N5315 Advanced Pathophysiology Action Potentials I. The action potential is a process by which excitable cells transmit information to one another. This process typically occurs in nerve cells and all types of muscle cells. An alteration in the action potential may result from neurologic disease, muscle disease or electrolyte imbalances. II. In order to understand the action potential, it is essential that you have a working knowledge of the cell membrane and transport systems. I will review some basics now. III. Cell membranes are responsible for controlling the composition of the space they enclose. a. The cell membrane is responsible for providing structure and protection to the cell, regulating cellular activity by receiving cellular signals, transport into and out of the cell, and cell to cell interactions. The cell membrane is composed of phospholipids, cholesterol and glycolipids. Phospholipids are responsible for repairing the cell membrane by folding in on themselves and forming a sealed compartment. b. The cell membrane is highly permeability to lipid soluble substances such as carbon dioxide, oxygen, fatty acids and steroid hormones. The cell membrane is not very permeable to water soluble substances such as ions, glucose and amino acids. IV. The cell membrane contains protein in it to help maintain cellular homeostasis. a. Transmembrane proteins span the entire width of the cell membrane and are in contact with both the extracellular and the intracellular compartments. These proteins include ligand-binding receptors which bind with hormones or neurotransmitters; transport proteins such as the Na + -K + ATPase, pores, ion channels, cell adhesion molecules and GTP-binding proteins (G proteins). i. The Na + -K + ATPase is the main protein which is responsible for maintaining the correct balance of extracellular Na + and intracellular K + , which is needed for cellular excitation and membrane conductivity. The maintenance of intracellular K + concentration is required for enzyme activity. This is the pump which is highly involved in the action potential. In normal physiology Na + concentration is greatest on the outside of the cell and potassium concentration is greatest on the inside of the cell. It pumps sodium to the ECF and potassium to the ICF. This protein transports 3 molecules of sodium to the ECF and two molecules of potassium to the ICF. This protein is essential to maintaining the ionic
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- Fall '15
- ICF, ECF, excitable cells