Exam 3: Anatomy and Physiology Practice test
The Contraction Cycle (Six Steps)
1: Calcium ions arrive within the zone of the overlap. 2: Calcium ions bind to troponin. Active sites on actin are exposed. 3: The myosin heads bind to actin active sites. 4: The myosin head pivots (power stoke). ADP and P are released. 5: ATP binds to the myosin head. 6: The free myosin head "recocks" ADP and P are released. -The contraction cycle begins with the arrival of calcium ions to the zones of overlap via excitation-contraction coupling. -Then, calcium ions bind to the troponin-tropomyosin complex, causing troponin to change position. Troponin's movement rolls tropomyosin away from actin's active sites, thus allowing them to form cross-bridges with energized myosin heads. After cross-bridge formation, the energy that was stored in the resting state is released as the myosin head pivots towards the M line (coincident with the release of bound ADP and P). This is known as the power stroke. Finally, to disengage cross-bridges following the power stroke, ATP binds to the myosin head, and the bond between myosin and actin is broken. Myosin is reactivated for further cycling when ATP is converted into ADP and P, and the myosin head returns to its original conformation
During anaerobic glycolysis -ATP is produced. -carbohydrate is metabolized. -oxygen is not consumed. -pyruvic acid is produced. -All of the answers are correct.
All of the answers are correct.
When a skeletal muscle fiber contracts, - the zones of overlap get larger. - the width of the A band remains constant. - the H bands and I bands get smaller. - the Z lines get closer together. - All of the answers are correct.
All of the answers are correct.
When comparing slow muscle fibers to fast muscle fibers, slow fibers -take about three times as long to reach peak tension. -are rich in the red protein myoglobin. -generate much less tension. -have much smaller fiber diameters. -All of the answers are correct.
All of the answers are correct.
Which of these would lead to increased oxygen consumption? -increased muscle activity -increased aerobic respiration by muscle cells -increased conversion of lactic acid to glucose -increased heat production -All of the answers are correct.
All of the answers are correct.
Which of these is true of cardiac muscle fibers? -Cardiac fibers branch. -Cardiac fibers have a single nucleus. -Cardiac fibers have a long twitch duration compared to skeletal fibers. -All of these are true of cardiac fibers.
All of these are true of cardiac fibers.
To increase muscle tension, the nervous system can... -increase the number of active motor units -recruit larger motor units -increase the stimulation frequency -All of these can increase muscle tension.
All of these can increase muscle tension.
How would the loss of acetylcholinesterase from the motor end plate affect skeletal muscle? -It would have little effect on skeletal muscles. -It would make the muscles less excitable. -It would produce muscle weakness. -It would cause flaccid paralysis (muscles are relaxed and unable to contract). -It would cause spastic paralysis (muscles are contracted and unable to relax).
It would cause spastic paralysis (muscles are contracted and unable to relax).
In a sarcomere, thick filaments are linked laterally by proteins of the - H band. - I band. - M line. - A band. - Z line.
M line.
Which of the following is not characteristic of smooth muscle? -The thin filaments of smooth muscle fibers are attached to dense bodies. -Smooth muscle connective tissue forms tendons and aponeuroses. -Neurons that innervate smooth muscles are under involuntary control. -Smooth muscle cells are uninucleate. -Smooth muscles do not contain sarcomeres.
Smooth muscle connective tissue forms tendons and aponeuroses.
The muscle action potentials that initiate contraction are transmitted from the sarcolemma into the interior of the muscle fiber by -T tubules -myofibrils -myofilaments -the sarcoplasmic reticulum
T tubules -T tubules conduct muscle action potentials into the interior of the muscle fiber. The extensive T tubule network within a muscle fiber ensures that all myofibrils within that cell contract simultaneously.
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 increased action potential generation in the sarcolemma. -The muscles would relax because of calcium being pumped back into the sarcoplasmic reticulum. -The muscles would contract because of increased nerve stimulation. -The muscles would contract because of calcium binding to troponin.
