 In this video, I will define intracellular signaling and intracellular signaling and provide examples of each. Cell signaling refers to the communication processes that regulate the function of cells, and this cell signaling is communication at the chemical level. This cell signaling is a chemical signal that can regulate the function of cells, for example activating or inhibiting enzymes to regulate metabolic pathways or controlling the production of proteins by regulating transcription of genes and then translation of the resulting mRNA. Cell signaling can control the cell cycle and regulate cell division to control growth of tissues. Cell signaling can alter membrane permeability, for example opening or closing ion channels. Cell signals can be categorized as either intracellular or intracellular. Intercellular signaling refers to communication between cells, for example hormones and neurotransmitters are intracellular signals, chemical messages that are released by a signaling cell that bind to receptors in a target cell in order to regulate the functions of the target cell. In contrast, intracellular signaling refers to chemical communication within the target cell. When an intracellular signal binds to a receptor, that receptor can then produce an intracellular signal. An example of an intracellular signal is cyclic AMP. Cyclic AMP or cyclic adenosine monophosphate is produced from ATP by the enzyme adenylyl cyclase. So a hormone can stimulate a receptor in the surface of a cell and that receptor can then activate the enzyme adenylyl cyclase to produce cyclic AMP as a second messenger that will then serve as a chemical signal inside of the cell to regulate the functions of that cell. One example of a function that's influenced by the intracellular signal cyclic AMP is the force of contraction of cardiomyocytes in the heart. Cyclic AMP can stimulate opening of calcium ion channels leading to increased contractility, increased force of contraction of the heart muscle. Another example of intracellular signaling is shown in the bottom right here where a hormone could bind to a receptor and then the receptor and hormone form a complex that enters the nucleus and functions as a transcription factor in order to activate the transcription of a gene, which will then be translated to produce a protein. Another example of an intracellular signal is epidermal growth factor. The epidermis is the superficial layer of the skin and epithelial tissue that forms that superficial layer. It's a tissue that's formed from many cells that are tightly packed together forming a sheet of cells. Epidermal growth factor is an intracellular signal, a growth factor that will stimulate mitotic cell division or cell proliferation in order to stimulate tissue growth. When epidermal growth factor binds to the receptor on the surface of cells, that receptor will then activate an intracellular signal known as the extracellular signal regulated kinase, phosphorylation cascade. Extracellular signal regulated kinase is abbreviated ERK, or ERK we pronounce ERK. So the ERK phosphorylation cascade is a series of enzymes that become activated by phosphorylation and then stimulate the phosphorylation of other proteins that will ultimately regulate the transcription and translation of the cyclin genes to produce cyclin proteins that speed up the cell cycle, stimulating mitotic cell division.