MAP Chapter 10
The following is a list of the events that occur during a muscle contraction. What is the correct sequence of these events? 1. Myosin cross-bridges bind to the actin. 2. The free myosin head splits ATP. 3. Calcium ion is released from the sarcoplasmic reticulum. 4. The myosin head pivots toward the center of the sarcomere. 5. Calcium ion binds to troponin. 6. The myosin head binds an ATP molecule and detaches from the actin. 3, 5, 1, 2, 4, 6 5, 1, 4, 6, 2, 3 1, 3, 5, 4, 6, 2 3, 5, 1, 4, 6, 2 1, 4, 6, 2, 3, 5
3, 5, 1, 4, 6, 2
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 Calcium bound to troponin ATP bound to a myosin head Troponin bound to tropomyosin
A myosin head bound to actin
The characteristic muscle stiffness associated with rigor mortis is due to the inability of myosin filaments to detach from the active site on actin filaments. What molecule is essential for this detachment? ATP acetylcholine calcium acetylcholinesterase
ATP
After a power stroke, the myosin head must detach from actin before another power stroke can occur. What causes cross bridge detachment? Acetylcholine binds to receptors in the junctional folds of the sarcolemma. Calcium ions bind to troponin. ADP and inorganic phosphate are bound to the myosin head. ATP binds to the myosin head
ATP binds to the myosin head.
Tamara's muscle weakness and fatigue becomes progressively worse over the course of the day. This is a hallmark sign of myasthenia gravis, an autoimmune disorder that affects the ability of a motor neuron to communicate with a muscle fiber. What synaptic events must happen first for excitation to occur? Calcium binds to tropomyosin, shifting it from the active site on actin, allowing cross-bridge formation to occur as myosin binds to the active site. Acetylcholine is released from the axon terminal and diffuses across the synapse to bind to a receptor in the surface of the motor end plate. Sodium ions from the extracellular fluid diffuse into the cytosol of the muscle fiber, triggering the generation of an action potential in the sarcolemma. The action potential travels down the T tubules in the sarcolemma and triggers the release of calcium ions from the sarcoplasmic reticulum.
Acetylcholine is released from the axon terminal and diffuses across the synapse to bind to a receptor in the surface of the motor end plate.
The injection that dramatically improved Tamara's symptoms was Tensilon, an acetylcholinesterase inhibitor. What is acetylcholinesterase, and why was this injection effective in relieving Tamara's symptoms? -Acetylcholinesterase is a regulatory enzyme that inhibits the ACh receptors on the motor end plate. Inhibiting acetylcholinesterase improves muscle function because the ACh receptors are temporarily more active. -Acetylcholinesterase is the enzyme that clears acetylcholine from the synapse. Inhibiting this enzyme will enable acetylcholine to be available for a longer period to bind to receptors. -Acetylcholinesterase is an enzyme that degrades the ACh receptors. When acetylcholinesterase is inhibited, there are more receptors available for acetylcholine to bind, and muscle function improves. -Acetylcholinesterase is an acetylcholine antagonist that binds to motor end plate receptors and decreases the permeability of the sarcolemma to sodium. Inhibiting acetylcholinesterase increases the influx of sodium, leading to the generation of action potentials and an improvement in muscle function.
Acetylcholinesterase is the enzyme that clears acetylcholine from the synapse. Inhibiting this enzyme will enable acetylcholine to be available for a longer period to bind to receptors.
The binding of the neurotransmitter to receptors on the motor end plate causes which of the following to occur? -Binding causes chemically gated potassium channels to open in the motor end plate (junctional folds of the sarcolemma) and potassium 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. -Binding causes potassium voltage-gated 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.
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 transverse tubules. Calcium ions are stored in the mitochondria. Calcium ions are stored in the nuclei.
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.
When does cross bridge cycling end? 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 ions are passively transported back into the sarcoplasmic reticulum. Cross bridge cycling ends when calcium release channels in the sarcoplasmic reticulum open. 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.
