Final answer:
The proper sequence for events leading to muscle contraction starts with the opening of voltage-gated calcium channels on the motor neuron, followed by the release and binding of acetylcholine to muscle cell receptors, opening of Na+ channels, T-tubule calcium channels, and then calcium release channels in the sarcoplasmic reticulum.
Step-by-step explanation:
Neuromuscular transmission is a critical process that leads to muscle contraction, and it involves a specific sequence of events related to the activation of ion channels. The correct order leading to muscle contraction is:
- Opening of voltage-gated calcium channels on the motor neuron.
- Acetylcholine, the neurotransmitter, is released and binds to receptors on the muscle fiber, which are acetylcholine receptors.
- Binding of acetylcholine causes the opening of voltage-gated Na+ channels in the muscle cell plasma membrane, leading to depolarization.
- Depolarization then triggers the opening of voltage-gated calcium channels in the T tubules.
- Finally, this opens the calcium release channels in the sarcoplasmic reticulum membrane, releasing calcium into the cytosol and initiating muscle contraction.
The sequence starts with the arrival of an action potential at a motor neuron's axon terminal, causing calcium channels to open. The subsequent influx of calcium ions into the neuron triggers vesicles filled with acetylcholine to fuse with the neuron's membrane, releasing the neurotransmitter into the synaptic cleft. The muscle contraction is initiated when acetylcholine binds to its receptors on the muscle fiber, resulting in sodium channels opening, depolarization of the muscle membrane, opening of T-tubule calcium channels, release of calcium from the sarcoplasmic reticulum, and finally, interaction of the muscle's actin and myosin filaments, powered by ATP, leading to contraction.