Podcast
Questions and Answers
What is the approximate molecular weight of a single acetylcholine receptor?
What is the approximate molecular weight of a single acetylcholine receptor?
- 1,000,000
- 275,000 (correct)
- 1,500,000
- 500,000
How many different types of subunit proteins are present in the fetal acetylcholine receptor complex?
How many different types of subunit proteins are present in the fetal acetylcholine receptor complex?
- 3
- 2
- 5 (correct)
- 4
What protein substitution occurs in the acetylcholine receptor complex during the transition from fetal to adult stages?
What protein substitution occurs in the acetylcholine receptor complex during the transition from fetal to adult stages?
- Epsilon protein replaces gamma protein (correct)
- Alpha protein replaces beta protein
- Gamma protein replaces epsilon protein
- Beta protein replaces gamma protein
What is the primary function of the acetylcholine receptor complex in the neuromuscular junction?
What is the primary function of the acetylcholine receptor complex in the neuromuscular junction?
How does the binding of acetylcholine to the receptor complex affect the channel structure?
How does the binding of acetylcholine to the receptor complex affect the channel structure?
What is the approximate diameter of the acetylcholine-gated channel?
What is the approximate diameter of the acetylcholine-gated channel?
Which of the following proteins are NOT part of the adult acetylcholine receptor complex?
Which of the following proteins are NOT part of the adult acetylcholine receptor complex?
What is the primary function of acetylcholine in the neuromuscular junction?
What is the primary function of acetylcholine in the neuromuscular junction?
What type of channels are located in the muscle fiber membrane near the mouths of the subneural clefts?
What type of channels are located in the muscle fiber membrane near the mouths of the subneural clefts?
Which of the following is NOT true about acetylcholine-gated ion channels?
Which of the following is NOT true about acetylcholine-gated ion channels?
What is the primary role of acetylcholine receptors in neuromuscular transmission?
What is the primary role of acetylcholine receptors in neuromuscular transmission?
What is the significance of the proximity of acetylcholine release sites to acetylcholine receptors?
What is the significance of the proximity of acetylcholine release sites to acetylcholine receptors?
Why do negative ions, like chloride ions, not pass through acetylcholine-gated ion channels?
Why do negative ions, like chloride ions, not pass through acetylcholine-gated ion channels?
What is the term for channels that open in response to a change in voltage across the membrane?
What is the term for channels that open in response to a change in voltage across the membrane?
Which of the following is NOT a positive ion that moves easily through acetylcholine-gated ion channels?
Which of the following is NOT a positive ion that moves easily through acetylcholine-gated ion channels?
What happens to acetylcholine in the synaptic cleft after it binds to its receptors?
What happens to acetylcholine in the synaptic cleft after it binds to its receptors?
What is the primary effect of curare on the neuromuscular junction?
What is the primary effect of curare on the neuromuscular junction?
What is the primary effect of botulinum toxin on the neuromuscular junction?
What is the primary effect of botulinum toxin on the neuromuscular junction?
What is the role of voltage-gated sodium channels in the initiation of an action potential at the neuromuscular junction?
What is the role of voltage-gated sodium channels in the initiation of an action potential at the neuromuscular junction?
What is the significance of the end plate potential being 'too weak to elicit an action potential' in the context of normal muscle function?
What is the significance of the end plate potential being 'too weak to elicit an action potential' in the context of normal muscle function?
Given the information presented, what process is most likely responsible for the rapid reformation of vesicles in the nerve terminal?
Given the information presented, what process is most likely responsible for the rapid reformation of vesicles in the nerve terminal?
Which of the following statements about the neuromuscular junction is TRUE?
Which of the following statements about the neuromuscular junction is TRUE?
What would happen if the nerve terminal were unable to reabsorb acetylcholine from the synaptic cleft?
What would happen if the nerve terminal were unable to reabsorb acetylcholine from the synaptic cleft?
What statement best describes the significance of the coated pits appearing in the nerve terminal membrane after an action potential?
What statement best describes the significance of the coated pits appearing in the nerve terminal membrane after an action potential?
What is the primary function of the Golgi apparatus in the process of acetylcholine formation and release?
What is the primary function of the Golgi apparatus in the process of acetylcholine formation and release?
What is the typical concentration of acetylcholine molecules within a single vesicle?
What is the typical concentration of acetylcholine molecules within a single vesicle?
What event triggers the release of acetylcholine from the vesicles?
What event triggers the release of acetylcholine from the vesicles?
Which of the following drugs disrupts the normal function of acetylcholinesterase?
