G proteins, also known as guanine nucleotide-binding proteins, are a family of proteins that act as molecular switches inside cells, and are involved in transmitting signals from a variety of stimuli outside a cell to its interior.
The alpha subunit, now free to move along the inner membrane, eventually contacts another membrane-bound protein – the “primary effector.” The primary effector then has an action, which creates a signal that can diffuse within the cell. In most cases, a ligand binds to a membrane-spanning receptor protein molecule. Examples being a pain receptor in the skin and a muscle group being an effector. So to clarify: the function of a receptor is to receive sensory information, the function of an effector is to produce an action in response to that information from a receptor. There are two types of effectors, the muscles (also called “motor effectors”) and exocrine glands (also called “secretory efectors”).