Mastering A & P Chapter
Aerobic metabolism normally provides ________ percent of the ATP demands of a resting muscle cell. 25 100 95 50 70
95
The cross bridge cycle is a series of molecular events that occur after excitation of the sarcolemma. What is a cross bridge? Troponin bound to tropomyosin Calcium bound to troponin ATP bound to a myosin head A myosin head bound to actin
A myosin head bound to actin
A triad is composed of a T-tubule and two adjacent terminal cisternae of the sarcoplasmic reticulum. How are these components connected? Voltage-gated sodium channels. Myosin cross-bridge binding sites. Potassium leak channels. A series of proteins that control calcium release.
A series of proteins that control calcium release.
After a power stroke, the myosin head must detach from actin before another power stroke can occur. What causes cross bridge detachment? ADP and inorganic phosphate are bound to the myosin head. Acetylcholine binds to receptors in the junctional folds of the sarcolemma. ATP binds to the myosin head. Calcium ions bind to troponin.
ATP binds to the myosin head.
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 diffuses away from the cleft. Acetylcholine is transported into the postsynaptic neuron by receptor-mediated endocytosis. Acetylcholine is transported back into the axon terminal by a reuptake mechanism.
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 and moves across the synaptic cleft bound to a transport 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 binds to its receptor in the junctional folds of the sarcolemma. Its receptor is linked to a G protein. Acetylcholine is released by axon terminals of the motor neuron.
Acetylcholine is released by axon terminals of the motor neuron.
During anaerobic glycolysis oxygen is not consumed. pyruvic acid is produced. carbohydrate is metabolized. ATP is produced. All of the answers are correct.
All of the answers are correct.
In rigor mortis the myosin heads are attached to actin. cross-bridge cycling is absent. muscles are inextensible. ATP is depleted. All of the answers are correct.
All of the answers are correct.
When a skeletal muscle fiber contracts, the Z lines get closer together. the H bands and I bands get smaller. the zones of overlap get larger. the width of the A band remains constant. All of the answers are correct.
All of the answers are correct.
When comparing slow muscle fibers to fast muscle fibers, slow fibers have much smaller fiber diameters. are rich in the red protein myoglobin. take about three times as long to reach peak tension. generate much less tension. All of the answers are correct.
All of the answers are correct.
Which of the following is a recognized function of skeletal muscle? maintain posture guard body entrances and exits maintain body temperature produce movement All of the answers are correct.
All of the answers are correct.
Which statement about the microscopic anatomy of skeletal muscle fibers is true? Each fiber has many nuclei. Muscle fibers are continuous from tendon to tendon. Cross striations result from the lateral alignment of thick and thin filaments. Tubular extensions of the sarcolemma penetrate the fiber transversely. All of the answers are correct.
All of the answers are correct.
hich of the following statements is (are) true regarding human muscles? Slow fibers are abundant in the back muscles. Most have both slow and fast fibers. Eye muscles are composed entirely of fast fibers. Slow fibers are abundant in the calf muscles. 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 long twitch duration compared to skeletal fibers. Cardiac fibers have a single nucleus. All of these are true of cardiac fibers.
All of these are true of cardiac fibers.
To increase muscle tension, the nervous system can __________. recruit larger motor units increase the stimulation frequency increase the number of active motor units All of these can increase muscle tension.
All of these can increase muscle tension.
The 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 endplate. Binding of the neurotransmitter causes chemically gated sodium channels to open in the motor end plate. Binding causes voltage-gated sodium channels to open in the motor endplate. Binding causes chemically gated potassium channels to open in the motor end plate.
Binding of the neurotransmitter causes chemically gated sodium channels to open in the motor end plate.
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 nuclei. Calcium ions are stored in the mitochondria. Calcium ions are stored in the transverse tubules. Calcium ions are stored in the sarcoplasmic reticulum.
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 troponin and change its shape. Sodium ions bind to troponin and change its shape. Calcium ions bind to tropomyosin and change its shape. Calcium release channels open in the sarcoplasmic reticulum, and calcium levels rise in the sarcoplasm.
Calcium ions bind to troponin and change its shape.
Which of the following is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers? Sodium ions. Action potentials. Acetylcholine. Calcium ions.
Calcium ions.
Excitation of the sarcolemma is coupled or linked to the contraction of a skeletal muscle fiber. What specific event initiates the contraction? Action potentials propagate into the interior of the skeletal muscle fiber. Calcium release from the sarcoplasmic reticulum initiates the contraction. Voltage-sensitive proteins change shape. Sodium release from the sarcoplasmic reticulum initiates the contraction.
