Receptor: A receptor is a protein located on the surface of cells that binds to specific signaling molecules (ligands), initiating a response within the cell.
Hormone: Hormones are specialized signaling molecules produced by glands in multicellular organisms. They travel through the bloodstream to target cells and regulate various physiological functions.
Neurotransmitter:Neurotransmitters are signaling molecules released by nerve cells (neurons) to transmit signals across synapses to neighboring neurons or target cells. They play crucial roles in communication within the nervous system.