Final answer:
The neuromuscular junction is the location where a motor neuron stimulates a muscle cell, through the release of acetylcholine which binds to receptors on the muscle fiber, initiating contraction.
Step-by-step explanation:
The place where a motor neuron stimulates a muscle cell is called the neuromuscular junction (NMJ). This specialized synapse is where the axon terminal of the motor neuron releases neurotransmitters, specifically acetylcholine (ACh), to signal the muscle fibers to contract. The acetylcholine then diffuses across a small gap called the synaptic cleft, binding to ACh-receptors on the muscle fiber's sarcolemma.
The release of ACh at the NMJ leads to the opening of ligand-gated ion channels, which causes depolarization of the sarcolemma, and ultimately results in muscle fiber contraction. Each nerve impulse at the NMJ assures contraction of the muscle fiber, though the frequency of these impulses can affect the strength and number of contracting fibers.