In a phenomenon known as , many incoming signals produce progressively larger graded potentials in a cell−larger than any single impulse would produce alone.

neurotransmitters

Explanation:

Neurotransmitters are endogenous chemicals that enable neurotransmission. It is a type of chemical messenger which transmits signals across a chemical synapse, such as a neuromuscular junction, from one neuron (nerve cell) to another "target" neuron, muscle cell, or gland cell.

electromagnetic waves travel through space with vacuums. give me brainliest if right.