Calcium release from the sarcoplasmic reticulum initiates the contraction.
Which of the following statements is false? Cardiac muscle stimulation is neural. Cardiac muscle contractions cannot be summated. Skeletal muscle stimulation is neural. Skeletal muscle contractions may be summated. Cardiocytes are interconnected through intercalated di
Cardiac muscle stimulation is neural.
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 ATP binds to the myosin head. Cross bridge cycling ends when calcium release channels in the sarcoplasmic reticulum open.
Cross bridge cycling ends when sufficient calcium has been actively transported back into the sarcoplasmic reticulum to allow calcium to unbind from troponin.
Excitation-contraction coupling is a series of events that occur after the events of the neuromuscular junction have transpired. The term excitation refers to which step in the process? Excitation refers to the propagation of action potentials along the axon of a motor neuron. Excitation refers to the shape change that occurs in voltage-sensitive proteins in the sarcolemma. Excitation refers to the release of calcium ions from the sarcoplasmic reticulum. Excitation, in this case, refers to the propagation of action potentials along the sarcolemma.
Excitation, in this case, refers to the propagation of action potentials along the sarcolemma.
The region of the sarcomere that always contains thin filaments is the H band. A band. I band. Z line. M line.
I band.
The "rest and recovery" period, where the muscle restores depleted reserves, includes all of the following processes EXCEPT __________. Pyruvic acid is converted back to lactic acid. Glycogen is synthesized from glucose molecules. Oxygen rebinds to myoglobin. ATP is used to rephosphorylate creatine into creatine phosphate.
Pyruvic acid is converted back to lactic acid.
Cycling of myosin cross-bridges results in ___________. force production muscle shortening ATP hydrolysis Repeated cycling of cross-bridges causes all of these effects.
Repeated cycling of cross-bridges causes all of these effects.
Calcium entry into the axon terminal triggers which of the following events? 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. Acetylcholine binds to its receptor. Cation channels open and sodium ions enter the axon terminal while potassium ions exit the axon terminal.
Synaptic vesicles fuse to the plasma membrane of the axon terminal and release acetylcholine.
The muscle action potentials that initiate contraction are transmitted from the sarcolemma into the interior of the muscle fiber by __________. the sarcoplasmic reticulum T tubules myofibrils myofilaments
T tubules
How does the myosin head obtain the energy required for activation? The energy comes from oxidative phophorylation. The energy comes from the hydrolysis of GTP. The energy comes from the direct phosphorylation of ADP by creatine phosphate. 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 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. Potassium ions diffuse inward 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.
The inside surface of the sarcolemma is negatively charged compared to the outside surface. Sodium ions diffuse inward along favorable chemical and electrical gradients.
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 relax because of calcium being pumped back into the sarcoplasmic reticulum. The muscles would contract because of calcium binding to troponin. The muscles would contract because of increased nerve stimulation. 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? 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 detaches 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 cross bridge The triad The sarcomere The junctional folds of the sarcolemma
The sarcomere
Which of these is not a property of slow muscle fibers? They resist fatigue. They are rich in myoglobin. They contract slowly. They are large in diameter.
They are large in diameter.
What is the relationship between the number of motor neurons recruited and the number of skeletal muscle fibers innervated? A motor neuron typically innervates only one skeletal muscle fiber. Motor neurons always innervate thousands of skeletal muscle fibers. Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron. A skeletal muscle fiber is innervated by multiple motor neurons.
Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron.
A single muscle action potential will normally be followed by __________. a single pulse of calcium ion release treppe two pulses of calcium ion release incomplete tetanus
a single pulse of calcium ion release
The skeletal muscle complex known as the triad consists of actin, myosin, and filaments. actin, myosin, and sarcomeres. filaments, myofibrils, and sarcomeres. A bands, H bands, and I bands. a transverse tubule and two terminal cisternae.
a transverse tubule and two terminal cisternae.
During neuromuscular transmission, the axon terminals release __________. acetylcholinesterase sodium ions calcium ions acetylcholine
acetylcholine
In a neuromuscular junction, synaptic vesicles in the motor neuron contain which neurotransmitter? dopamine serotonin norepinephrine acetylcholine (ACh)
acetylcholine (ACh)
The cytoplasm of the neuromuscular terminal contains vesicles filled with molecules of the neurotransmitter norepinephrine. antidiuretic hormone. epinephrine. acetylcholine. adrenaline.
acetylcholine.
