Difference between Neuromodulators & Neurotransmitters

Per Pathophysiology: The Biologic Basis for Disease in Adults and Children, third edition, by Kathryn L. McCance and Sue E. Heuther, bradykinin is a plasma protein that is a primary kinin in the kinin system. In low amounts it causes dilation of vessels and interacts with prostaglandins to induce pain, causes extravascular smooth muscle contractions, increase vascular permeability and increase leukocyte chemotaxis. It is primarily important in the inflammatory response. With pain, particularly where there has been tissue injury, neurotransmitters are released. Neurokinin A is one of these neurotransmitters that is released from peripheral pain receptors at the point of tissue injury and it promotes the spread of pain locally (neurotransmission activity). Prostaglandin and histamine are also released as a result of injury. Nociceptors in the injured area are the nerve endings that are responsible for detecting and transmitting pain impulses. McCance and Heuther go on to say that bradykinin, in particular, acts as a neuromodulator though interaction with the nociceptors by depolarizing adjacent nociceptors. So, that is where you get the opposite action of the bradykinin and how it is both a neurotransmitter and a neuromodulator. It has to do with the underlying physiology of how bradykinin interacts with the other substances around it. Potter & Perry just didn't get more deeply into the physiology of how bradykinin interacts with other substances to produce both neurotransmission and neuromodulation.

You are welcome. It is likely that you won't get tested over this. But, in case you are, you now know why a bradykinin does both jobs.