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