The muscles would contract because of calcium binding to troponin. -The excess calcium leaked from the sarcoplasmic reticulum would initiate the contraction cycle by binding to troponin on the thin filaments. In the case of MH, this contraction does not end, because the sarcoplasmic reticulum is constantly leaking calcium, even in the absence of muscle excitation by neurons. This constant muscle contraction consumes large amounts of ATP. Large amounts of heat are produced as metabolism increases to meet these ATP demands. Without treatment, MH is typically fatal because of a dramatic increase in body temperature.
What happens immediately after the myosin head binds to the active site on actin? -The myosin head detaches from the active site on actin. -ATP binds to the myosin head. -The myosin head pivots, moving the actin strand. -Tropomyosin moves away from the active site on actin.
The myosin head pivots, moving the actin strand. -When the myosin head binds to actin, the head pivots towards the center of the sarcomere. This action moves the actin strand, pulling the Z-lines inward. This is the basis of sarcomere shortening during muscle contraction.
A single motor neuron together with all the muscle fibers it innervates is called -a dermatome. -an end foot. -a myotome. -an end plate. -a motor unit.
a motor unit.
Sarcomere is best defined as... - a repeating unit of striated muscle - actomyosin proteins -a storage form of calcium -thick and thin filaments
a repeating unit of striated muscle
The rapid rise and fall in force produced by a muscle fiber after a single action potential is -an end plate potential. -a twitch. -an unfused tetanus. -a muscle action potential. -a tetanus.
a twitch.
During neuromuscular transmission, the axon terminals release -acetylcholine -sodium ions -acetylcholinesterase -calcium ions
acetylcholine
Triggering of the muscle action potential occurs after -the nerve action potential jumps across the neuromuscular junction. -acetylcholine binds to chemically-gated channels in the end plate membrane. -acetylcholinesterase binds to receptors on the end plate. -calcium ion binds to channels on the end plate. -Any of the above can produce an action potential in the muscle cell.
acetylcholine binds to chemically-gated channels in the end plate membrane.
The cytoplasm of the neuromuscular terminal contains vesicles filled with molecules of the neurotransmitter -norepinephrine. -acetylcholine. -adrenaline. -epinephrine. -antidiuretic hormone.
acetylcholine.
Which of the following proteins contains the active site involved in cross-bridge formation? -myosin -actin -tropomyosin -troponin
actin -The active site on actin is where myosin heads bind. In the absence of calcium, these active sites are covered by the regulatory protein tropomyosin.
Myosin molecules form cross-bridges when they attach to __________. -troponin -tropomyosin -calcium -actin
actin -The attachment of a myosin head is a linkage between the thick and thin filaments--a cross-bridge. These molecules remain attached through the force-generating power stroke of the cross-bridge cycle.
The biochemical reaction that consumes the majority of a muscle's ATP is the... -neuromuscular transmission -muscle action potential -sodium-potassium pump -actin myosin cross-bridge cycle
actin myosin cross-bridge cycle
The most important factor in decreasing the intracellular concentration of calcium ion after contraction is -diffusion of calcium out of the cell. -active transport of calcium into the sarcoplasmic reticulum. -diffusion of calcium into the sarcoplasmic reticulum. -active transport of calcium into the synaptic cleft. -active transport of calcium across the sarcolemma.
active transport of calcium into the sarcoplasmic reticulum.
Creatine phosphate -can replace ATP in binding to myosin molecules during contraction. -is produced by the process of anaerobic respiration. -acts as an energy reserve in muscle tissue. -is only formed during strenuous exercise. -cannot transfer its phosphate group to ADP.
acts as an energy reserve in muscle tissue.
During the recovery period the body's need for oxygen is increased because -the muscles are not producing ATP. -additional oxygen is required to restore energy reserves consumed during exercise. -muscle cells are producing energy anaerobically. -the individual is panting. -the liver requires more oxygen to produce lactic acid.
additional oxygen is required to restore energy reserves consumed during exercise.
A resting muscle generates most of its ATP by -aerobic metabolism of fatty acids. -glycogenolysis. -the tricarboxylic acid cycle. -hydrolysis of creatine phosphate. -anaerobic respiration.
aerobic metabolism of fatty acids.