How is acetylcholine (ACh) removed from the synaptic cleft? diffusion away from the synaptic cleft acetylcholinesterase (AChE; an enzyme) a reuptake pump on the axon terminal
acetylcholinesterase (AChE; an enzyme)
A myosin head binds to which molecule to form a cross bridge? 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 __________. tropomyosin troponin actin calcium
actin
Which of the following proteins contains the active site involved in cross-bridge formation? troponin actin myosin tropomyosin
actin
Creatine phosphate acts as an energy reserve in muscle tissue. is only formed during strenuous exercise. is produced by the process of anaerobic respiration. cannot transfer its phosphate group to ADP. can replace ATP in binding to myosin molecules during contraction.
acts as an energy reserve in muscle tissue.
During the recovery period the body's need for oxygen is increased because the individual is panting. the liver requires more oxygen to produce lactic acid. additional oxygen is required to restore energy reserves consumed during exercise. muscle cells are producing energy anaerobically. the muscles are not producing ATP.
additional oxygen is required to restore energy reserves consumed during exercise.
A resting muscle generates most of its ATP by the tricarboxylic acid cycle. anaerobic respiration. aerobic metabolism of fatty acids. hydrolysis of creatine phosphate. glycogenolysis.
aerobic metabolism of fatty acids.
What causes the vesicles inside a neuron to fuse with the plasma membrane? an action potential in the muscle fiber an action potential in the neuron acetylcholine being broken down by acetylcholinesterase acetylcholine binding to acetylcholine receptors
an action potential in the neuron
Muscles are attached to bones by tendons or __________. ligaments aponeuroses perimysium superficial fascia
aponeuroses
What causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum within a muscle cell? ATP troponin arrival of an action potential calcium ion pump
arrival of an action potential
What causes the myosin head to disconnect from actin? binding of calcium binding of ATP binding of troponin hydrolysis of ATP
binding of ATP
The sarcoplasmic reticulum contains __________. calcium myofilaments troponin T tubules
calcium
A muscle producing its maximum tension is in __________. incomplete tetanus complete tetanus rigor mortis treppe
complete tetanus
Muscle tissue, one of the four basic tissue groups, consists chiefly of cells that are highly specialized for peristalsis. cushioning. conduction. contraction. secretion.
contraction.
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
Titin is a(n) __________. tropomyosin-binding protein thin filament protein elastic protein calcium-binding protein
elastic protein
The capillaries that wrap around each muscle fiber are located within the __________. perimysium sarcolemma endomysium epimysium
endomysium
The dense layer of connective tissue that surrounds an entire skeletal muscle is the tendon. epimysium. endomysium. perimysium. fascicle.
epimysium.
Synaptic vesicles contain neurotransmitters that are released by ________ when the action potential arrives. hydrolysis apoptosis exocytosis sodium endocytosis
exocytosis
What means of membrane transport is used to release the neurotransmitter into the synaptic cleft? exocytosis a protein carrier a channel
exocytosis
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 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 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
Inside a muscle, bundles of single muscle fibers form __________. T tubules sarcomeres thick filaments fascicles
fascicles
The __________ type of muscle fiber has relatively few mitochondria. slow cardiac fast intermediate
fast
Large-diameter, densely packed myofibrils, large glycogen reserves, and few mitochondria are characteristics of fatty muscles. slow fibers. intermediate fibers. fast fibers. red muscles.
fast fibers.
During the Cori cycle, in the liver lactic acid is shuffled to muscle cells. lactic acid is produced from glucose. glucose is produced from lactic acid. lactic acid is produced from pyruvic acid. glucose is released from glycogen.
glucose is produced from lactic acid.
Muscle fibers differ from "typical cells" in that muscle fibers lack a plasma membrane. have large gaps in the cell membrane. are very small. have many nuclei. lack mitochondria.
have many nuclei.
What energizes the power stroke? binding of ATP calcium hydrolysis of ATP
hydrolysis of ATP
All of the following are found in both skeletal and cardiac muscle fibers except __________. sarcomeres intercalated disks striations mitochondria
intercalated disks
Which arrangement of the sarcomere gives rise to the M line? is the point of connection for adjacent thick filaments the region of the resting sarcomere that only contains thick filaments the boundary between adjacent sarcomeres the region of the sarcomere that contains only thin filaments
is the point of connection for adjacent thick filaments
The type of contraction in which the muscle fibers do not shorten is called isotonic. isometric. concentric. treppe. tetany.
isometric.
