To understand how communication occurs between nerves and muscles, we need to arrange the events at the neuromuscular junction in their correct sequence. Here’s the proper order from first to last:
- Arrival of the action potential at the bouton
- Binding of ACh to ACh receptors in the motor end plate
- Generation of action potential in the sarcolemma
Explanation: First, when an action potential reaches the axon terminal (bouton) of a motor neuron, it triggers the release of the neurotransmitter acetylcholine (ACh) from the synaptic vesicles into the synaptic cleft. Following this, ACh binds to its specific receptors located on the motor end plate of the muscle fiber’s sarcolemma (the cell membrane). This binding event causes ion channels to open, leading to a rapid influx of sodium ions, and thus creating a new action potential in the sarcolemma. This entire process is crucial for muscle contraction, as it ensures that the electrical signal is effectively translated into a mechanical response.