Final answer:
When a stimulus affects a motor neuron, it changes the permeability of the cell membrane to ions, such as Na+. This leads to an electrical event called an action potential, which serves as a cellular signal. Communication between nerves and muscles involves the release of neurotransmitters, which bind to sodium channels on the motor end plate.
Step-by-step explanation:
The effect of a stimulus on a motor neuron involves changes in the permeability of the cell membrane to ions. Specifically, if the permeability to Na+ ions changes, they will enter the cell, causing a change in the voltage. This electrical event is called an action potential and serves as a cellular signal.
Communication between nerves and muscles occurs through neurotransmitters, where action potentials in neurons trigger the release of neurotransmitters into the synaptic cleft, binding to receptor molecules on the motor end plate. These receptor molecules are actually sodium channels that open upon receiving the neurotransmitter signal, allowing the passage of Na+ ions into the cell.