Ch.9 Muscular System
The bond between the actin and myosin head weakens as a result of ______.
ATP
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. -Calcium ions bind to troponin. -Acetylcholine binds to receptors in the junctional folds of the sarcolemma. -ADP and inorganic phosphate are bound to the myosin head.
ATP binds to the myosin head.
neurotransmitter that stimulates skeletal muscle contraction.
Acetylcholine
binds to ACh receptors, causing them to open chemically gated ion channels.
ACh
protein embedded in the sarcolemma
ACh receptor
is not bound to myosin during the detachment step
ADP
Molecule(s) bound to the myosin head at the start of the cross bridge cycle
ADP and Pi
The molecules released just before power stroke
ADP and Pi
myofilament stiffened and stabilized by tropomyosin
Actin
: Activates synaptic vesicles in axon terminals to fuse with plasma membrane of axon terminal.
Calcium ions
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 mitochondria. -Calcium ions are stored in the sarcoplasmic reticulum. -Calcium ions are stored in the nuclei. -Calcium ions are stored in the transverse tubules.
Calcium ions are stored in the sarcoplasmic reticulum.
diffuses out of the muscle fiber through open chemically gated ion channels.
K+
Which of the following is true concerning the anatomy of a skeletal muscle fiber? -Myofibrils contain thick and thin filaments. -T tubules are extensions of the sarcoplasmic reticulum. -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.
The end plate potential is primarily, and most directly, caused by the movement of ______.
Na+
diffuses into the muscle fiber through open chemically gated ion channels.
Na+
It diffuses across the cell membrane resulting in depolarization.
Sodium ions
A structure that forms a path from the membrane to the cell interior
T tubule
Cduct(s) action potentials throughout the interior of the muscle fiber.
T tubule
Continued sustained smooth contraction due to rapid stimulation.
Tetanus
What structure is the functional unit of contraction in a skeletal muscle fiber? -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. -The actin myofilament can only move in one direction relative to the myosin filament. -There are always some myosin heads attached to the actin myofilament when other myosin heads are detaching. -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 describes the cells of unitary smooth muscle? -They are used for vision and hair raising. -They depend upon recruitment using the autonomic nervous system. -They exhibit spontaneous action potentials. -They consist of muscle fibers that are structurally independent of each other.
They exhibit spontaneous action potentials.
______ has an affinity for myosin binding sites in the absence of calcium.
Tropomyosin
A protein that changes shape as a direct result of an action potential
Voltage-sensitive tubule protein
Which description is most appropriate for a myofibril? -a single long, thin organelle containing many proteins -a single long protein structure found in the sarcomeres of a muscle cell -a single long cell found within a muscle -a single group of long muscle cells surrounded by a membrane
a single long, thin organelle containing many proteins
Synaptic vesicles at the neuromuscular junction contain __________. -ACh receptors -synaptic potentials -calcium -acetylcholine
acetylcholine
A myosin head binds to which molecule to form a cross bridge? -troponin -actin -tropomyosin
actin
The sliding filament model of contraction involves ________. -actin and myosin sliding past each other and partially overlapping -the Z discs sliding over the myofilaments -actin and myosin lengthening in order to slide past each other -the shortening of thick filaments so that thin filaments slide past
actin and myosin sliding past each other and partially overlapping
Actin status to begin cross bridge formation
actin-binding sites exposed
What causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum within a muscle cell? -arrival of an action potential -ATP -calcium ion pump -troponin
arrival of an action potential
The influx of which ion is directly responsible for triggering the release of acetylcholine from a motor neuron? -calcium -potassium -sodium -glucose
calcium
What is the type of chemical reaction used to rebuild ADP into ATP? -rehydration synthesis -hydrolysis -dehydration synthesis
dehydration synthesis
Where in the cross bridge cycle does ATP hydrolysis occur? -during the movement of tropomyosin to expose the active sites on actin -during the removal of calcium from troponin -during the cocking of the myosin head -during the power stroke
during the cocking of the myosin head
Skeletal muscle cells are grouped into bundles called __________. -myofilaments -muscle fibers -fascicles -myofibrils
fascicles
Exhaustion of glycogen storage within a muscle fiber would have the biggest effect on ________. -fast glycolytic fibers -both slow and fast oxidative fibers -fast oxidative fibers -slow 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 glycolytic fibers only -fast oxidative fibers only -fast glycolytic and fast oxidative fibers
fast oxidative and slow oxidative fibers
An anaerobic metabolic pathway that results in the production of two net ATPs per glucose plus two pyruvic acid molecules is ________. -the electron transport chain -glycolysis -the citric acid cycle -hydrolysis
glycolysis
Which of the following processes produces molecules of ATP and has two pyruvic acid molecules as end products? -hydrolysis of creatine phosphate -Krebs cycle and oxidative phosphorylation -glycolysis
glycolysis
The strongest muscle contractions are normally achieved by ________. -increasing the stimulation up to the maximal stimulus -increasing stimulus above the threshold -a single stimulus above the threshold -recruiting small and medium muscle fibers
increasing the stimulation up to the maximal stimulus
During an exercise where muscles do not shorten, _______ contractions have occurred.