What causes the vesicles inside a neuron to fuse with the plasma membrane? -an action potential in the neuron -acetylcholine binding to acetylcholine receptors -acetylcholine being broken down by acetylcholinesterase -an action potential in the muscle fiber
an action potential in the neuron -When an action potential arrives at the synaptic terminal, acetylcholine-filled vesicles fuse with the plasma membrane. This releases acetylcholine into the synaptic cleft. The released acetylcholine eventually generates an action potential in the muscle fiber.
After heavy exercise, if energy reserves in a muscle are depleted, ________ occurs. -treppe -paralysis -atrophy -tetanus -an oxygen debt
an oxygen debt
Muscles are attached to bones by tendons or... - ligaments - aponeuroses - perimysium - superficial fascia
aponeuroses
The sarcoplasmic reticulum contains... -myofilaments -troponin -T tubules -calcium
calcium -Calcium is released from the sarcoplasmic reticulum when an action potential arrives in an adjacent T tubule.
Active sites on the actin become available for binding after -calcium binds to tropomyosin. -actin binds to troponin. -troponin binds to tropomyosin. -calcium binds to troponin. -myosin binds to troponin.
calcium binds to troponin.
ATP binding leads to which of the following actions? -pivoting of the myosin head -cross-bridge formation -detaching and resetting cross-bridges -exposure of active sites on actin
detaching and resetting cross-bridges -ATP binding causes the myosin head to detach from actin. The energy from ATP hydrolysis is then used to reactivate the myosin head. This energy use is similar to setting a mouse trap, where the energy is used to set the trap, not to release the trap.
The dense layer of connective tissue that surrounds an entire skeletal muscle is the - fascicle. - tendon. -endomysium. -epimysium. -perimysium.
epimysium
Synaptic vesicles contain neurotransmitters that are released by ________ when the action potential arrives. -endocytosis -exocytosis -hydrolysis -apoptosis -sodium
exocytosis
Inside a muscle, bundles of single muscle fibers form... -fascicles - tubules -thick filaments -sarcomeres
fascicles -Single muscle fibers are bundled into groups, called fascicles. A whole muscle is a large bundle of fascicles.
The __________ type of muscle fiber has relatively few mitochondria -intermediate -cardiac -fast -slow
fast
Which of the following is not a function of smooth muscle tissue? -moving food materials along the digestive tract -forcing blood from the heart into the major arteries -forcing urine out of the urinary tract -elevating hairs on the arm -altering the diameter of the respiratory passageways
forcing blood from the heart into the major arteries
During the Cori cycle, in the liver -glucose is produced from lactic acid. -glucose is released from glycogen. -lactic acid is produced from glucose. -lactic acid is shuffled to muscle cells. -lactic acid is produced from pyruvic acid.
glucose is produced from lactic acid.
Fast fibers -have many mitochondria. -have low resistance to fatigue. -have low resistance to fatigue and have quick twitches. -have twitches with a very brief contraction phase. -rely on aerobic metabolism.
have low resistance to fatigue and have quick twitches.
Muscle fibers differ from "typical cells" in that muscle fibers - lack a plasma membrane. - lack mitochondria. - have large gaps in the cell membrane. - have many nuclei. - are very small.
have many nuclei.
All of the following are found in both skeletal and cardiac muscle fibers except... -intercalated disks -striations -mitochondria -sarcomeres
intercalated disks
When a muscle contraction develops tension but doesn't shorten the muscle, the contraction is called... -isometric -unfused tetanus -isotonic -incomplete twitch
isometric
Muscle fatigue occurs due to a buildup of __________ and __________ in pH. -creatine phosphate; decrease -creatine phosphate; increase -lactic acid; increase -lactic acid; decrease
lactic acid; decrease
The muscle weakness of myasthenia gravis results from -inability of the muscle fiber to produce ATP. -excessive acetylcholinesterase that destroys the neurotransmitter. -the motor neuron action potential being too small to shock the muscle fibers. -insufficient acetylcholine release from presynaptic vesicles. -loss of acetylcholine receptors in the end-plate membrane.
loss of acetylcholine receptors in the end-plate membrane.
Myofibrils are... -made of a series of sarcomeres -proteins that cover active sites on actin -bundles of muscle cells inside a whole muscle -connections between actin and myosin
made of a series of sarcomeres -Myofibrils are formed when sarcomeres are connected end to end, creating a long strand of contractile segments, each shortening during a contraction. A contraction causes the entire myofibril to shorten like an accordion.