Muscle fatigue occurs due to a buildup of __________ and __________ in pH. lactic acid; decrease creatine phosphate; increase creatine phosphate; decrease lactic acid; increase
lactic acid; decrease
The muscle weakness of myasthenia gravis results from insufficient acetylcholine release from presynaptic vesicles. excessive acetylcholinesterase that destroys the neurotransmitter. inability of the muscle fiber to produce ATP. the motor neuron action potential being too small to shock the muscle fibers. 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 bundles of muscle cells inside a whole muscle connections between actin and myosin proteins that cover active sites on actin
made of a series of sarcomeres
During activities requiring aerobic endurance oxygen debts are common. oxygen is not required. glycogen and glycolysis are the primary sources of reserve energy. fatigue occurs in a few minutes. most of the muscle's energy is produced in mitochondri
most of the muscle's energy is produced in mitochondri
Interactions between actin and myosin filaments of the sarcomere are responsible for the striped appearance of skeletal muscle. muscle contraction. the conduction of neural stimulation to the muscle fiber. muscle relaxation. muscle fatigue.
muscle contraction.
The neuromuscular junction is a connection between a neuron and a __________. synaptic terminal muscle fiber myofibril vesicle
muscle fiber
In an isotonic contraction, postural muscles stabilize the vertebrae. tension rises and falls but the muscle length is constant. muscle tension exceeds the load and the muscle lifts the load. the peak tension is less than the load. many twitches always fuse into one.
muscle tension exceeds the load and the muscle lifts the load.
In which of the following would the motor units have the fewest muscle fibers? thigh muscles calf muscles postural muscles of the back muscles that control the eyes muscles of the neck
muscles that control the eyes
Skeletal muscle fibers are formed from embryonic cells called myomeres. fascicles. sarcomeres. myoblasts. myofibrils.
myoblasts.
Which of the following is involved in the power stroke? myosin Z lines myofibrils tropomyosin
myosin
Which thick filament binds to actin once its active binding sites are exposed? troponin tropomyosin actin myosin
myosin
Each skeletal muscle fiber is controlled by a motor neuron at a single sarcomere. transverse tubule. neuromuscular junction. synaptic knob. synaptic cleft.
neuromuscular junction.
Acetylcholine receptors are primarily located __________. inside the muscle fiber inside vesicles on the motor end plate on the synaptic terminal
on the motor end plate
What is the function of the T Tubules? making of ATP - the "power house" of the cell houses the genetic material of the cell part of coupling the action potential to contraction storage of calcium
part of coupling the action potential to contraction
A thin layer of connective tissue that surrounds a muscle fascicle is called the __________. epimysium endomysium tendon perimysium
perimysium
Resting smooth muscle can be stretched without developing much tension because of its __________. extensibility contractility plasticity elasticity
plasticity
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 produces a strong, continuous state of contraction causes a strong contraction similar to a "charlie horse" cramp increases tone in the muscle increases the muscle's excitability
reduces the muscle's ability for contraction
The role of acetylcholinesterase in the neuromuscular junction is to __________. remove acetylcholine from the synaptic cleft increase the sodium permeability of the motor end plate release acetylcholine from the synaptic terminal generate a muscle action potential
remove acetylcholine from the synaptic cleft
Which of the following best describes the term sarcomere? repeating unit of striated myofibrils protein that accounts for elasticity of resting muscle thin filaments are anchored here largely made of myosin molecules storage site for calcium ions
repeating unit of striated myofibrils
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 rigor mortis. treppe. tetany. depolarization. oxygen debt.
rigor mortis.
The action potential in skeletal muscle fibers is generated by the __________. sarcoplasm sarcophagus sarcoplasmic reticulum sarcolemma
sarcolemma
The plasma membrane of a skeletal muscle fiber is called the sarcoplasmic reticulum. sarcoplasm. sarcolemma. sarcosome. sarcomere.
sarcolemma.
The repeating unit of a skeletal muscle fiber is the sarcolemma. sarcoplasmic reticulum. myofibril. myofilament. sarcomere.
sarcomere.
Z lines define the edges of which of the following? myofibrils cross-bridges sarcomeres myosin
sarcomeres
In response to an action potential along the transverse tubules, the __________ release(s) calcium ions into the sarcoplasm. troponin molecules sarcoplasmic reticulum thin filaments calcitonin
sarcoplasmic reticulum
Which organelle completely surrounds each myofibril inside a muscle fiber? calcium fascicle sarcoplasmic reticulum nucleus
sarcoplasmic reticulum
Which type of muscle tissue has the greatest effect on the body's heat production? skeletal smooth cardiac 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 anaerobic fast high-density slow
slow
Which of the following best describes the term sarcoplasmic reticulum? repeating unit of striated myofibrils largely made of myosin molecules storage and release site for calcium ions protein that accounts for elasticity of resting muscle thin filaments are anchored here
storage and release site for calcium ions
What is the function of the Sarcoplasmic Reticulum? storage of calcium houses the genetic material of the cell part of coupling the action potential to contraction making of ATP - the "power house" of the cell
storage of calcium
The narrow space between the synaptic terminal and the muscle fiber is the motor unit. M line. synaptic knob. synaptic cleft. motor end plate.
synaptic cleft.
