Hi there John C - are you still confused!. Perhaps this will help you understand. Here is an example of what receptors can actually do.


Receptors are critical to the life of all cells, whether or not the cell represents an animal, a plant, a fungus, or a bacterium. Every function, response, interaction, pathway, process, and any other term you might think of that concerns the moment-to-moment existence of a cell, is controlled by various receptor/ligand-induced systems.
Human cells need a source of energy in order to maintain life. One such source is the sugar molecule, glucose. All of the materials necessary to utilize glucose are inside the cell. And, in order to obtain glucose we must absorb it in some way from our intestines. There are special receptors, called carrier proteins, within the membrane of cells which line the intestinal "wall". These carrier proteins are specific for glucose and energy is used to pump the glucose into the cells that line the intestines. Through interaction with other kinds of glucose carrier proteins, glucose eventually is deposited into the bloodstream. There, the glucose molecules reach cells throughout the body. Glucose cannot, however, simply diffuse across a cell's membrane and enter the cell. The movement must be facilitated by a cell's response to the hormone, insulin. Insulin receptors on cells, bind to a specific region of the insulin molecule, and this interaction triggers a molecular "wiggling" of the insulin receptor. The result of this slight movement causes a chemical reaction to occur (part of the insulin receptor is actually a kind of special enzyme which transfers phosphate groups). This reaction triggers further specialized reactions within the cell along a very precise activation pathway which ultimately result in the uptake by the cell of glucose.
Another kind of receptor, the acetylcholine receptor, specifically interacts with a chemical substance known as acetylcholine (asseh-teel-ko-leen) and this interaction allows nerve impulses to travel to a muscle and trigger movement of an entire muscle group. Other kinds of receptors in our nasal tissue (olfactory tissue) are connected by nerves to our brain. When certain chemicals react with receptors specific for them, we may experience an automatic withdrawal/avoidance reaction as one result. Our brain interpreted the nerve impulses in such a way as to lead to a "warning". The ability to respond to such a warning signal depends upon our genetic makeup - the genes which lead to all of these kinds of responses. Alternatively, if we possess receptors in our nasal tissues which can bind to molecules emitted by the flower of a lilac bush, we may react pleasurably to this "smell". I know I do.
Therefore, receptors are necessary for many, many things. Without receptors, we'd lead a pretty dull existence. And, although we might not experience pain, either physical or emotional, we'd also be unable to experience any of the joy of life.

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