How is delayed-onset muscle soreness (DOMS) different from muscle fatigue? -Delayed-onset muscle soreness occurs a day or more after the physical exertion. -There may be damage to the sarcolemma. -Muscle performance is impaired. -Delayed-onset muscle soreness involves pain.
Delayed-onset muscle soreness occurs a day or more after the physical exertion.
Myasthenia gravis is an autoimmune disorder that results in the production of antibodies that either block or cause the destruction of the ACh receptor. Why do you think that Tamara's symptoms become worse as the day progresses? -In the morning, the neuronal reserves of acetylcholine are larger, allowing for sufficient neurotransmitter release and resulting in effective muscle signaling. As the day progresses and the stores of acetylcholine become depleted, muscle function becomes progressively worse. -In myasthenia gravis the ACh receptors have a hyperaffinity to acetylcholine. After muscle activity, fatigue and weakness occur as fewer unbound receptors are available to bind acetylcholine. -As the muscle becomes fatigued over the course of the day's activities, the receptors bind less acetylcholine, which results in smaller and smaller action potentials being generated. Smaller action potentials mean weaker contractions, as seen by the increasing muscle weakness. -In the morning, the reserves of ATP are larger, allowing for sufficient acetylcholine release to overcome the unresponsive receptors. However, as the day progresses and stores of ATP become depleted, muscle function becomes progressively worse.
In the morning, the neuronal reserves of acetylcholine are larger, allowing for sufficient neurotransmitter release and resulting in effective muscle signaling. As the day progresses and the stores of acetylcholine become depleted, muscle function becomes progressively worse.
How would an elevated level of thyroid hormone in the body affect skeletal muscles? -It would stimulate atrophy. -It would stimulate hypertrophy. -It would stimulate energy use and heat production. -It would cause an increase in muscle mass. -It would decrease heat production by muscle tissue.
It would stimulate energy use and heat production.
Which of the following processes produces 36 ATP? -hydrolysis of creatine phosphate -Krebs cycle and oxidative phosphorylation -glycolysis
Krebs cycle and oxidative phosphorylation
What structure stimulates a skeletal muscle fiber to contract? Voltage-gated calcium channels. Synaptic cleft. Motor neuron. Acetylcholinesterase.
Motor neuron
The neuromuscular junction is a connection between a neuron and a __________. muscle fiber vesicle synaptic terminal myofibril
Muscle fiber
The "rest and recovery" period, where the muscle restores depleted reserves, includes all of the following processes EXCEPT __________. -Glycogen is synthesized from glucose molecules. -ATP is used to rephosphorylate creatine into creatine phosphate. -Pyruvic acid is converted back to lactic acid. -Oxygen rebinds to myoglobin.
Pyruvic acid is converted back to lactic acid.
Inadequate calcium in the neuromuscular junction would directly affect which of the following processes? Depolarization of the motor end plate by calcium influx Release of acetylcholine from the synaptic vesicles Breakdown of acetylcholine by acetylcholinesterase Conduction of action potentials by the motor neuron
Release of acetylcholine from the synaptic vesicles
The muscle action potentials that initiate contraction are transmitted from the sarcolemma into the interior of the muscle fiber by __________. the sarcoplasmic reticulum myofibrils myofilaments T tubules
T tubules
How does the myosin head obtain the energy required for activation? The energy comes from the hydrolysis of ATP. The energy comes from the hydrolysis of GTP. The energy comes from the direct phosphorylation of ADP by creatine phosphate. The energy comes from oxidative phophorylation.
The energy comes from the hydrolysis of ATP.
Malignant hyperthermia (MH) is a rare genetic disease in which the sarcoplasmic reticulum leaks calcium when the patient is put under general anesthesia. Which of the following best describes how anesthesia would affect the skeletal muscles of a patient with MH? -The muscles would contract because of calcium binding to troponin. -The muscles would contract because of increased nerve stimulation. -The muscles would relax because of calcium being pumped back into the sarcoplasmic reticulum. -The muscles would contract because of increased action potential generation in the sarcolemma.
