the hormone knocks on the door, but this is the guy who actually runs through the house yelling.
means a small intracellular molecule that relays and amplifies a signal from a receptor on the cell surface to targets inside the cell.
from coined by earl sutherland in the 1950s-60s while studying how adrenaline raises blood sugar without ever entering the cell — adrenaline was the first messenger, cyclic amp was the second, and the name stuck when he won the 1971 nobel prize for it.
cyclic amp — mediates adrenaline and glucagon signaling in liver cells
calcium ions — trigger muscle contraction within milliseconds of nerve signal
ip3 and dag — split from a membrane lipid to open calcium channels
cyclic gmp — drives the light response in retinal rod cells