isometric
When muscle tension develops but the load is not moved.
isometric contraction
portion of sarcolemma containing ACh receptors
junctional folds
Which of the following is the correct order for the phases of a muscle twitch? -relaxation, contraction, latent -latent, contraction, relaxation -latent, relaxation, contraction -contraction, relaxation, latent
latent, contraction, relaxation
Which of the following is a factor that affects the velocity and duration of muscle contraction? -number of muscle fibers stimulated -size of the muscle fibers stimulated -load on the fiber -muscle length
load on the fiber
Made up of several sarcomeres
myofibrils
myofilament with a knob-like head
myosin
Rigor mortis occurs because ________. -the cells are dead -proteins are beginning to break down, thus preventing a flow of calcium ions -no ATP is available to release attached actin and myosin molecules -sodium ions leak into the muscle causing continued contractions
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, ________. -maximum force production would result because the muscle has a maximum range of travel -cross bridge attachment would be optimum because of all the free binding sites on actin -ATP consumption would increase because the sarcomere is "trying" to contract -no muscle tension could be generated
no muscle tension could be generated
Only ______ , of the myosin heads are detached from actin at any one time while calcium is present and cycling continues.
one-half
The __________ shorten(s) during muscle contraction -sarcomere -actin -Z lines -thick filament
sarcomere
How is acetylcholine (ACh) removed from the synaptic cleft? -acetylcholinesterase (AChE; an enzyme) and endocytosis into the muscle fiber -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) -acetylcholinesterase (AChE; an enzyme) only
simple diffusion away from the synaptic cleft and acetylcholinesterase (AChE; an enzyme)
long, cylindrical cells
skeletal muscle fibers
Reduction in blood flow to a muscle fiber would have the greatest effect on ________. -both slow and fast oxidative -slow oxidative fibers -fast glycolytic -fast oxidative fibers
slow oxidative fibers
Which muscle fiber type is best suited for endurance activities, such as long-distance jogging? -slow oxidative fibers -slow glycolytic fibers -fast glycolytic fibers -fast oxidative fibers
slow oxidative fibers
container of many neurotransmitter molecules
synaptic vesicle
release(s) calcium ions into the sarcoplasm.
terminal cistern
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
Which of the following are composed of myosin? -thin filaments -intermediate filaments -thick filaments -tropomyosin
thick filaments
What is name given to the regularly spaced infoldings of the sarcolemma? -transverse or T tubules -motor endplates -sarcoplasmic reticulum -terminal cisternae
transverse or T tubules
The final chemical messenger and "trigger" for muscle contraction. It binds to troponin.
Calcium ions
What is the relationship between the number of motor neurons recruited and the number of skeletal muscle fibers innervated? -A skeletal muscle fiber is innervated by multiple motor neurons. -Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron. -Motor neurons always innervate thousands of skeletal muscle fibers. -A motor neuron typically innervates only one skeletal muscle fiber.
Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron.
Acetylcholine receptors are best characterized as what type of channel? -chemically gated Ca2+ channels -chemically gated Na+-K+ channels -voltage-gated Na+-K+ channels -voltage-gated Ca2+ channels
chemically gated Na+-K+ channels
Location of higher concentration of Ca2+ needed for cross bridge formation and cycling
cytoplasm
Conduction of an action potential along the sarcolemma depends upon ___________. -shifting tropomyosin to uncover myosin binding sites -diffusion of sodium ions through voltage-gated channels -release of calcium ions from the terminal cisterns -binding of acetylcholine to chemically gated channels
diffusion of sodium ions through voltage-gated channels
receive(s) stimulus from the motor neuron.
