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Neuromuscular junction: Difference between revisions
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(Created page with "<section begin="pharmacology" /><section begin="physiology" />The '''neuromuscular junction''' (NMJ) is the most important synapse. It’s the synapse between the nervous system and the skeletal muscle. More specifically, it’s the synapse between the axon of the alpha motor neuron in the anterior horn of the spinal cord and the skeletal muscle it innervates.<section end="pharmacology" /> Like all chemical synapses, there is a neurotransmitter and a postsynaptic re...") |
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Because the EPP is much larger than needed to reach threshold, there is a so-called ''safety factor'' of approx. 20 mV. This means that if the EPP were to be reduced for any reason it would still be enough to reach threshold, as long as it wasn’t reduced more than the safety factor. Reduction of EPP is one mechanism of muscle fatigue, which we’ll discuss in topic 8 in physiology 1. | Because the EPP is much larger than needed to reach threshold, there is a so-called ''safety factor'' of approx. 20 mV. This means that if the EPP were to be reduced for any reason it would still be enough to reach threshold, as long as it wasn’t reduced more than the safety factor. Reduction of EPP is one mechanism of muscle fatigue, which we’ll discuss in topic 8 in physiology 1. | ||
== Steps at the neuromuscular junction == | == Steps at the neuromuscular junction == | ||
An action potential travels down the axon of the alpha motor neuron, eventually reaching the presynaptic membrane, which becomes depolarized. This depolarization opens voltage-gated Ca2+ channels on the presynaptic membrane, which allows Ca2+ to flow into the end of the axon. This Ca2+ inflow triggers the release of acetylcholine from the presynaptic vesicles into the synaptic cleft. | <section begin="pharmacology" />An action potential travels down the axon of the alpha motor neuron, eventually reaching the presynaptic membrane, which becomes depolarized. This depolarization opens voltage-gated Ca2+ channels on the presynaptic membrane, which allows Ca2+ to flow into the end of the axon. This Ca2+ inflow triggers the release of acetylcholine from the presynaptic vesicles into the synaptic cleft. | ||
The acetylcholine diffuses across the synaptic cleft and binds to the nicotinic acetylcholine receptors on the motor end plate. The nicotinic acetylcholine receptor is a non-selective cation channel, meaning that when acetylcholine binds to it, the ion channel will open and allow Na+ and K+ to enter the cell. | The acetylcholine diffuses across the synaptic cleft and binds to the nicotinic acetylcholine receptors on the motor end plate. The nicotinic acetylcholine receptor is a non-selective cation channel, meaning that when acetylcholine binds to it, the ion channel will open and allow Na+ and K+ to enter the cell. | ||