Final answer:
The formation of a neuromuscular junction involves myotube development, motor neurons reaching the muscle fiber, ACh release, and ion channel activation leading to muscle fiber depolarization and contraction.
Step-by-step explanation:
The process of synapse formation at a neuromuscular junction (NMJ) involves multiple steps: The myotube develops through the fusion of many myoblast cells. When a motor neuron axon reaches the myotube, the NMJ is formed. This specialized chemical synapse allows a motor neuron to transmit a signal to a muscle fiber to initiate contraction. As an action potential travels down the motor neuron axon, it reaches the synaptic end bulbs at the NMJ, triggering the release of the neurotransmitter acetylcholine (ACh). ACh molecules diffuse across the synaptic cleft and bind to ACh receptors on the sarcolemma of the muscle fiber. When ACh binds, ligand-gated ion channels open, allowing cations to flow into the muscle fiber, which depolarizes the muscle membrane (sarcolemma) and initiates muscle contraction. The activities at the neuromuscular junction are similar to those at other synapses, but with some differences in how action potentials translate into muscle contractions.