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The sarcolemma is a thick membrane that surrounds myofibrils.
The sarcolemma is a thick membrane that surrounds myofibrils.
False
Titin molecules play a role in the elastic properties of myosin and actin filaments during muscle contraction.
Titin molecules play a role in the elastic properties of myosin and actin filaments during muscle contraction.
True
Calcium ions released from the sarcoplasmic reticulum are responsible for initiating the repulsive forces between actin and myosin filaments.
Calcium ions released from the sarcoplasmic reticulum are responsible for initiating the repulsive forces between actin and myosin filaments.
False
The neurotransmitter acetylcholine is released at the endings of motor nerves to stimulate muscle contraction.
The neurotransmitter acetylcholine is released at the endings of motor nerves to stimulate muscle contraction.
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The action potential in muscle fibers causes the sarcoplasmic reticulum to absorb large quantities of calcium ions.
The action potential in muscle fibers causes the sarcoplasmic reticulum to absorb large quantities of calcium ions.
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Magnesium enhances the function of voltage-dependent channels by competing with Ca2+.
Magnesium enhances the function of voltage-dependent channels by competing with Ca2+.
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Acetylcholine esterase is found in the postsynaptic motor end plate of the neuromuscular junction.
Acetylcholine esterase is found in the postsynaptic motor end plate of the neuromuscular junction.
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In a synapse, one action potential in a presynaptic neuron can lead to an action potential in the postsynaptic neuron without any summation.
In a synapse, one action potential in a presynaptic neuron can lead to an action potential in the postsynaptic neuron without any summation.
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The binding of neurotransmitters at the neuromuscular junction is always excitatory, resulting in an end plate potential.
The binding of neurotransmitters at the neuromuscular junction is always excitatory, resulting in an end plate potential.
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Smooth muscle cells possess a motor end-plate region for neurotransmitter reception.
Smooth muscle cells possess a motor end-plate region for neurotransmitter reception.
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The resultant change in membrane potential at the neuromuscular junction is considered a graded potential.
The resultant change in membrane potential at the neuromuscular junction is considered a graded potential.
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Smooth muscle contraction is regulated through direct innervation by motor neurons via a motor end-plate.
Smooth muscle contraction is regulated through direct innervation by motor neurons via a motor end-plate.
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Inhibition of skeletal muscles can be achieved at the neuromuscular junction level.
Inhibition of skeletal muscles can be achieved at the neuromuscular junction level.
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The receptor potential is typically a depolarization of the afferent neuron's receptor initiated by changes in channel permeability resulting from physical injury.
The receptor potential is typically a depolarization of the afferent neuron's receptor initiated by changes in channel permeability resulting from physical injury.
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Summation of EPSPs involves either temporal or spatial summation in efferent neurons and interneurons.
Summation of EPSPs involves either temporal or spatial summation in efferent neurons and interneurons.
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The end-plate potential occurs in smooth muscle due to binding of neurotransmitter to receptors on the surface membrane.
The end-plate potential occurs in smooth muscle due to binding of neurotransmitter to receptors on the surface membrane.
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Pacemaker potential refers to a gradual depolarization of the membrane in smooth muscle and cardiac muscle due to automatic channel permeability changes.
Pacemaker potential refers to a gradual depolarization of the membrane in smooth muscle and cardiac muscle due to automatic channel permeability changes.
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Slow-wave potential is characterized by rapid, sustained depolarization swings in potential that always reach threshold in gastrointestinal smooth muscle.
Slow-wave potential is characterized by rapid, sustained depolarization swings in potential that always reach threshold in gastrointestinal smooth muscle.
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Myasthenia gravis primarily enhances the function of acetylcholine receptor-channels.
Myasthenia gravis primarily enhances the function of acetylcholine receptor-channels.
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The process of depolarization in skeletal muscle is not influenced by the binding of acetylcholine (ACh).
The process of depolarization in skeletal muscle is not influenced by the binding of acetylcholine (ACh).
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Efferent neurons can only experience spatial summation of EPSPs, not temporal summation.
Efferent neurons can only experience spatial summation of EPSPs, not temporal summation.
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Calcium entering at the NMJ is responsible for the release of neurotransmitters like acetylcholine.
Calcium entering at the NMJ is responsible for the release of neurotransmitters like acetylcholine.
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The gradual changes in channel permeability in pacemaker potential are primarily responsible for the oscillatory nature of the depolarization.
The gradual changes in channel permeability in pacemaker potential are primarily responsible for the oscillatory nature of the depolarization.
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Cardiac muscle fibers are made up of individual cells connected only in parallel with one another.
Cardiac muscle fibers are made up of individual cells connected only in parallel with one another.
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The atrial syncytium constitutes the walls of the two ventricles.
The atrial syncytium constitutes the walls of the two ventricles.
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At the NMJ, the driving force of sodium is weaker than that of potassium.
At the NMJ, the driving force of sodium is weaker than that of potassium.
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Smooth muscle in the gastrointestinal tract only exhibits slow-wave potential without any influence from external factors.
Smooth muscle in the gastrointestinal tract only exhibits slow-wave potential without any influence from external factors.
