Anatomy and Physiology Ch 9
Which event causes cross bridge detachment? release of calcium from troponin release of ADP and inorganic phosphate from the myosin head nervous input ends ATP binding to the myosin head
ATP binding to myosin head As ATP binds, the myosin head releases from the active site on actin
Synaptic vesicles at the neuromuscular junction contain __________. acetylcholine ACh receptors calcium synaptic potentials
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.
Isometric contraction leads to movement of a load. True False
False An isometric contraction generates tension (force), but not enough to move the load. Overall muscle length does not change during iso(same) -metric(length) contractions. In contrast, isotonic contractions result in movement of the load.
In the muscles of the limbs, the origin usually lies proximal to the insertion. True False
True In the muscles of the limbs, the origin generally lies proximal to the insertion.
Isometric contractions are important contractions that allow humans to hold their posture over time. True False
True Muscle produces enough tension to support the skeleton, but not move it, creating the conditions for posture in humans.
Which organelle contains the contractile elements found in skeletal muscle? myofibril sarcolemma glycosome sarcoplasmic reticulum
myofibril The myofibrils contain the contractile elements of skeletal muscles, the sarcomeres. The sarcomeres contain even smaller rod-like structures called myofilaments.
Thick myofilaments are made of ________. myosin tropomyosin actin troponin
myosin Myosin, a contractile protein, is the principal component of the thick myofilaments.
Which selection correctly describes the role of calcium in coupling? Calcium binds to actin, which triggers it to bind to myosin. Calcium binds to actin, which triggers troponin to fall off and expose myosin-binding sites. 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.
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? Cross bridge detachment cannot occur. Detachment requires ATP, which is produced only during life. The cross bridge is locked up because ATP directly attaches myosin to actin. 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.
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.
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. Myosin heads would remain attached to actin, unable to detach. 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 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.
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 binds to calcium, causing muscle relaxation. Tropomyosin pushes the myosin head away, causing cross bridge detachment. 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. Tropomyosin covers active sites in relaxed muscle. When tropomyosin is displaced, the active sites are exposed for cross bridge formation.
Which pathway for regenerating ATP provides the majority of the energy used for muscle activity during 30 minutes of light to moderate exercise? use of stored ATP direct phosphorylation of ADP by creatine phosphate aerobic respiration anaerobic glycolysis
aerobic respiration Aerobic respiration occurs in the mitochondria, requires oxygen, and involves a sequence of chemical reactions in which bonds of fuel molecules are broken and the energy released is used to make ATP. Aerobic respiration provides a high yield of ATP for hours of low-to-moderate intensity muscle activity, whereas the other energy production processes provide energy for short duration (seconds to minutes) intense muscle activity.
Which of the following muscles is named for its size? trapezius sternocleidomastoid deltoid gluteus maximus
gluteus maximus The term maximus indicates the size of this muscle; gluteus maximus is the largest of the gluteus muscles. Additionally, gluteal is the name of the region where the muscle is located.
Which term best identifies a muscle cell? myofibril muscle fiber sarcomere muscle fascicle
muscle fiber Skeletal muscle cells fuse during development to form the mature, multinucleated muscle fibers.
Which selection best describes the initial event in contraction? 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. Calcium binds actin to myosin to begin the cross bridge cycle.
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.
Which muscle characteristic describes the ability of muscle to respond to a stimulus? elasticity contractility extensibility excitability
excitability Excitability, also termed responsiveness, is the ability to receive and respond to a stimulus, For example, skeletal muscle contracts in response to receiving chemical stimulation by a neurotransmitter called acetylcholine (ACh).
The longer a muscle is when it starts contracting, the more tension it can generate in the contraction. True False
False Maximum muscle contraction occurs in an intermediate range for the muscle where there is both a good number of cross bridges that can form and room for the sarcomere to shorten. If a muscle is too long, there will not be enough cross bridges that can form to generate tension.
What would happen if acetylcholine was not removed from the synaptic cleft? Voltage-gated Ca2+ channels would remain open. The acetylcholine receptors would not open. Multiple action potentials would occur in the muscle fiber. Multiple action potentials would occur in the motor neuron.
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.
Slow oxidative muscle fibers are best suited for ________. running a 100-yard dash lifting heavy weights at the gym hitting a baseball running a marathon
Running a marathon Slow oxidative muscle fibers are best suited for endurance activities, such as long distance running, cycling, or rowing.
How/when does the myosin head cock back to store energy for the next cycle? After the myosin head detaches, energy from ATP hydrolysis is used to re-cock the myosin head. The sliding of the actin myofilament during the power stroke re-cocks myosin heads that have previously delivered their power stroke. The power stroke cocks 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.
