The three stages of cell signaling are reception, transduction and response. According to Hartnell College, humans are constantly receiving and interpreting signals from the environment in the form of light, heat, odors, touch and sounds.
The cells of the human body are also receiving signals from other cells in the body. These signals are important to keep cells alive and well to ensure that events such as cell division and differentiation occur. The signals are mostly chemicals found in the extracellular fluids around the cells, also called ligand. These fluids can come from distant locations in the body or from nearby cells and can even come from the same cell.
In the reception stage, membrane receptors bind with a signal molecule or ligand, causing the production of a second signal, which causes a cellular response. These receptors transmit information from the extracellular environment to the inside of the cell by changing shape or joining another protein molecule once a specific ligand binds to it. Examples of membrane receptors are G Protein-Coupled receptors and Receptor Tyrosine Kinases. Intracellular receptors can be found inside the cell in the cytoplasm or the nucleus of the cell. Chemical messengers that are small pass through the plasma membrane and bind to the intracellular receptors. Once the signal binds and is activated the receptor can initiate a cellular response.