Multiple Choice Questions

Myosin head energy status during the power stroke:
  • returns to energized position
  • pivots and returns to low energy
  • acting-binding sites exposed
  • ratchets toward the M line
What is the status of actin and myosin during the cocking of the myosin head phase?
  • returns to energized position
  • transverse or T tubules
  • they are both detached
  • membrane of muscle cell
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?
  • pivots and returns to low energy
  • they are both detached
  • Acetylcholine receptor
  • cross bridge detachment
what is sarcoplasm?
  • the cytoplasm of a skeletal muscle fiber
  • transverse or T tubules
  • Contractile unit
  • Made up of several sarcomeres
Arrange the sequence of events at the NMJ from first to last.
  • Step 1. Action potential arives at the axon terminalStep 2. Calcium ions enter the axon terminalStep 3. Synaptic vesicles fuse to membrane of axon terminal.Step 4. Acetylcholine is released into the synaptic cleft.Step 5. Acetylcholine binds to its receptors on the junctional folds.Step 6. Junctional folds become depolarized.Step 7. Action potential is initiated on the sarcolemma.
  • 1. the activated myosin head binds to actin, forming a cross bridge2. ADP is released and myosin slides the thin filament toward the center of the sarcomere3. ATP binds to the myosin head and detaches it from actin4. ATP is hydrolyzed to ADP and P, and the energy released re-cocks the myosin head.
  • ADP and Pi
  • A series of events in which an electrical stimulus is conveyed to a muscle fiber to enact contraction.
The prefix ________ means flesh.
  • myo-
  • iso-
  • tropo-
  • sarco-
is not bound to myosin during the detachment step.
  • acting-binding sites exposed
  • Troponin
  • ADP
  • ADP and Pi
What is the status of ATP during the cocking of the myosin head phase?
  • ratchets toward the M line
  • transverse or T tubules
  • returns to energized position
  • hydrolyzed to ADP and Pi
What is actin?
  • myofilament with a knob-like head
  • Blocks myosin-binding sites on actin
  • the cytoplasm of a skeletal muscle fiber
  • myofilament stiffened and stabilized by tropomyosin
Which selection best describes the initial event in contraction?
  • Calcium binds to troponin, which moves tropomyosin and exposes the myosin-binding sites on actin.
  • Myosin heads bind to the newly exposed myosin-binding sites on actin to form cross bridges.
  • myofilaments
  • A series of events in which an electrical stimulus is conveyed to a muscle fiber to enact contraction.
The cell membrane of a muscle fiber is the?
  • sarcolemma
  • myofilaments
  • Troponin
  • ADP and Pi
_____________enzyme located in the synaptic cleft that breaks down acetylcholine.
  • Acetylcholine receptor
  • Acetylcholine
  • Acetylcholinesterase
  • Tropomyosin
The prefix means abnormal, diseased.
  • sarco-
  • myo-
  • dys-
  • tropo-
1.___________________________ : the swollen chamber of an organelle that lies on either side of a T tubule
  • Voltage sensitive tubule protien
  • cistern
  • Troponin
  • T tubule
Excitation of the sarcolemma is coupled or linked to the contraction of a skeletal muscle fiber. What specific event initiates the contraction?
  • Release of acetylcholine from the synaptic vesicles
  • Calcium ions.
  • Calcium release from the sarcoplasmic reticulum initiates the contraction.
  • A series of events in which an electrical stimulus is conveyed to a muscle fiber to enact contraction.
___________the space between the axon terminal and junctional folds.
  • Synaptic cleft
  • Calcium channel
  • Acetylcholine
  • Tropomyosin
1.Location of higher concentration of Ca2+ needed for cross bridge formation and cycling:
  • cytoplasm
  • Troponin
  • isometric
  • myofilaments
A triad is composed of a T-tubule and two adjacent terminal cisternae of the sarcoplasmic reticulum. How are these components connected?
  • Release of acetylcholine from the synaptic vesicles
  • Calcium release from the sarcoplasmic reticulum initiates the contraction.
  • A series of proteins that control calcium release.
  • A series of events in which an electrical stimulus is conveyed to a muscle fiber to enact contraction.
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?
  • Excitation, in this case, refers to the propagation of action potentials along the sarcolemma.
  • The subunits of the troponin in cardiac muscle are unique to heart muscle.
  • Cross bridge detachment cannot occur. Detachment requires ATP, which is produced only during life
  • Calcium release from the sarcoplasmic reticulum initiates the contraction.
What is name given to the regularly spaced infoldings of the sarcolemma?
  • ratchets toward the M line
  • transverse or T tubules
  • hydrolyzed to ADP and Pi
  • returns to energized position
What is a sarcomere?
  • bundle of skeletal muscle fibers enclosed by connective tissue called perimysium
  • myofilament with a knob-like head
  • the cytoplasm of a skeletal muscle fiber
  • Contractile unit
Energy state of myosin for beginning cross bridge formation:
  • hydrolyzed to ADP and Pi
  • energized/cocked myosin head
  • they are both detached
  • acting-binding sites exposed
The two proteins directly involved in muscle contraction are broadly called?
  • myofilaments
  • myofilament with a knob-like head
  • Myosin
  • Synaptic cleft
Inadequate calcium in the neuromuscular junction would directly affect which of the following processes?
  • Voltage sensitive tubule protien
  • A series of proteins that control calcium release.
  • Release of acetylcholine from the synaptic vesicles
  • returns to energized position
2.____________________ : a protein that changes shape as a direct result of an action potential
  • Acetylcholinesterase
  • Voltage sensitive tubule protien
  • cistern
  • Tropomyosin
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?
  • Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron.
  • It allows calcium to exit the sarcoplasmic reticulum and enter the cytosol
  • 1. the activated myosin head binds to actin, forming a cross bridge2. ADP is released and myosin slides the thin filament toward the center of the sarcomere3. ATP binds to the myosin head and detaches it from actin4. ATP is hydrolyzed to ADP and P, and the energy released re-cocks the myosin head.
  • 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.
Neuromuscular Junction at rest consists of?
  • A series of events in which an electrical stimulus is conveyed to a muscle fiber to enact contraction.
  • 1. the activated myosin head binds to actin, forming a cross bridge2. ADP is released and myosin slides the thin filament toward the center of the sarcomere3. ATP binds to the myosin head and detaches it from actin4. ATP is hydrolyzed to ADP and P, and the energy released re-cocks the myosin head.
  • No Na+ diffusionChemically-gated channels closedCalcium channels closedACh in synaptic vesiclesMore negative charges inside sarcolemma
  • Ca2+ from the sarcoplasmic reticulum binds to troponin
Neuromuscular Junction active consists of?
  • ADP and Pi
  • Ca2+ from the sarcoplasmic reticulum binds to troponin
  • ACh in synaptic cleftCalcium channels openChemically-gated channels openNa+ diffusionLess negative charges inside sarcolemma
  • ratchets toward the M line
Botulism and myasthenia gravis are conditions that cause muscle weakness. Which of these statements is NOT true?
  • 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.
  • Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron.
  • A series of proteins that control calcium release.
  • Both conditions are caused by an inability of the body to produce adequate acetylcholine.
The molecules released just before power stroke:
  • sarcolemma
  • pivots and returns to low energy
  • Dystrophin
  • ADP and Pi
Only __________ of the myosin heads are detached from actin at any one time while calcium is present and cycling continues.
  • Acetylcholine
  • Calcium channel
  • Tropomyosin
  • one-half
Myasthenia gravis is a disease resulting from an autoimmune attack on the ACh receptors of the motor end plate. Binding of antibodies to the ACh receptors results in generalized muscle weakness that progresses as more ACh receptors are destroyed. Which of the following medications would help alleviate the muscle weakness?
  • a drug that binds to and inactivates acetylcholinesterase (neostigmine)
  • It allows calcium to exit the sarcoplasmic reticulum and enter the cytosol
  • Ca2+ from the sarcoplasmic reticulum binds to troponin
  • Calcium release from the sarcoplasmic reticulum initiates the contraction.
_________ is a missing protein in Duschenne 19s muscular dystrophy
  • Dystrophin
  • Synaptic cleft
  • Acetylcholinesterase
  • Acetylcholine
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?
  • cross bridge detachment
  • Excitation, in this case, refers to the propagation of action potentials along the sarcolemma.
  • The subunits of the troponin in cardiac muscle are unique to heart muscle.
  • returns to energized position
___________________a type of voltage-gated ion channel located on the sarcolemma of the muscle fiber.
  • Tropomyosin
  • Troponin
  • Sodium channel
  • cistern
1.The bond between the actin and myosin head weakens as a result of this during the X-bridge detachment phase
  • cistern
  • ATP
  • tropo-
  • ADP
___________membranous sac located in the axon terminal that contains neurotransmitter.
  • Acetylcholine
  • Tropomyosin
  • Calcium channel
  • Synaptic vesicle
________________ has an affinity for myosin binding sites in the absence of calcium.
  • Troponin
  • Synaptic vesicle
  • Tropomyosin
  • Dystrophin
During an exercise where muscles do not shorten, ______________ contractions have occurred.
  • cistern
  • Motor neuron
  • Tropomyosin
  • isometric
The prefix ______________ means muscle.
  • dys-
  • myo-
  • sarco-
  • tropo-
______________a type of chemically-gated ion channel located on the junctional folds of the muscle fiber.
  • Acetylcholine receptor
  • Acetylcholinesterase
  • Synaptic vesicle
  • Voltage sensitive tubule protien
If troponin is a component of both cardiac and skeletal muscle, why is an elevated plasma troponin level useful in diagnosing myocardial damage?
  • The subunits of the troponin in cardiac muscle are unique to heart muscle.
  • Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron.
  • A series of proteins that control calcium release.
  • Excitation, in this case, refers to the propagation of action potentials along the sarcolemma.
what are smyofibrils?
  • transverse or T tubules
  • the cytoplasm of a skeletal muscle fiber
  • Long, cylindrical cells
  • Made up of several sarcomeres
Which selection correctly describes the role of calcium in coupling?
  • 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.
  • A series of events in which an electrical stimulus is conveyed to a muscle fiber to enact contraction.
  • Calcium binds to troponin, which moves tropomyosin and exposes the myosin-binding sites on actin.
  • Myosin heads bind to the newly exposed myosin-binding sites on actin to form cross bridges.
4.________________ : a structure that forms a path from the membrane to the cell interior
  • Troponin
  • T tubule
  • Acetylcholinesterase
  • Voltage sensitive tubule protien
what are skeletal muscle fibers?
  • Made up of several sarcomeres
  • membrane of muscle cell
  • Long, cylindrical cells
  • transverse or T tubules
Actin behavior during the power stroke:
  • ratchets toward the M line
  • hydrolyzed to ADP and Pi
  • Long, cylindrical cells
  • they are both detached
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Multiple Choice Questions
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