junctional folds
The contractile units of skeletal muscles are ________. -mitochondria -T tubules -microtubules -myofibrils
myofibrils
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
Myosin head energy status during the power stroke
pivots and returns to low energy
What chemical does NOT need to be present in the extracellular fluid for a signal to travel from neuron to muscle cell? -potassium -calcium -acetylcholine -sodium
potassium
Which of the following events triggers the subsequent steps of excitation-contraction coupling? -propagation of an action potential along the sarcolemma and T tubules -release of calcium ions from the terminal cisterns of the sarcoplasmic reticulum -release of acetylcholine from axon terminals at the neuromuscular junction -binding of calcium ions to troponin, which removes the blocking action of tropomyosin
release of acetylcholine from axon terminals at the neuromuscular junction
Slow oxidative muscle fibers are best suited for __________. -hitting a baseball -running a 100-yard dash -lifting heavy weights at the gym -running a marathon
running a marathon
Addition of more mitochondria to a muscle fiber will have the greatest effect on ________. -both slow and fast oxidative fibers -slow oxidative fibers -fast oxidative fibers -fast glycolytic 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? -both fast glycolytic and fast oxidative fibers -fast oxidative fibers -fast glycolytic fibers -slow oxidative fibers
slow oxidative fibers
When the chemically gated ion channels open, which ion is mainly responsible for depolarizing the sarcolemma? -calcium -sodium -ACh -potassium
sodium
Myoglobin ________. -breaks down glycogen -stores oxygen in muscle cells -produces the end plate potential -is a protein involved in the direct phosphorylation of ADP
stores oxygen in muscle cells
The calcium that initiates skeletal muscle contraction is released from what structure(s)? -T tubules -sarcolemma -terminal cisternae -sarcomeres
terminal cisternae
change(s) shape upon binding with calcium ions.
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, 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 release of calcium ions from the sarcoplasmic reticulum. -Excitation refers to the shape change that occurs in voltage-sensitive proteins in the sarcolemma.
Excitation, in this case, refers to the propagation of action potentials along the sarcolemma.
bundle of skeletal muscle fibers enclosed by connective tissue called perimysium
Fascicle
When the muscle tension developed overcomes the load and muscle shortening occurs.
Isotonic contraction
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 facilitates ACh's binding to the sarcolemma. -It allows calcium to exit the sarcoplasmic reticulum and enter the cytosol. -It allows calcium to exit the cytoplasm and enter the cisterns.
It allows calcium to exit the sarcoplasmic reticulum and enter the cytosol.
Where the axon of a motor neuron connects with the muscle fibers.
Neuromuscular junction
The cross bridge cycle starts when _________. -ATP binds to troponin and is hydrolyzed to ADP and Pi -Ca2+ 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
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 myosin, causing the myosin head to release from the actin myofilament. -Calcium binds to troponin, exposing the active site on troponin.
Calcium binds to troponin, altering its shape.
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 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.
Calcium binds to troponin, which moves tropomyosin and exposes the myosin-binding sites on actin.
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
Which of the following choices best summarizes excitation-contraction coupling? -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 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 an electrical stimulus is conveyed to a muscle fiber to enact contraction
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. -Myosin cross-bridge binding sites. -Voltage-gated sodium channels. -Potassium leak channels.
A series of proteins that control calcium release.
A neurotransmitter released at motor end plates by the axon terminals.
Acetylcholine
enzyme located in the synaptic cleft that breaks down acetylcholine.
Acetylcholinesterase
Which of the following best describes the role of acetylcholinesterase molecules at the neuromuscular junction? -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. -Acetylcholinesterase binds ACh, preventing it from binding to chemically gated ion channels. -Acetylcholinesterase prevents Na+ and K+ from passing through chemically gated ion channels.
Acetylcholinesterase breaks down ACh, which allows chemically gated ion channels to close.
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 is directly reabsorbed into the axon terminal for reuse. -Ach passes down the T tubules and triggers the release of calcium from the sarcoplasmic reticulum.
Ach is broken down by acetylcholinesterase.
How/when does the myosin head cock back to store energy for the next cycle? -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.
After the myosin head detaches, energy from ATP hydrolysis is used to re-cock the myosin head.
Which of the following is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers? -Action potentials. -Calcium ions. -Sodium ions. -Acetylcholine.
Calcium ions.
