What initially causes a nerve impulse?

A nerve impulse begins when a stimulus changes the electrical balance across a neuron's membrane. At a synapse, chemical messengers bind to receptors on the receiving neuron, often on its dendrites, and cause ions to move across the membrane. This can start an electrical impulse. Red blood cells, pathogens, and enzymes do not normally initiate nerve impulses in this way.

AI-written and checked against the verified answer.