Neuromodulators are chemicals which do not directly activate neurons in the body but act together with neurotransmitters to enhance the excitatory or inhibitory responses of the neurons in order to regulate functions in the body. It is often difficult to differentiate between neurotransmitters and neuromodulators as some chemical messengers (such as endorphins, acetylcholine and glutamate) have properties of both.Baars, B. and Gage, N. (2010). Cognition, Brain, and Consciousness. 2nd ed. Academic Press. Queensland Brain Institute. (n.d.). What are neurotransmitters? [online] Available at: https://qbi.uq.edu.au/brain/brain-physiology/what-are-neurotransmitters [Accessed 19 Nov. 2018]. Erulkar, S. (n.d.). Nervous system. [online] Encyclopedia Britannica. Available at: https://www.britannica.com/science/nervous-system/Active-transport-the-sodium-potassium-pump#ref75855 [Accessed 19 Nov. 2018].