Topic: Conduction and transmission of impulse, mechanism of contraction, neuromuscular transmission
Question: Give the sequence of events that occurs during transmission of nerve impulse through neuromuscular junction.
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The transmission of a nerve impulse through the neuromuscular junction involves several sequential events:
- Action potential in the presynaptic neuron: The process begins with an action potential in the presynaptic neuron (the motor neuron), which travels down its axon towards the neuromuscular junction.
- Release of neurotransmitters: When the action potential reaches the axon terminal, it triggers the release of neurotransmitters (acetylcholine) from synaptic vesicles into the synaptic cleft.
- Binding of neurotransmitters to receptors: The neurotransmitters then bind to specific receptors (nicotinic acetylcholine receptors) on the postsynaptic membrane (the muscle fiber membrane), which triggers a series of events that lead to the generation of an action potential in the muscle fiber.
- Generation of an action potential in the muscle fiber: The binding of neurotransmitters to receptors causes the opening of ion channels in the muscle fiber membrane, which allows an influx of positively charged ions (sodium and potassium) into the muscle fiber. This depolarizes the muscle fiber membrane, triggering an action potential that propagates along the muscle fiber.
- Contraction of the muscle fiber: The action potential in the muscle fiber triggers the release of calcium ions from the sarcoplasmic reticulum (a specialized type of endoplasmic reticulum found in muscle fibers), which initiates the process of muscle contraction.
- Termination of the signal: The neurotransmitters are quickly removed from the synaptic cleft by enzymes (acetylcholinesterase) that break them down, or by reuptake into the presynaptic neuron. This terminates the signal and allows the muscle fiber to relax.
