The electric potential, measured in millivolts (mV), produced by depolarization of the end plate at a neuromuscular junction in response to stimulation by the motor neuron. The depolarization results from release of excitatory neurotransmitter molecules, which activate receptors in the postsynaptic membrane, causing transient opening of ion channels and allowing cations to flow briefly through the membrane. In vertebrate skeletal muscle a single EPP, typically about 10–20 mV in amplitude, triggers an action potential in the muscle fibre, which propagates through the fibre causing it to contract.