The muscles would contract because of calcium binding to troponin
What happens immediately after the myosin head binds to the active site on actin? The myosin head pivots, moving the actin strand. ATP binds to the myosin head. The myosin head detaches from the active site on actin. Tropomyosin moves away from the active site on actin.
The myosin head pivots, moving the actin strand.
What structure is the functional unit of contraction in a skeletal muscle fiber? The junctional folds of the sarcolemma The sarcomere The triad The cross bridge
The sarcomere
Why do the disease tetanus and the normal sustained muscle contraction called tetanus share the same name? They both eliminate the relaxation phase in the affected muscle fibers. They both enable muscle fibers to reach near maximum tension. They are both brought on by bacterial infections. All of the listed responses are correct.
They both eliminate the relaxation phase in the affected muscle fibers.
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 prevents acetylcholine from being loaded into synaptic vesicles (vesamicol) -a drug that binds to the acetylcholine receptor and prevents it from opening (curare) -a drug that blocks the release of acetylcholine (botulinum toxin)
a drug that binds to and inactivates acetylcholinesterase (neostigmine)
In a neuromuscular junction, synaptic vesicles in the motor neuron contain which neurotransmitter? serotonin dopamine acetylcholine (ACh) norepinephrine
acetylcholine (ACh)
Triggering of the muscle action potential occurs after -calcium ion binds to channels on the motor end plate. -the action potential jumps across the neuromuscular junction. -acetylcholine binds to chemically-gated channels in the motor end plate. -acetylcholinesterase is released from synaptic vesicles into the synaptic cleft. -Any of these can produce an action potential in the muscle cell.
acetylcholine binds to chemically-gated channels in the motor end plate.
Which of the following situations could contribute to prolonged muscle contraction? infrequent neural stimulus acetylcholinesterase not being produced limited availability of calcium ions cross-bridge formation being reduced
acetylcholinesterase not being produced
A myosin head binds to which molecule to form a cross bridge? troponin actin tropomyosin
actin
Myosin molecules form cross-bridges when they attach to __________. calcium troponin tropomyosin actin
actin
Which of the following proteins contains the active site involved in cross-bridge formation? actin myosin troponin tropomyosin
actin
When a skeletal muscle fiber is at rest, its ATP demands are met by __________. glycolysis aerobic metabolism of glucose the breakdown of creatine phosphate aerobic metabolism of fatty acids
aerobic metabolism of fatty acids
During anaerobic glycolysis, ATP is produced. carbohydrate is metabolized. oxygen is not consumed. pyruvic acid is produced. All of the answers are correct.
all answers are correct
What causes the vesicles inside a neuron to fuse with the plasma membrane? -an action potential in the neuron -acetylcholine being broken down by acetylcholinesterase -an action potential in the muscle fiber -acetylcholine binding to acetylcholine receptors
an action potential in the neuron
What causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum within a muscle cell? arrival of an action potential calcium ion pump ATP troponin
arrival of an action potential
What causes the myosin head to disconnect from actin? binding of troponin binding of calcium binding of ATP hydrolysis of ATP
binding of ATP
The sarcoplasmic reticulum contains __________. myofilaments troponin T tubules calcium
calcium
Active sites on the actin become available for binding after myosin binds to troponin. troponin binds to tropomyosin. calcium binds to tropomyosin. calcium binds to troponin. actin binds to troponin.
calcium binds to troponin
Interactions between the thick and thin filaments are prevented by tropomyosin. To make the active sites accessible, __________ ions must bind to __________. calcium, troponin calcium, myosin calcium, actin sodium, troponin
calcium, troponin
When a muscle is stimulated repeatedly at a high rate, the amount of tension gradually increases to a steady maximum tension. This state of maximum tension is called complete tetanus. incomplete tetanus. wave summation. recruitment. a twitch
complete tetanus
What is the type of chemical reaction used to rebuild ADP into ATP? hydrolysis rehydration synthesis dehydration synthesis
dehydration synthesis
ATP binding leads to which of the following actions? Hints exposure of active sites on actin cross-bridge formation pivoting of the myosin head detaching and resetting cross-bridges
detaching and resetting cross-bridges
Titin is a(n) __________. tropomyosin-binding protein elastic protein thin-filament protein calcium-binding protein
elastic protein
What means of membrane transport is used to release the neurotransmitter into the synaptic cleft? exocytosis a channel a protein carrier
exocytosis
Activities involving eccentric contractions more commonly lead to delayed-onset muscle soreness than concentric or isometric contractions. Which of the following activities is thus a candidate for delayed-onset muscle soreness? flexion of the biceps brachii extension of the biceps brachii carrying a bowling ball pushing against the wall in the gym
extension of the biceps brachii
Inside a muscle, bundles of single muscle fibers form __________. thick filaments T tubules sarcomeres fascicles
fascicles
Muscles that move the eyeball have ________ fibers. slow circular fast intermediate All of the answers are correct.