Which of the following is NOT a role of ATP in muscle contraction? -Transporting calcium ions into the sarcoplasmic reticulum -Exposing myosin binding sites on actin -Detaching the cross bridge from actin Energizing the power stroke of the cross bridge
Exposing 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? -Prolonged activity requires the use of aerobic pathways for ATP regeneration. -In the absence of oxygen, anaerobic pathways provide minimal ATP regeneration for less than a minute. -In the absence of oxygen, creatine phosphate can drive aerobic respiration pathways for a few minutes. -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, creatine phosphate can drive aerobic respiration pathways for a few minutes.
If the cell could no longer produce ATP, what would be the effect on the sarcoplasmic reticulum? -It would be unable to concentrate Ca++ in the sarcoplasmic reticulum. -The muscle would not contract. -Ca++ would leak out of the cell. -Ca++ would build up in the sarcoplasmic reticulum.
It would be unable to concentrate Ca++ in the sarcoplasmic reticulum.
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 the junctional folds from triggering an action potential. -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 myosin from forming cross bridges with actin.
ion entering muscle fiber through open chemically gated ion channels
Na+
he "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. -Oxygen rebinds to myoglobin. -Glycogen is synthesized from glucose molecules. -Pyruvic acid is converted back to lactic acid.
Pyruvic acid is converted back to lactic acid.
What role does tropomyosin play in the cross bridge cycle? -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 binds to calcium, causing muscle relaxation. -Tropomyosin pushes the myosin head away, causing cross bridge detachment.
The displacement of tropomyosin exposes the active sites of actin, allowing cross bridges to form.
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? -The first statement is true; the second statement is false. -Both statements are true. -The first statement is false; the second statement is true. -Both of these statements are false.
The first statement is true; the second statement is false.
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? -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' 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.
The runners' use of stored oxygen, glucose, and creatine phosphate is being replenished and this requires a prolonged increase of oxygen intake.
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 action potential stops going down the overloaded T tubules -calcium ions returning to the terminal cisternae -acetylcholinesterase breaks apart the ACh -the tropomyosin blocking the myosin once full contraction is achieved
acetylcholinesterase breaks apart the ACh
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 -action potential propagating toward the axon terminal -cross bridge formation between the thick and thin filaments
action potential propagating down the T tubule
What means of membrane transport is used to release the neurotransmitter into the synaptic cleft? -a protein carrier -a channel -exocytosis
exocytosis
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. -contraction -relaxation -latent -refractory
latent
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
What is the primary function of wave summation? -prevent muscle relaxation -produce smooth, continuous muscle contraction -prevent muscle fatigue -increase muscle tension
produce smooth, continuous muscle contraction
Which of the following best describes the events of "excitation" in "excitation-contraction coupling"? -propagation of the action potential along the sarcolemma -cross bridge formation -movement of tropomyosin away from the active sites on actin -release of calcium from the terminal cisternae
propagation of the action potential along the sarcolemma
Actin behavior during the power stroke
ratchets toward the M line
membrane of muscle cell
sarcolemma
membrane surrounding muscle fiber
sarcolemma
the cytoplasm of a skeletal muscle fiber
sarcoplasm
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? -slow, prolonged contractile activity -stress-relaxation response -low energy requirements -smooth muscle tone
stress-relaxation response
the space between the axon terminal and junctional folds.
synaptic cleft
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? -sarcolemma -cytosol -T tubule -terminal cisterns (cisternae) of the sarcoplasmic reticulum
terminal cisterns (cisternae) of the sarcoplasmic reticulum
When a sarcomere contracts and thin filaments move over thick filaments you would expect to see ________. -the H zone to appear wider -the I bands to appear smaller -the A band to appear darker -the I bands to appear wider
the I bands to appear smaller
An action potential is propagated down the sarcolemma as a result of which of the following? -the opening of voltage-gated sodium channels -the closing of potassium channels -the closing of voltage-gated sodium channels -the opening of voltage-gated potassium channels
the opening of voltage-gated sodium channels
The contractile, or functional, unit of a muscle fiber is __________. the elastic filament -troponin -the sarcomere -the myofilament
the sarcomere
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? -elastic (titin) filaments -potassium (K+) leak channels -thick (myosin) filaments -voltage gated sodium channels
thick (myosin) filaments
The binding of calcium to which molecule causes the myosin binding sites to be exposed? -myosin -actin -troponin -tropomyosin
troponin
The protein that binds calcium
troponin
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
Inadequate calcium in the neuromuscular junction would directly affect which of the following processes? -Depolarization of the junctional folds -Conduction of action potentials by the motor neuron -Breakdown of acetylcholine by acetylcholinesterase -Release of acetylcholine from the synaptic vesicles
-Release of acetylcholine from the synaptic vesicles
neurotransmitter at neuromuscular junction
ACh
Which of the following best describes how ACh changes the ion permeability of the sarcolemma? -ACh entry into the axon terminal causes neurotransmitter release. -ACh binds to receptors in the junctional folds. -ACh entry into the muscle fiber causes Ca2+ to be released by the sarcoplasmic reticulum. -ACh activates acetylcholinesterase.