Which of the following drugs disrupts the normal function of acetylcholinesterase?
How does the inactivation of acetylcholinesterase by drugs like neostigmine lead to muscle spasm?
How does the inactivation of acetylcholinesterase by drugs like neostigmine lead to muscle spasm?
What is the potential fatal consequence of prolonged muscle spasm due to acetylcholinesterase inhibition?
What is the potential fatal consequence of prolonged muscle spasm due to acetylcholinesterase inhibition?
How long can neostigmine and physostigmine inactivate acetylcholinesterase?
How long can neostigmine and physostigmine inactivate acetylcholinesterase?
What is the primary mechanism by which acetylcholinesterase inhibitors cause muscle spasm?
What is the primary mechanism by which acetylcholinesterase inhibitors cause muscle spasm?
What is the primary effect of diisopropyl fluorophosphate on nerve terminals?
What is the primary effect of diisopropyl fluorophosphate on nerve terminals?
What is the primary cause of myasthenia gravis?
What is the primary cause of myasthenia gravis?
What is the function of the T tubules in muscle cells?
What is the function of the T tubules in muscle cells?
How does the action potential at the neuromuscular junction trigger the release of acetylcholine?
How does the action potential at the neuromuscular junction trigger the release of acetylcholine?
Which of the following statements about curariform drugs is TRUE?
Which of the following statements about curariform drugs is TRUE?
What is the approximate number of acetylcholine vesicles that rupture with each action potential?
What is the approximate number of acetylcholine vesicles that rupture with each action potential?
How does the concentration of calcium ions within the nerve terminal affect the rate of acetylcholine vesicle fusion?
How does the concentration of calcium ions within the nerve terminal affect the rate of acetylcholine vesicle fusion?
What is the role of acetylcholinesterase in neuromuscular transmission?
What is the role of acetylcholinesterase in neuromuscular transmission?
What is the approximate resting membrane potential of skeletal muscle fibers compared to neurons?
What is the approximate resting membrane potential of skeletal muscle fibers compared to neurons?
How does the duration of an action potential in skeletal muscle compare to that in large myelinated nerves?
How does the duration of an action potential in skeletal muscle compare to that in large myelinated nerves?
What is the approximate velocity of conduction in skeletal muscle compared to large myelinated nerve fibers?
What is the approximate velocity of conduction in skeletal muscle compared to large myelinated nerve fibers?
What is the primary role of the transverse tubules (T tubules) in skeletal muscle fibers?
What is the primary role of the transverse tubules (T tubules) in skeletal muscle fibers?
Why is the sarcoplasmic reticulum (SR) important for muscle contraction?
Why is the sarcoplasmic reticulum (SR) important for muscle contraction?
What type of receptors are located on the T tubule membrane and are linked to calcium release channels in the SR?
What type of receptors are located on the T tubule membrane and are linked to calcium release channels in the SR?
What is the main function of the dihydropyridine receptors in skeletal muscle?
What is the main function of the dihydropyridine receptors in skeletal muscle?
Where are the ryanodine receptor channels located in the sarcoplasmic reticulum?
Where are the ryanodine receptor channels located in the sarcoplasmic reticulum?
Flashcards
End Plate Potential
End Plate Potential
Localized depolarization at the neuromuscular junction in muscle fibers.
Action Potential
Action Potential
Rapid change in membrane potential that propagates along the muscle fiber.
Voltage-Gated Sodium Channels
Voltage-Gated Sodium Channels
Membrane proteins that open to allow sodium ions influx during depolarization.