What is the role of calcium in the cross bridge cycle? Calcium binds to troponin, altering its shape. 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 active sites on actin, forming the cross bridge.
Calcium binds to troponin, altering its shape. Calcium binding to troponin causes tropomyosin to move away from the active sites on actin.
How do calcium ions initiate contraction in skeletal muscle fibers? Calcium ions bind to troponin, changing troponin's shape. Calcium ions bind to tropomyosin, exposing the active sites on actin. Calcium ion movement depolarizes the sarcolemma at the synaptic cleft. Calcium ions provide the energy necessary for the myosin head power stroke.
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 statements is NOT true regarding ATP production in muscles during periods of prolonged energy use, such as exercise? 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. In the absence of oxygen, anaerobic pathways provide minimal ATP regeneration for less than a minute. Prolonged activity requires the use of aerobic pathways for ATP regeneration. 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 ATO.
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? Hints It facilitates ACh's binding to the sarcolemma. It allows calcium to exit the sarcoplasmic reticulum and enter the cytosol. It permits calcium to exit the terminal cisternae and enter the T tubule. It allows calcium to exit the cytoplasm and enter the terminal cisternae.
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.
Which of the following is true concerning the anatomy of a skeletal muscle fiber? The sarcolemma is the muscle fiber's cytoplasm. A triad consists of a T tubule and the nearby sarcolemma. Myofibrils contain thick and thin filaments. T tubules are extensions of the sarcoplasmic reticulum.
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.
ACh receptors are found mainly in the __________. synaptic vesicles terminal cisternae sarcolemma axon terminal
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.
The __________ shorten(s) during muscle contraction thick filament sarcomere Z lines actin
Sarcomere As actin slides over myosin, the z lines are pulled closer together, shortening the sarcomere.
The calcium that initiates skeletal muscle contraction is released from what structure(s)? sarcolemma T tubules sarcomeres terminal cisternae
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.
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? The muscle would never contract. The muscle would be weaker than normal. The muscle tissues would never be able to relax. Actin will spontaneously fall apart.
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.
Which of the following statements is correct? Multipennate muscles do not produce much power because the fibers run in many directions. The number of muscle fibers best determines how powerful a muscle will be. Muscle fibers running in parallel arrangement generate more power. The more a muscle shortens, the more power it generates.
The number of muscle fibers best determines how powerful a muscle will be. More fibers means more power.
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.
Which of the following are composed of myosin? tropomyosin thin filaments thick filaments intermediate filaments
Thick filaments Each thick filament is made of hundreds of myosin molecules.
What event most directly triggers the release of calcium from the terminal cisternae? movement of tropomyosin away from the active sites on actin action potential propagating down the T tubule cross bridge formation between the thick and thin filaments action potential propagating toward the axon terminal
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.
Which functional group has the major responsibility for countering a specific movement? fixators antagonists synergists agonists
antagonists The antagonist opposes the movement produced by the agonist. It is often responsible for returning a limb to its initial position. Antagonists also adjust the action of their agonists by contracting slightly to provide some resistance, thus helping to prevent overshooting the mark or to slow or stop the movement. Agonist/antagonist pairs are located on opposite sides of the joint across which they act.
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. e, c, a, b, d, f a, b, c, d, e, f d, b, f , c, a, e f, a, c, e, d, b b, d, f, a, e, c b, f, a, c, e, d
b, d, f, a, e, c 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.
Proper application of RICE--rest, ice, compression, and elevation--can effectively control inflammation due to an ankle sprain. Why would compression provided by a correctly wrapped elastic Ace bandage be helpful in preventing further inflammation? because it promotes increased blood flow to the injury because it promotes fluid leakage into injured tissue because it reduces pain associated with joint injury because it immobilizes/stabilizes an injured ankle
because it immobilizes/stabilizes an injured ankle
What is the primary mechanism by which ACh is cleared from the synaptic cleft? broken down by acetylcholinesterase endocytosis by synaptic vesicles reuptake into the synaptic terminal diffusion away from the synaptic cleft
broken down by acetylcholinesterase 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.
Which of the following are correctly matched? convergent arrangement of fascicles; fan-shaped muscle parallel arrangement of fascicles; characteristic of sphincter muscles pennate arrangement of fascicles; spindle-shaped muscle circular arrangement of fascicles; describes the deltoid muscle
convergent arrangement of fascicles; fan-shaped muscle A convergent muscle has a broad origin, and its fascicles converge toward a single tendon of insertion. Such a muscle is triangular or fan shaped like the pectoralis major muscle of the anterior thorax.
