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Signals external signals chemical hormones nerotransimtters growth factors cell messengers electrical light mechanical Definition ability for cells to communicate across body New-Branch applies to all cells in body signal transduction = process of transmission from ligand to affect DNA 1. Receptor recognition of ligand 2. Transduction = extracellular message becomes intracellular message secondary messenger potentially can be amplified to many messengers allows for specificity and diversity ie. same receptor different possible messengers and so responces 3. Transmission secondary messenger must reach effector 4. Modulation of effector by activating protein kinase (adds phosphors to proteins) or activation of phophatases (removes phosphors from proteins) 5. Responds to initial stimulus 6. Termination of responce pathways gap junctions protein cylinder allows electrical or chemical passing (in particular Ca) direct cell to cell conduits cardiac and smooth muscles primary sites allows for quick signal transport see types in book excretion to receptor excretion to receptor to signal transduction purpose adapt to changes in environment coordinate actions between cells

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