Curare
Curare
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Botulinum Toxin
Botulinum Toxin
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Neuromuscular Junction
Neuromuscular Junction
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Acetylcholine
Acetylcholine
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Self-Regenerative Effect
Self-Regenerative Effect
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Acetylcholine Receptors
Acetylcholine Receptors
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Ion Channels
Ion Channels
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Sodium Ions (Na+)
Sodium Ions (Na+)
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Depolarization
Depolarization
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Negative Ions Repulsion
Negative Ions Repulsion
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Transmitted Ion Quantity
Transmitted Ion Quantity
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Subneural Clefts
Subneural Clefts
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Acetylcholine Formation
Acetylcholine Formation
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Vesicle Size
Vesicle Size
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Acetylcholine Storage
Acetylcholine Storage
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Action Potential Arrival
Action Potential Arrival
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Muscle Spasm Cause
Muscle Spasm Cause
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Neostigmine
Neostigmine
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Acetylcholinesterase Function
Acetylcholinesterase Function
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Effects of Inhibition
Effects of Inhibition
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Diisopropyl fluorophosphate
Diisopropyl fluorophosphate
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Acetylcholine vesicles
Acetylcholine vesicles
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Curariform drugs
Curariform drugs
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Myasthenia Gravis
Myasthenia Gravis
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Acetylcholinesterase
Acetylcholinesterase
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Transverse Tubules
Transverse Tubules
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Sarcoplasmic Reticulum
Sarcoplasmic Reticulum
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Terminal Cisternae
Terminal Cisternae
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T Tubules
T Tubules
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Action Potential Duration
Action Potential Duration
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Calcium Ions Release
Calcium Ions Release
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Dihydropyridine Receptors
Dihydropyridine Receptors
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Ryanodine Receptor Channels
Ryanodine Receptor Channels
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Conduction Velocity
Conduction Velocity
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Fetal acetylcholine receptor
Fetal acetylcholine receptor
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Adult acetylcholine receptor
Adult acetylcholine receptor
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Calcium channels
Calcium channels
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Voltage-activated Na+ channels
Voltage-activated Na+ channels
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Acetylcholine-gated channel
Acetylcholine-gated channel
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Study Notes
Neuromuscular Junction and Impulse Transmission
- Skeletal muscle fibers are innervated by large myelinated nerve fibers from motoneurons in the spinal cord's anterior horns.
- Each nerve fiber branches to stimulate multiple skeletal muscle fibers.
- Each nerve ending forms a neuromuscular junction (motor end plate) near the muscle fiber midpoint (typically one per fiber).
- Action potentials from nerve signal travel in both directions.
Physiologic Anatomy of the Neuromuscular Junction
- Motor end plate: branching nerve terminals invaginating into muscle fiber, but outside the plasma membrane.
- Motor end plate covered by Schwann cells, providing insulation.
- Synaptic gutter/trough: invaginated membrane
- Synaptic space/cleft: space between nerve terminal and muscle fiber membrane (20-30 nm wide).
- Subneural clefts: smaller folds in muscle membrane increasing surface area.
- Mitochondria in axon terminal provide ATP, the energy source used for acetylcholine synthesis.
- Acetylcholine (Ach) produced in cytosol and absorbed into small synaptic vesicles (up to 300,000 per end plate).
- Acetylcholinesterase (enzyme) in synaptic space destroys acetylcholine rapidly (milliseconds).
Secretion of Acetylcholine
- Nerve impulse triggers release of ~125 acetylcholine vesicles into synaptic space (see Figure 7-2).
- Action potential triggers opening of voltage-gated calcium channels in nerve terminal.
- Calcium influx activates Ca2+-calmodulin-dependent protein kinase, which phosphorylates docking proteins attached to vesicles.
- Acetylcholine vesicles released from cytoskeletal anchor proteins to active zone via exocytosis.
- Acetylcholine released at active zone beside dense bars in neural membrane.
Acetylcholine Opens Ion Channels
- Acetylcholine receptors numerous on muscle fiber membrane (located primarily near subneural clefts).
- Receptors are protein complexes (total molecular weight ~275,000).
- Fetal receptors contain alpha, beta, delta, and gamma subunits; adult receptors replace gamma with epsilon.
- Acetylcholine binding to the alpha subunits opens the ion channel, causing conformational change.
- Channel opening allows sodium (Na+), potassium (K+), and calcium (Ca2+) ions to pass through.
- Sodium movement primarily inward due to electrochemical gradient. Large sodium influx through channels results in end-plate potential causing greater sodium influx, initiating an action potential.
Destruction of Acetylcholine and End Plate Potential
- Acetylcholinesterase rapidly degrades released acetylcholine (few milliseconds), preventing sustained muscle excitation.
- End plate potential: localized positive potential change inside muscle fiber membrane due to sodium influx.
- End plate potential strong enough to initiate an action potential and muscle fiber depolarization.
Excitation-Contraction Coupling
- Action potential spreads along muscle membrane, triggering action potentials in T tubules that penetrate the muscle fiber interior.
- Voltage changes in T tubules cause calcium release from sarcoplasmic reticulum.
- Calcium influx initiates muscle contraction.
- Calcium pump removes calcium from the myofibrillar fluid (sarcoplasm) and initiates muscle relaxation.
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Description
This quiz explores the structure and function of the neuromuscular junction, focusing on the interaction between nerve fibers and skeletal muscle fibers. It covers topics such as the role of motor end plates, synaptic transmission, and the physiological anatomy involved in impulse transmission between nerves and muscles.
