Final answer:
Neurotransmitters are the chemical signals detected by receptors on the cell membrane, facilitating communication between neurons and other cells.
Step-by-step explanation:
Signals, in the form of neurotransmitters, are detected via receptors (proteins) on the cell's membrane. The correct answer to the given question is c) Neurotransmitters. Neurotransmitters such as dopamine are chemical signals that are transmitted from neurons to other cellsvia the release of these molecules into the synapses between cells. These signals are fundamental in neurological processes, allowing for communication between neurons and other target cells.
Furthermore, it is important to note that there are different receptors for various signals. For example, the types of hormone receptors include peptide hormone receptors which often function as transmembrane proteins and are also recognized as G-protein-coupled receptors. These typically operate through intracellular second messengers like cyclic AMP (cAMP) or calcium (Ca²+)-calmodulin system. The hormone receptors are critical for mediating changes within target cells and initiating signaling pathways when hormones are present.