ACh binds to receptors in the junctional folds.
Which event causes cross bridge detachment? -ATP binding to the myosin head -release of calcium from troponin -release of ADP and inorganic phosphate from the myosin head -nervous input ends
ATP binding to the myosin head
Which of the following occurs during cross bridge cycling? -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. -The troponin-tropomyosin complex blocks the active sites on actin. -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.
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 degraded by acetylcholinesterase. -Acetylcholine is transported back into the axon terminal by a reuptake mechanism. -Acetylcholine diffuses away from the cleft. -Acetylcholine is transported into the postsynaptic neuron by receptor-mediated endocytosis.
Acetylcholine is degraded by acetylcholinesterase.
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 is released by axon terminals of the motor neuron. -Acetylcholine binds to its receptor in the junctional folds of the sarcolemma. Its receptor is linked to a G 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 and moves across the synaptic cleft bound to a transport protein.
Acetylcholine is released by axon terminals of the motor neuron.
a type of chemically-gated ion channel located on the junctional folds of the muscle fiber.
Acetylcholine receptor
Breaks down ACh into its building blocks, rendering it inactive.
Acetylcholinesterase
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? -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. -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 to sarcolemma receptors initiates graded potentials.
What causes the release of calcium ions into the sarcoplasm from the terminal cisterns? -The binding of myosin heads to actin -The change in the shape of troponin -Acetylcholine entering the sarcoplasm of the muscle fiber -An action potential traveling along the t tubule
An action potential traveling along the t tubule
What action is directly responsible for the generation of an action potential at the sarcolemma? -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. -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.
he 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 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 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.
Which of the following is most directly required to initiate the coupling of myosin to actin? -ACh -Ca++ -glucose -ATP
Ca++
ion triggering exocytosis
Ca2+
The swollen chamber of an organelle that lies on either side of a T tubule
Cistern
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. -ATP binds to the myosin head to cause cross bridge detachment. -Calcium ions are removed from the sarcoplasm by active transport.
Calcium ions are removed from the sarcoplasm by active transport.
What specific event triggers the uncovering of the myosin binding site on actin? -Calcium release channels open in the sarcoplasmic reticulum, and calcium levels rise in the sarcoplasm. -Sodium ions bind to troponin and change its shape. -Calcium ions bind to troponin and change its shape. -Calcium ions bind to tropomyosin and change its shape.
Calcium ions bind to troponin and change its shape.
How do calcium ions initiate contraction in skeletal muscle fibers? -Calcium ions bind to troponin, changing troponin's shape. -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 tropomyosin, exposing the active sites on actin.
Calcium ions bind to troponin, changing troponin's shape.
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. -Sodium release from the sarcoplasmic reticulum initiates the contraction. -Action potentials propagate into the interior of the skeletal muscle fiber. -Calcium release from the sarcoplasmic reticulum initiates the contraction.
Calcium release from the sarcoplasmic reticulum initiates the 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 has well-developed T tubules at the site of invagination. -Certain smooth muscle cells can actually divide to increase their numbers. -Smooth muscle cannot stretch as much as skeletal muscle.
Certain smooth muscle cells can actually divide to increase their numbers.
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.
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 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. -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.
______ is a missing protein in Duschenne 19s muscular dystrophy.
Dystrophin
Which of the following processes produces 36 ATP? -Krebs cycle and oxidative phosphorylation -glycolysis -hydrolysis of creatine phosphate
Krebs cycle and oxidative phosphorylation
What structure most directly stimulates a skeletal muscle fiber to contract? -Motor neuron -Synaptic cleft -Voltage-gated calcium channels -Acetylcholinesterase
Motor neuron
What would happen if acetylcholine was not removed from the synaptic cleft? -The acetylcholine receptors would not open. -Voltage-gated Ca2+ channels would remain 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.