When acetylcholine binds to receptors at the motor end plate, the end plate membrane becomes -less permeable to sodium ions. -less permeable to potassium ions. -repolarized. -more permeable to sodium ions. -more permeable to calcium ions.
more permeable to sodium ions.
Receptors for acetylcholine are located on the -transverse tubule. -synaptic cleft. -synaptic knob. -sarcomere. -motor end plate.
motor end plate.
The neuromuscular junction is a connection between a neuron and a... -synaptic terminal -myofibril -vesicle -muscle fiber
muscle fiber -The neuromuscular junction is a connection between two cells -- a neuron and a muscle fiber. Overall, the neuromuscular junction allows action potentials in the neuron to generate action potentials in the muscle fiber. This is accomplished through the release of the chemical acetylcholine from the synaptic terminal of the neuron.
In an isotonic contraction, -tension rises and falls but the muscle length is constant. -muscle tension exceeds the load and the muscle lifts the load. -many twitches always fuse into one. -the peak tension is less than the load. -postural muscles stabilize the vertebrae.
muscle tension exceeds the load and the muscle lifts the load.
Skeletal muscle fibers are formed from embryonic cells called - fascicles. - myomeres. - myofibrils. - myoblasts. - sarcomeres.
myoblasts.
Which thick filament binds to actin once its active binding sites are exposed? - tropomyosin - actin - myosin - troponin
myosin -Myosin is a thick filament that contains a hinge, allowing its interaction with actin when binding sites are exposed.
Which of the following is involved in the power stroke? -Z lines -myofibrils -tropomyosin -myosin
myosin -The myosin head pivots at the head after it binds to actin, causing the thin filament to be pulled towards the center of the sarcomere. This motion causes the muscle to shorten during contraction.
Each skeletal muscle fiber is controlled by a motor neuron at a single -neuromuscular junction. -synaptic cleft. -synaptic knob. -transverse tubule. -sarcomere.
neuromuscular junction.
Acetylcholine receptors are primarily located... -on the motor end plate -inside the muscle fiber -on the synaptic terminal -inside vesicles
on the motor end plate -Receptors for acetylcholine are located on the motor end plate -- the portion of the muscle fiber's sarcolemma that faces the neuron's synaptic terminal. Binding of acetylcholine to acetylcholine receptors increases the sodium permeability of the motor end plate. This causes sodium to rush into the muscle fiber, which generates a muscle action potential.
Anaerobic glycolysis provides energy for muscle contraction when the supply of __________ is limited. -glucose -pyruvic acid -oxygen -ATP
oxygen
A thin layer of connective tissue that surrounds a muscle fascicle is called the.. -tendon -epimysium -perimysium -endomysium
perimysium
The ability of smooth muscle to function over a wide range of lengths is called -contractility. -plasticity. -variability. -elasticity. -extensibility.
plasticity.
Skeletal muscle does each of these except.. -maintain posture -ventilate the lungs -pump blood -produce movement
pump blood
A patient takes a medication that blocks ACh receptors of skeletal muscle fibers. What is this drug's effect on skeletal muscle contraction? -reduces the muscle's ability for contraction -increases the muscle's excitability -increases tone in the muscle -causes a strong contraction similar to a "charlie horse" cramp -produces a strong, continuous state of contraction
reduces the muscle's ability for contraction
The role of acetylcholinesterase in the neuromuscular junction is to... -generate a muscle action potential -release acetylcholine from the synaptic terminal -increase the sodium permeability of the motor end plate -remove acetylcholine from the synaptic cleft
remove acetylcholine from the synaptic cleft -Acetylcholinesterase is an enzyme that's always present in the synaptic cleft. It breaks down acetylcholine soon after acetylcholine is released from the synaptic terminal. This breakdown is the primary mechanism for clearing acetylcholine from the synaptic cleft.
Fast muscle fibers can adapt to aerobic metabolism by generating more mitochondria in response to -increased levels of testosterone. -sustained low levels of muscle activity. -repeated, exhaustive stimulation. -prolonged periods of inactivity. -high amounts of oxygen
repeated, exhaustive stimulation.