Which of the following best describes the events of "contraction" in "excitation-contraction coupling"? cross bridge formation release of calcium from the terminal cisternae propagation of the action potential along the sarcolemma of the muscle fiber sliding of myofilaments
cross bridge formation "Excitation-contraction coupling" connects muscle fiber excitation to the muscle fiber contraction (cross bridge formation). During contraction, myosin heads form cross bridges many times—with each cross bridge generating a small amount of tension in the muscle fiber.
The distance between Z discs ________ during muscle contraction. decreases and then increases increases stays the same decreases
decreases During muscle contraction, the distance between Z discs decreases as the thin myofilaments slide across thick myofilaments, toward the M line in the center of each sarcomere. As the sarcomeres shorten, the myofibrils and, thus the myofibers shorten (contract).
Where in the cross bridge cycle does ATP hydrolysis occur? during the power stroke during the movement of tropomyosin to expose the active sites on actin during the cocking of the myosin head during the removal of calcium from troponin
during the cocking of the myosin head As ATP is broken down, its energy is used to cock the myosin head in preparation for the next power stroke.
When muscle cells break down glucose to generate ATP under oxygen deficient conditions, they will form ________. fatty acids glucose lactic acid glycogen
lactic acid Under anaerobic conditions, (oxygen deficient conditions) most of the pyruvic acid produced during glycolysis (breakdown of glucose) will be converted to lactic acid rather than enter the mitochondria to participate in aerobic respiration.
Which of the following muscles is named for its action? levator labii superioris gluteus minimus biceps brachii frontalis
levator labii superioris The levator labii superioris is named for its action of elevating the upper lip.
What, specifically, is a cross bridge? tropomyosin covering the active sites on actin myosin binding to actin ATP binding to the myosin head calcium binding to troponin
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.
Which of the following best describes the events of "excitation" in "excitation-contraction coupling"? propagation of the action potential along the sarcolemma release of calcium from the terminal cisternae movement of tropomyosin away from the active sites on actin cross bridge formation
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.
Which of the following movements demonstrates a first-class lever? lifting a rock with your right hand and arm raising your head up off your chest standing on your toes flexing your knee to raise your heel toward your buttocks
raising your head up off your chest Raising your head up off your chest demonstrates a first-class lever. The posterior neck muscles provide the effort, the atlanto-occipital joint is the fulcrum, and the weight to be lifted is the facial skeleton.
Which type of muscle CANNOT contract without being stimulated by the nervous system? smooth cardiac visceral skeletal
skeletal In order to contract, skeletal muscle fibers must be stimulated by the nervous system. The site of muscle stimulation, where the nerve fiber communicates with the muscle fiber, is called the neuromuscular junction.
Which of the following is CORRECTLY paired? smooth muscle: striated cardiac muscle: nonstriated cardiac muscle: voluntary control skeletal muscle: voluntary control
skeletal muscle: voluntary control Correct; skeletal muscle is under voluntary control.
A toxin released by certain bacteria can block the release of neurotransmitters into a neuromuscular synapse. What would result from such a block? The muscle would remain fixed at the length it was when the toxin contacted it. The muscle would become permanently contracted. the loss of ability to contract the muscle
the loss of the ability to contract the muscle Without acetylcholine, the muscle would not be able to contract or even maintain tone.
Which of the following is NOT used as a criterion for naming muscles? the number of origins for the muscle the location of the muscle the locations of the muscle attachments the nervous system's control of the muscle the shape of the muscle
the nervous system's control of the muscle Whether the muscle is controlled by the involuntary or voluntary nervous system is not a criterion used for naming muscles.
An enzyme known as acetylcholinesterase is present in the synaptic cleft. What is its role? to facilitate transport of acetylcholine across the cleft to facilitate the entrance of acetylcholine into the muscle cell to break down acetylcholine to pump Ca2+ back out of the axon terminal
to break down acetylcholine Acetylcholinesterase breaks acetylcholine apart, terminating the synaptic transmission. Choline can be taken back into the axon terminal and reused.
In muscle fibers, which regulatory protein blocks the attachment of myosin heads to actin? tropomyosin acetylcholinesterase thick filaments calcium
tropomyosin Tropomyosin covers the active site on actin, preventing cross bridge formation.
Which protein inhibits interaction between actin and myosin to prevent skeletal muscle contraction; and which ions remove the inhibition? actin; calcium ions tropomyosin; calcium ions troponin; sodium ions myosin; sodium ions
tropomyosin; calcium ions Tropomyosin, a regulatory protein, blocks the myosin binding sites on the actin molecules, preventing myosin heads from binding to actin to form cross bridges. When calcium ions bind to the TnC subunit of a troponin complex, troponin changes shape and moves tropomyosin away from its inhibitory position. As a result, the energized myosin heads (of thick myofilaments) can bind to the actin molecules (of thin myofilaments) and begin the cross bridge cycle, which shortens (contracts) the muscle fiber.