Determined by alternating motor units of a muscle organ even when the muscle is at rest.
Muscle tone
Which selection best describes the initial event in contraction? -The myofilaments slide closer together. -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. -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.
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.
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 attaches troponin to actin. -One subunit binds to potassium ions. -One subunit binds tropomyosin and helps position it on actin. -One subunit binds to calcium ions.
One subunit binds to potassium ions.
Of the following items listed below, which is the best description for why skeletal muscle stores glycogen? -Glycogen provides a smooth surface for filaments to slide on. -The glycogen is an insulating layer that helps regulate body temperature. -Skeletal muscle is a heavy consumer of energy. -Glycogen is part of muscles rigid supporting framework.
Skeletal muscle is a heavy consumer of energy.
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. -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.
Synaptic vesicles fuse to the plasma membrane of the axon terminal and release acetylcholine.
How does the myosin head obtain the energy required for activation? -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.
The energy comes from the hydrolysis of ATP.
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. Sodium ions diffuse inward along favorable chemical and electrical gradients. -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. Potassium ions diffuse outward 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 inside surface of the sarcolemma is negatively charged compared to the outside surface. Sodium ions diffuse inward along favorable chemical and electrical gradients.
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. -Actin will spontaneously fall apart. -The muscle would be weaker than normal. -The muscle tissues would never be able to relax.
The muscle tissues would never be able to relax.
If troponin is a component of both cardiac and skeletal muscle, why is an elevated plasma troponin level useful in diagnosing myocardial damage? -Whenever cardiac muscle is damaged, skeletal muscles receive inadequate blood flow and release troponin. -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. -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.
Which of the following best describes the role of muscle fiber triads? -Two axon terminals and the one muscle fiber they activate compose a functional neuromuscular triad, or the functional unit of muscle. -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. -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.
What is the role of tropomyosin in skeletal muscles? -Tropomyosin serves as a contraction inhibitor by blocking the myosin binding sites on the actin molecules. -Tropomyosin is the receptor for the motor neuron neurotransmitter. -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 moves away from the active sites on actin, permitting cross bridge formation. -Troponin hydrolyzes ATP, which provides the energy necessary for cross bridges to form. -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.
Muscle tone is ________. -the ability of a muscle to efficiently cause skeletal movements -the feeling of well-being following exercise -the condition of athletes after intensive training -a state of sustained partial contraction
a state of sustained partial contraction
In a neuromuscular junction, synaptic vesicles in the motor neuron contain which neurotransmitter? -norepinephrine -acetylcholine (ACh) -dopamine -serotonin
acetylcholine (ACh)
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
What causes the myosin head to disconnect from actin? -binding of troponin -binding of calcium -binding of ATP -hydrolysis of ATP
binding of ATP
What is the primary mechanism by which ACh is cleared from the synaptic cleft? -diffusion away from the synaptic cleft -reuptake into the synaptic terminal -broken down by acetylcholinesterase -endocytosis by synaptic vesicles
broken down by acetylcholinesterase
a type of voltage-gated ion channel located on the axon terminal.