fast
Large-diameter, densely packed myofibrils, large glycogen reserves, and few mitochondria are characteristics of intermediate fibers. fatty muscles. fast fibers. red muscles. slow fibers.
fast 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
Cardiac muscles cells have a sarcolemma that is more permeable to calcium, which causes them to __________. -form more cross-bridges -have faster contractions than skeletal muscle fibers -have contractions that last longer than skeletal muscle fibers -pump calcium back into the sarcoplasmic reticulum faster
have contractions that last longer than skeletal muscle fibers
Which of the following is not an effect of aging on the muscular system? exercise tolerance decreases decreased recovery from muscle injuries smaller muscle fibers hypertrophy muscles become less elastic
hypertrophy
Heat energy gained from muscle contraction is released by the ________ system. urinary endocrine respiratory cardiovascular integumentary
integumentary
Muscle fatigue occurs because of a buildup of __________ and a(n) __________ in pH. lactic acid; increase creatine phosphate; increase lactic acid; decrease creatine phosphate; decrease
lactic acid; decrease
Myofibrils are __________. bundles of muscle cells inside a whole muscle connections between actin and myosin made of a series of sarcomeres proteins that cover active sites on actin
made of a series of sarcomeres
Bacteria that cause tetanus release a neurotoxin. Which of the following components of the neuromuscular junction (NMJ) does this neurotoxin affect directly? sarcolemma epimysium myofilaments motor neurons
motor neurons
During the recovery period following exercise, all of the following are true except muscle fibers are unable to contract. heat is generated. oxygen is consumed at above the resting rate. lactic acid is removed from muscle cells. the muscle actively produces ATP.
muscle fibers are unable to contract
Which of the following is involved in the power stroke? Z lines tropomyosin myosin myofibrils
myosin
In the myofibril the thin filament is organized around a rod-like core protein called titin. actin. G actin. nebulin. myosin
nebulin
Acetylcholine receptors are primarily located __________. inside the muscle fiber on the motor end plate on the synaptic terminal inside vesicles
on the motor end plate
The ability of smooth muscle to function over a wide range of lengths is called variability. contractility. extensibility. elasticity. plasticity
plasticity
Which of these is NOT a function of smooth muscle? adjusting airway diameter elevating skin hairs churning the stomach contents pushing blood into the great vessels of the heart
pushing blood into the great vessels of the heart
What causes the power stroke? hydrolysis of ATP binding of ATP calcium release of ADP and Pi
release of ADP and Pi
The role of acetylcholinesterase in the neuromuscular junction is to __________. -remove acetylcholine from the synaptic cleft -release acetylcholine from the synaptic terminal -generate a muscle action potential -increase the sodium permeability of the motor end plate
remove acetylcholine from the synaptic cleft
After death, muscle fibers run out of ATP and calcium begins to leak from the sarcoplasmic reticulum into the sarcoplasm. This results in a condition known as depolarization. oxygen debt. tetany. treppe. rigor mortis.