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 -oxygen debt. -tetany. -treppe. -rigor mortis. -depolarization
rigor mortis.
The plasma membrane of a skeletal muscle fiber is called the -sarcosome. - sarcomere. - sarcoplasmic reticulum. - sarcoplasm. - sarcolemma.
sarcolemma.
Z lines define the edges of which of the following? -myofibrils -sarcomeres -cross-bridges -myosin
sarcomeres -Z-lines define the outer border of each sarcomere. When sarcomeres are connected end to end, the Z lines represent the link from one sarcomere to the other.
In response to an action potential along the transverse tubules, the __________ release(s) calcium ions into the sarcoplasm. -calcitonin -thin filaments -troponin molecules -sarcoplasmic reticulum
sarcoplasmic reticulum
The series of membranous channels that surround each myofibril is the - sarcoplasmic reticulum. - sarcoplasm. - endomysium. - sarcolemma. - sarcomere.
sarcoplasmic reticulum
Which organelle completely surrounds each myofibril inside a muscle fiber? -sarcoplasmic reticulum -calcium -nucleus -fascicle
sarcoplasmic reticulum -Myofibrils are surrounded by the sarcoplasmic reticulum. This ensures that the calcium concentration in the myofibril rises rapidly during excitation-contraction coupling. Within a millisecond, the calcium concentration in and around a myofibril can increase 100 fold.
Since each myofibril is attached at either end of the muscle fiber, when sarcomeres shorten, the muscle fiber -shortens. -strengthens. - lengthens. - pulls from the middle. - weakens.
shortens
Which type of muscle tissue has the greatest effect on the body's heat production? -smooth -cardiac -skeletal -All of these muscle types have about the same effect on the body's heat production
skeletal
The type of muscle fiber that is most resistant to fatigue is the ________ fiber. -intermediate -slow -anaerobic -high-density -fast
slow
The narrow space between the synaptic terminal and the muscle fiber is the -synaptic knob. -synaptic cleft. -motor end plate. -M line. -motor unit
synaptic cleft.
The end of a neuron, where acetylcholine-filled vesicles are located, is called the... -motor end plate -acetylcholine receptor -synaptic cleft -synaptic terminal
synaptic terminal -Acetylcholine-filled vesicles are found in the synaptic terminals of motor neurons. The synaptic terminal is at the end of the neuron's axon, so you can think of the axon "terminating" at the synaptic terminal.
The advantage of having many nuclei in a skeletal muscle fiber is - the ability to produce nutrients for muscle contraction. - the ability to contract. - the ability to produce large amounts of the muscle proteins needed for growth and repair. - the ability to produce more ATP with little oxygen. - the ability to store extra DNA for metabolism.
the ability to produce large amounts of the muscle proteins needed for growth and repair
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 binding of calcium to troponin -the formation of cross-bridges
the generation of an action potential in the sarcolemma -The electrical impulse, or action potential, in the sarcolemma is the result of nerve stimulation at the neuromuscular junction. Both nerve cells (neurons) and the muscle fibers are excitableâ€"they can both generate and conduct action potentials.
An action potential in the muscle fiber causes... -acetylcholinesterase to break down acetylcholine -acetylcholine to bind to receptors on the motor end plate -the release of acetylcholine into the synaptic cleft -the muscle fiber to contract
the muscle fiber to contract -Once the muscle fiber is excited by an action potential, it contracts through the process of excitation-contraction coupling. Cells that generate action potentials, such as muscle fibers and neurons, are known as "excitable" cells.
Which arrangement of the sarcomere gives rise to the structure (band or line) indicated by the arrow? -the boundary between adjacent sarcomeres -the region of the resting sarcomere that only contains thick filaments -is the point of connection for adjacent thick filaments -the region of the sarcomere that contains only thin filaments
the region of the sarcomere that contains only thin filaments -The I band extends from the A band of one sarcomere to the A band of the neighboring sarcomere and is the region where only thin filaments are found.