calcium channel
What most directly causes synaptic vesicles to release acetylcholine into the synaptic cleft? -calcium entering the axon terminal -sodium entering the muscle fiber -depolarization of the sarcolemma -an action potential arriving at the axon terminal
calcium entering the axon terminal
The sliding of the myofilaments is directly initiated by the availability of which chemical at the myofibril? -potassium ions -sodium ions -calcium ions -acetylcholine
calcium ions
A muscle fiber represents which organizational level of anatomy? -tissue level -organ level -cellular level -organelle level
cellular level
In an isotonic contraction, the muscle ________. -changes in length and moves the "load" -rapidly resynthesizes creatine phosphate and ATP -does not change in length but increases tension -never converts pyruvate to lactate
changes in length and moves the "load"
Myofilaments represent which organizational level of anatomy? -chemical level -cellular level -organ level -tissue level
chemical level
Which of the following best describes the events of "contraction" in "excitation-contraction coupling"? -propagation of the action potential along the sarcolemma of the muscle fiber -cross bridge formation -release of calcium from the terminal cisternae -sliding of myofilaments
cross bridge formation
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
The sliding filament model of contraction states that __________. -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 calcium ions can be released from the sarcoplasmic reticulum -during contraction, the thin myofilaments slide past the thick myofilaments so that the actin and myosin myofilaments overlap to a greater degree -during contraction, the thin myofilaments slide past T tubules so that the Z discs are overlapping
during contraction, the thin myofilaments slide past the thick myofilaments so that the actin and myosin myofilaments overlap to a greater degree
A muscle that is lengthening while it produces tension is performing a(n) __________ contraction. -maximal -concentric -isometric -eccentric
eccentric
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? -elastic (titin) filaments -acetylcholine receptors in the motor end plate -thick (myosin) filaments -potassium (K+) leak channels
elastic (titin) filaments
Energy state of myosin for beginning cross bridge formation
energized/cocked myosin head
What is the functional role of the T tubules? -stabilize the G and F actin -synthesize ATP to provide energy for muscle contraction -hold cross bridges in place in a resting muscle -enhance cellular communication during muscle contraction
enhance cellular communication during muscle contraction
Which membrane surrounds the others? -exomysium -epimysium -endomysium -perimysium
epimysium
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 brain or spinal cord to the sarcolemma of a skeletal muscle fiber -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
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
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 -neurotransmitter release, motor neuron action potential, muscle cell action potential, release of calcium ions from SR, 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 -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
Which of the following would be recruited later in muscle stimulation when contractile strength increases? -motor units with larger, less excitable neurons -many small motor units with the ability to stimulate other motor units -motor units with the longest muscle fibers -large motor units with small, highly excitable neurons
motor units with larger, less excitable neurons
Which term best identifies a muscle cell? -myofibril -sarcomere -muscle fascicle -muscle fiber
muscle fiber
The two proteins directly involved in muscle contraction are broadly called ______.
myofilaments
A protein with heads that attach in cross bridging
myosin
When a muscle is unable to respond to stimuli temporarily, it is in which of the following periods? -relaxation period -fatigue period -latent period -refractory period
refractory period
What causes the power stroke? -release of ADP and Pi -binding of ATP -hydrolysis of ATP -calcium
release of ADP and Pi
ACh receptors are found mainly in the __________. -axon terminal -sarcolemma -synaptic vesicles -terminal cisternae
sarcolemma
The cell membrane of a muscle fiber is the ______.
sarcolemma
contractile unit of muscle
sarcomere
a type of voltage-gated ion channel located on the sarcolemma of the muscle fiber.
sodium channel
Creatine phosphate functions in the muscle cell by ________. -storing energy that will be transferred to ADP to resynthesize ATP -forming a temporary chemical compound with myosin -inducing a conformational change in the myofilaments -forming a chemical compound with actin
storing energy that will be transferred to ADP to resynthesize ATP
location of acetylcholinesterase
synaptic cleft
The force of a muscle contraction is NOT affected by __________. -the frequency of the stimulation -the number of muscle fibers stimulated -the degree of muscle stretch -the amount of ATP stored in the muscle cells -the size of the muscle fibers stimulated
the amount of ATP stored in the muscle cells
What does excess postexercise oxygen consumption represent? -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 -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 difference between the amount of oxygen needed for totally aerobic muscle activity and the amount actually used
Acetylcholine binds to its receptor in the sarcolemma and triggers __________. -the opening of voltage-gated calcium channels -the opening of ligand-gated anion channels -the opening of ligand-gated cation channels -the opening of calcium-release channels
the opening of ligand-gated cation channels
The mechanism of contraction in smooth muscle is different from skeletal muscle in that ________. -ATP energizes the sliding process -actin and myosin interact by the sliding filament mechanism -the trigger for contraction is a rise in intracellular calcium -the site of calcium binding site differs
the site of calcium binding site differs
A potential benefit of recruiting slow oxidative fibers for contraction before recruiting fast oxidative and fast glycolytic fibers might be ________. -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 -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 -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 facilitated transport of acetylcholine across the cleft -to pump Ca2+ back out of the axon terminal -to facilitate the entrance of acetylcholine into the muscle cell -to break down acetylcholine
to break down acetylcholine
blocks binding sites on actin
tropomyosin
blocks myosin binding sites on actin
tropomyosin
n muscle fibers, which regulatory protein blocks the attachment of myosin heads to actin? -thick filaments -acetylcholinesterase -tropomyosin -calcium
tropomyosin
When an action potential arrives at the axon terminal of a motor neuron, which ion channels open? -chemically gated calcium channels -voltage-gated potassium channels -voltage-gated calcium channels -voltage-gated sodium 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