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The electrical activity of the heart is reflected in the ECG, which also provides information about mechanical activity.
The electrical activity of the heart is reflected in the ECG, which also provides information about mechanical activity.
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An action potential in muscle fibers can occur below the threshold level.
An action potential in muscle fibers can occur below the threshold level.
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The specialized conductive system responsible for conducting potentials from the atrial syncytium to the ventricular syncytium is called the A-V bundle.
The specialized conductive system responsible for conducting potentials from the atrial syncytium to the ventricular syncytium is called the A-V bundle.
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The acetylcholine-gated channels allow potassium ions to enter the muscle fibers.
The acetylcholine-gated channels allow potassium ions to enter the muscle fibers.
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The end plate potential can increase the electrical potential in the muscle fiber by as much as 50 to 75 millivolts.
The end plate potential can increase the electrical potential in the muscle fiber by as much as 50 to 75 millivolts.
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Pacemaker cells in the heart are incapable of generating rhythmic potentials independently.
Pacemaker cells in the heart are incapable of generating rhythmic potentials independently.
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The SA node is responsible for initiating the excitation sequence in the heart.
The SA node is responsible for initiating the excitation sequence in the heart.
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End plate potentials A and C are strong enough to initiate an action potential.
End plate potentials A and C are strong enough to initiate an action potential.
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Acetylcholinesterase functions to cleave acetylcholine into acetate and choline.
Acetylcholinesterase functions to cleave acetylcholine into acetate and choline.
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The electrocardiogram shows simultaneous action potentials at different levels of the heart conduction system.
The electrocardiogram shows simultaneous action potentials at different levels of the heart conduction system.
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Nicotinic receptors are found exclusively in the brain.
Nicotinic receptors are found exclusively in the brain.
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The atrioventricular (A-V) node is located between the atria and the ventricles.
The atrioventricular (A-V) node is located between the atria and the ventricles.
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Repolarization of the muscle fiber occurs without the need for potassium current.
Repolarization of the muscle fiber occurs without the need for potassium current.
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Gap junctions in cardiac muscle fibers prevent the diffusion of ions.
Gap junctions in cardiac muscle fibers prevent the diffusion of ions.
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The Purkinje fibers are part of the heart's mechanical activity rather than electrical activity.
The Purkinje fibers are part of the heart's mechanical activity rather than electrical activity.
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The summation of graded potentials is necessary for action potential initiation in muscle fibers.
The summation of graded potentials is necessary for action potential initiation in muscle fibers.
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Study Notes
Skeletal Muscle Contraction
- The sarcolemma is a thin membrane surrounding a skeletal muscle fiber
- Myofibrils are composed of actin and myosin filaments
- Titin filaments hold myosin and actin in place, extending from the Z disk to the M line
- The sarcoplasm is the fluid between myofibrils
- The sarcoplasmic reticulum is the specialized endoplasmic reticulum of skeletal muscle
Steps for Muscle Contraction
- An action potential travels along a motor nerve to its endings on the muscle fiber
- At each ending, acetylcholine is released
- Acetylcholine acts on the muscle fiber membrane, opening acetylcholine-gated channels
- Na+ ions diffuse into the muscle fiber, causing depolarization
- This triggers voltage-gated sodium channels, initiating an action potential
- The action potential travels along the muscle fiber membrane
- The action potential depolarizes the muscle membrane, and the electricity flows through the center of the muscle fiber
- The sarcoplasmic reticulum releases calcium ions, causing actin and myosin to interact and slide, leading to contraction
- After this, calcium is pumped back into the sarcoplasmic reticulum, ending the contraction
Neuromuscular Junction (NMJ)
- The NMJ is the synapse between a motor neuron and a skeletal muscle fiber
- The motor unit is a motor neuron and the innervated muscle cells
- A neuromuscular junction is formed from the large myelinated nerve fiber and the branching nerve terminals that invaginate into the muscle fiber surface
- The synaptic gutter, the synaptic space or cleft in the invaginated membrane is 20 to 30 nanometers wide.
Events at the NMJ
- Calcium enters the axon terminal and neurotransmitters are released (acetylcholine)
- Acetylcholine binds to receptors, opening sodium and potassium channels
- Depolarization is called an end-plate potential, a graded potential
- Action potential in the muscle occurs once the threshold is reached. There is no summation needed
- Neurotransmitters are cleared by acetylcholinesterase, breaking down acetylcholine into acetate and choline.
- The muscle repolarizes, going back to the reversal potential.
End Plate Potential (EPP)
- A sudden influx of sodium ions into the muscle fiber causes depolarization at the end plate.
- The EPP creates a local potential called the end-plate potential.
- It is graded (changes in amplitude), and it spreads out from the end plate.
Action Potential in Skeletal Muscle
- Similar to nerve action potentials, but with quantitative differences
- The resting membrane potential is about -80 to -90 mV
- The duration of the action potential is 1 to 5 milliseconds
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Description
This quiz covers the essential aspects of skeletal muscle contraction, including the structure of muscle fibers and the biochemical steps leading to muscle contraction. Understand the roles of the sarcolemma, myofibrils, and neurotransmitters in the process. Gain insights into how electrical signals trigger muscle actions.
