fiber? View Available Hint(s) The triad The cross bridge The sarcomere The junctional folds of the sarcolemma

The sarcomere

During contraction, what prevents actin myofilaments from sliding backward when a myosin head releases? The cross bridge remains in place, preventing the actin myofilament from sliding. There are always some myosin heads attached to the actin myofilament when other myosin heads are detaching. 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.

Which of the following occurs when a myofibril contracts? Thin and thick filaments contract as they slide past each other. Thin and thick filaments slide past each other, but do not change in length. Thin filaments contract, but thick filaments slide. Thick filaments contract, but thin filaments slide.

Thin and thick filaments slide past each other, but do not change in length.

What happens when calcium binds troponin? Troponin changes shape and covers the SR calcium channel, a form of negative feedback. Troponin releases myosin and activates actin. Tropomyosin is pulled away from the actin active site. Troponin binds to actin and causes sarcomere shortening.

Tropomyosin is pulled away from the actin active site.

How does troponin facilitate cross bridge formation? Troponin hydrolyzes ATP, which provides the energy necessary for cross bridges to form. 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 gathers excess calcium that might otherwise block actin's progress.

Troponin controls the position of tropomyosin on the thin filament, enabling myosin heads to bind to the active sites on actin.