What are chemicals that relay, amplify, and modulate signals between a neuron and another cell called?

Neurotransmitters are specific chemical substances that facilitate communication between neurons and other cells, such as muscle cells or other neurons. They are released from the presynaptic neuron into the synaptic cleft and bind to receptors on the postsynaptic cell, which relays, amplifies, and modulates the original signal. This process is essential for transmitting signals across the nervous system and plays a critical role in various physiological processes including mood, perception, and motor function.

The other options represent different biological substances or components. Hormones are signaling molecules produced by glands in the endocrine system and travel through the bloodstream to target organs; they act on a broader scale compared to neurotransmitters. Receptors are proteins located on the surface of cells that receive and bind to neurotransmitters or hormones, but they are not the chemicals themselves. Electrolytes are ions in the body's fluids that are crucial for conducting electrical impulses in tissues but do not function as signaling molecules between neurons. Thus, neurotransmitters are uniquely defined by their role in neuronal signaling.