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Questions and Answers
What type of receptors are located at the motor end plate?
What initiates the conformational change in the nicotinic receptors?
Which ions are involved when acetylcholine binds to nicotinic receptors?
What type of channels are the nicotinic receptors classified as?
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What is the primary neurotransmitter that interacts with nicotinic receptors at the neuromuscular junction?
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What triggers the opening of ligand-gated Na+ channels?
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What happens to the permeability of the motor end plate when ligand-gated Na+ channels open?
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Which ion's permeability primarily increases due to the conformational change in the ligand-gated Na+ channel?
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What is the role of acetylcholine in the context of ligand-gated Na+ channels?
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What occurs following the binding of acetylcholine to its receptor sites?
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What is the neuromuscular junction?
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What triggers the release of acetylcholine at the neuromuscular junction?
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Which component is released from synaptic vesicles at the neuromuscular junction?
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What is a motor unit?
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What effect does Ca2+ have in the presynaptic terminal at the neuromuscular junction?
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Study Notes
The Neuromuscular Junction
- The connection between a somatic motor neuron and a muscle fiber is called the neuromuscular junction, an example of a chemical synapse
- Somatic motor neurons are the nerves that innervate muscle fibers
- A motor unit is a single motor neuron and all the muscle fibers it innervates
Sequence of Events at the Neuromuscular Junction
- Action Potential Arrival: Action potentials arriving at the presynaptic terminal trigger voltage-gated calcium channels to open
- Calcium Influx: Calcium ions (Ca2+) diffuse into the presynaptic terminal causing synaptic vesicles containing the neurotransmitter acetylcholine to release their contents into the synaptic cleft
- Acetylcholine Release: Acetylcholine, the neurotransmitter, diffuses across the synaptic cleft
- Acetylcholine Binding: Acetylcholine binds to nicotinic receptors on the motor end plate. These receptors are ligand-gated ion channels.
- Sodium Ion Channels Open: Binding of acetylcholine to nicotinic receptors causes a conformational change, opening the central core of the channel and increasing the permeability of the motor end plate to sodium (Na+) and potassium (K+) ions.
- Sodium Influx: This increased permeability leads to a significant influx of sodium ions into the muscle fiber, generating an action potential in the muscle fiber.
- Muscle Contraction: The action potential in the muscle fiber triggers a series of events leading to muscle contraction.
Agents and Diseases that Alter the Function of the Neuromuscular Junction
- Black Widow Spider Venom: The venom of a black widow spider triggers the explosive release of acetylcholine from storage vesicles, not only at the neuromuscular junction but at all cholinergic sites.
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Description
This quiz covers the key concepts related to the neuromuscular junction, focusing on the connection between motor neurons and muscle fibers. It outlines the sequence of events that occur when an action potential arrives at the neuromuscular junction, including neurotransmitter release and receptor binding. Test your understanding of this essential physiological process.