What is the synaptic cleft? -the space between the synaptic terminal and the motor end plate -the region of the neuron containing synaptic vesicles -the border between the motor end plate and the sarcolemma -the step where acetylcholinesterase (AChE) breaks down, or cleaves, acetylcholine
the space between the synaptic terminal and the motor end plate -The synaptic cleft is the gap between the neuron and muscle fiber into which acetylcholine is released. The acetylcholine is released from vesicles in the neuron's synaptic terminal. Acetylcholine then binds to receptors embedded in the muscle fiber's motor end plate (a specialized region of the sarcolemma).
Myosin molecules form what part of the sarcomere? -actin -thin filament -thick filament -tropomyosin
thick filament -Many myosin molecules make up a single thick filament. The head of each myosin molecule can potentially form a cross-bridge to a nearby thin filament.
Which of the following phrases best describes how excitation is coupled to contraction in skeletal muscle fibers? -through cross-bridge formation -through calcium release from the sarcoplasmic reticulum -through electrical impulses travelling along the sarcolemma -through T tubules
through calcium release from the sarcoplasmic reticulum -The excitation of muscle fibers leads to calcium release, which, in turn, facilitates the contraction cycle. The contractile proteins within myofibrils are not directly sensitive to action potentials. This means that an intermediate step must couple the electrical impulse in the T tubules to contraction in the myofibrils. This intermediate step is the release of calcium from the sarcoplasmic reticulum.
The muscle action potential penetrates into a fiber along the -sarcoplasmic reticulum -neuromuscular junction -Z discs -transverse tubules
transverse tubules
The action potential is conducted into a skeletal muscle fiber by -triads. -neuromuscular junctions. -motor end plates. -sarcoplasmic reticulum. -transverse tubules.
transverse tubules.
T tubules and the terminal cisternae are clustered into structures called... -fascicles -myofibrils -triads -sarcomeres
triads -Triads are made of a single T tubule located between two terminal cisternae of the sarcoplasmic reticulum. Triads are the site where action potentials arriving in the T tubule lead to calcium release from the sarcoplasmic reticulum.
When the sarcomere is at rest, what is covering the active sites on actin? -cross-bridges -troponin -tropomyosin -myosin
tropomyosin -Tropomyosin is the rope-like regulatory protein that covers the active sites on actin, preventing cross-bridges from forming.
At rest, active sites on the actin are blocked by - troponin molecules. - myosin molecules. - calcium ions. - tropomyosin molecules. - ATP molecules.
tropomyosin molecules.
When calcium ion binds to troponin, -myosin shortens. -tropomyosin moves into the groove between the helical actin strands. -actin heads will bind to myosin. -active sites on the myosin are exposed. -muscle relaxation occurs.
tropomyosin moves into the groove between the helical actin strands.
Which of the following causes the active site on actin to be exposed or uncovered? -cross-bridge formation -calcium entering the sarcoplasmic reticulum -troponin releasing calcium -tropomyosin shifting position
tropomyosin shifting position -Tropomyosin is the regulatory protein that covers the active sites on actin. When tropomyosin shifts over, the active sites become available to myosin for cross-bridge formation.
To what regulatory protein does calcium bind during the initiation of the contraction cycle in skeletal muscle fibers? -myosin -troponin -actin -tropomyosin
troponin -Once released from the sarcoplasmic reticulum, calcium binds to troponin, which then causes a shift in the position of tropomyosin, exposing the active sites on actin. Once these active sites are exposed, cross-bridges form, and the contraction cycle proceeds.
When calcium is released inside a muscle cell, what does it bind to? -myosin -tropomyosin -troponin -actin
troponin -Troponin has a binding site for calcium, which initiates the exposure of the active sites on actin.
At rest, the tropomyosin molecule is held in place by - actin molecules. - troponin molecules. - ATP molecules. - myosin molecules. - calcium ions.
troponin molecules.
Inside a neuron, acetylcholine is contained within... -vesicles -the synaptic cleft -the motor end plate -acetylcholine receptors
vesicles -Acetylcholine is contained within vesicles, which are small membranous sacs. When an action potential arrives at the synaptic terminal, these vesicles fuse with the neuronal plasma membrane, releasing acetylcholine into the synaptic cleft. A single vesicle contains thousands of acetylcholine molecules.
In a sarcomere, cross-bridge attachment occurs specifically in the -zone of overlap. -A band. -I band. -H band. -M line.
zone of overlap.