The end of a neuron, where acetylcholine-filled vesicles are located, is called the __________. motor end plate synaptic terminal acetylcholine receptor synaptic cleft
synaptic terminal
At each end of the muscle, the collagen fibers of the epimysium, and each perimysium and endomysium, come together to form a ligament. satellite cell. tenosynovium. tendon. sheath.
tendon.
The bundle of collagen fibers at the end of a skeletal muscle that attaches the muscle to bone is called a(n) ligament. epimysium. fascicle. myofibril. tendon.
tendon.
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 sarcolemma terminal cisternae of the sarcoplasmic reticulum cytosol
terminal cisternae of the sarcoplasmic reticulum
Which arrangement of the sarcomere gives rise to the Z line? 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 boundary between adjacent sarcomeres
the boundary between adjacent sarcomeres
Which of the following most correctly describes excitation in the context of excitation-contraction coupling in skeletal muscle? the binding of calcium to troponin the release of calcium by the sarcoplasmic reticulum the generation of an action potential in the sarcolemma the formation of cross-bridges
the generation of an action potential in the sarcolemma
Which of the following acts as an ATPase during the contraction cycle of muscle? the head portion of the myosin molecule tropomyosin molecules the tail portion of the myosin molecule actin molecules troponin molecules
the head portion of the myosin molecule
An action potential in the muscle fiber causes __________. acetylcholinesterase to break down acetylcholine the release of acetylcholine into the synaptic cleft acetylcholine to bind to receptors on the motor end plate the muscle fiber to contract
the muscle fiber to contract
Acetylcholine binds to its receptor in the sarcolemma and triggers __________. the opening of calcium-release channels the opening of voltage-gated calcium channels the opening of ligand-gated anion channels the opening of ligand-gated cation channels
the opening of ligand-gated cation channels
Which arrangement of the sarcomere gives rise to the H band? the region of the sarcomere that contains only thin filaments 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 resting sarcomere that only contains thick filaments
Which arrangement of the sarcomere gives rise to the I band? the region of the resting sarcomere that only contains thick filaments the boundary between adjacent sarcomeres the region of the sarcomere that contains only thin filaments is the point of connection for adjacent thick filaments
the region of the sarcomere that contains only thin filaments
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
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 T tubules through electrical impulses travelling along the sarcolemma through calcium release from the sarcoplasmic reticulum through cross-bridge formation
through calcium release from the sarcoplasmic reticulum
What is name given to the regularly spaced infoldings of the sarcolemma? sarcoplasmic reticulum transverse or T tubules terminal cisternae motor endplates
transverse or T tubules
The muscle action potential penetrates into a fiber along the __________. sarcoplasmic reticulum neuromuscular junction transverse tubules Z discs
transverse tubules
T tubules and the terminal cisternae are clustered into structures called __________. fascicles myofibrils sarcomeres triads
triads
When the sarcomere is at rest, what is covering the active sites on actin? myosin cross-bridges tropomyosin troponin
tropomyosin
When calcium ion binds to troponin, actin heads will bind to myosin. myosin shortens. active sites on the myosin are exposed. muscle relaxation occurs. tropomyosin moves into the groove between the helical actin strands.
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
The binding of calcium to which molecule causes the myosin binding sites to be exposed? actin troponin tropomyosin
troponin
To what regulatory protein does calcium bind during the initiation of the contraction cycle in skeletal muscle fibers? actin tropomyosin myosin troponin
troponin
When calcium is released inside a muscle cell, what does it bind to? tropomyosin myosin actin troponin
troponin
Which component of a thin filament binds to calcium once the calcium ion is released from the sarcoplasmic reticulum? troponin actin tropomyosin myosin
troponin
Inside a neuron, acetylcholine is contained within __________. the synaptic cleft acetylcholine receptors the motor end plate vesicles
vesicles
When an action potential arrives at the axon terminal of a motor neuron, which ion channels open? voltage-gated sodium channels chemically gated calcium channels voltage-gated potassium channels voltage-gated calcium channels
voltage-gated calcium channels
