Final answer:
When a somatic motor neuron releases an action potential, it prompts the release of acetylcholine at the neuromuscular junction, which then binds to receptors on the muscle cell membrane leading to muscle depolarization and contraction.
Step-by-step explanation:
When a somatic motor neuron releases an action potential, it triggers a sequence of events that lead to muscle contraction. This process begins as the action potential travels down the motor neuron's axon to the neuromuscular junction (NMJ). Here, the axon terminal releases the neurotransmitter acetylcholine (ACh), which diffuses across the synaptic cleft and binds to ACh receptors on the motor end plate of the sarcolemma (the muscle cell membrane).
Once ACh binds, it causes an influx of sodium ions through the opened channels. This initiates a change in the resting membrane potential of the muscle cell, leading to depolarization. This depolarization triggers an action potential that moves along the sarcolemma and down the T tubules, causing calcium release from the sarcoplasmic reticulum and ultimately resulting in muscle fiber contraction.