rigor mortis
What happens to sarcomere length if the zone of overlap is decreased? (Figure 10-14) sarcomere length increases sarcomere length decreases sarcomere length stays the same
sarcomere length increases
Z lines define the edges of which of the following? myosin sarcomeres cross-bridges myofibrils
sarcomeres
Which organelle completely surrounds each myofibril inside a muscle fiber? nucleus calcium sarcoplasmic reticulum fascicle
sarcoplasmic reticulum
How is acetylcholine (ACh) removed from the synaptic cleft? -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 endocytosis into the muscle fiber
simple diffusion away from the synaptic cleft and acetylcholinesterase (AChE; an enzyme)
Which of the following types of muscle fibers are best adapted for prolonged contraction such as standing all day? fast fibers uninucleated fibers striated fibers slow fibers intermediate fibers
slow fibers
The end of a neuron, where acetylcholine-filled vesicles are located, is called the __________. synaptic cleft synaptic terminal motor end plate acetylcholine receptor
synaptic terminal
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? T tubule cytosol terminal cisterns (cisternae) of the sarcoplasmic reticulum sarcolemma
terminal cisterns (cisternae) of the sarcoplasmic reticulum
Which of the following most correctly describes excitation in the context of excitation-contraction coupling in skeletal muscle? -the release of calcium by the sarcoplasmic reticulum -the generation of an action potential in the sarcolemma -the formation of cross-bridges -the binding of calcium to troponin
the generation of an action potential in the sarcolemma
An action potential in the muscle fiber causes __________. Hints -the muscle fiber to contract -the release of acetylcholine into the synaptic cleft -acetylcholine to bind to receptors on the motor end plate -acetylcholinesterase to break down acetylcholine
the muscle fiber to contract
What is the synaptic cleft? -the region of the neuron containing synaptic vesicles -the space between the synaptic terminal and the motor end plate -the step where acetylcholinesterase (AChE) breaks down, or cleaves, acetylcholine -the border between the motor end plate and the sarcolemma
the space between the synaptic terminal and the motor end plate
Increased muscle fiber endurance can be produced by __________. the length of the muscle fiber a muscle fiber with a smaller diameter the amount of excitation-contraction coupling the type of activity performed
the type of activity performed
Myosin molecules form what part of the sarcomere? thick filament actin tropomyosin thin filament
thick filament
Which of the following phrases best describes how excitation is coupled to contraction in skeletal muscle fibers? -through calcium release from the sarcoplasmic reticulum -through electrical impulses -traveling along the sarcolemma -through T tubules -through cross-bridge formation
through calcium release from the sarcoplasmic reticulum
In the sarcomere which elastic protein attaches the thick filament to the Z line? titin actin G actin nebulin myosin
titin
The action potential is conducted into a skeletal muscle fiber by sarcoplasmic reticulum. motor end plates. triads. neuromuscular junctions. transverse tubules.
transverse tubules
T tubules and the terminal cisternae are clustered into structures called __________. sarcomeres myofibrils fascicles triads
triads
The protein that regulates muscle contraction by controlling the availability of active sites on actin is called actin. titin. myosin. tropomyosin. nebulin.
tropomyosin
When the sarcomere is at rest, what is covering the active sites on actin? troponin cross-bridges tropomyosin myosin
tropomyosin
Which of the following causes the active site on actin to be exposed or uncovered? tropomyosin shifting position calcium entering the sarcoplasmic reticulum cross-bridge formation troponin releasing calcium
tropomyosin shifting position
The binding of calcium to which molecule causes the myosin binding sites to be exposed? tropomyosin troponin actin myosin
troponin
To what regulatory protein does calcium bind during the initiation of the contraction cycle in skeletal muscle fibers? myosin actin troponin tropomyosin
troponin
When calcium is released inside a muscle cell, what does it bind to? tropomyosin actin myosin troponin
troponin
Inside a neuron, acetylcholine is contained within __________. acetylcholine receptors the motor end plate the synaptic cleft vesicles
vesicles
When an action potential arrives at the axon terminal of a motor neuron, which ion channels open? voltage-gated sodium channels voltage-gated potassium channels voltage-gated calcium channels chemically gated calcium channels
voltage-gated calcium channels
Which type of muscle fiber has a large quantity of glycogen and mainly uses glycolysis to synthesize ATP? white fast twitch fibers red slow twitch fibers
white fast twitch fibers
