1 N5315 Advanced Pathophysiology Altered Cellular Function and Cancer Module Core Concepts and Objectives with Advanced Organizers Cellular Physiology 1. Analyze the steps of the action potential (allows for electrical communication down a neuron). I. Stimulus needed to fire an action potential. The stimulus causes STIMULUS GATED Na+ Channels to open, causing sodium to rush into the membrane potential, increasing the membrane potential to threshold (-55 mV) II. If threshold is reached, voltage gated Na+ channels open and sodium rushes in membrane potential becomes more positive (30 mV). III. Sodium channels shut IV. Voltage gated potassium channels open Potassium rushes out, and membrane potential drops below the resting potential, but then returns to normal resting potential V. Potassium gates close VI. Sodium potassium pump re-establishes resting membrane potential. 2. Discuss how the action potential is altered by calcium and sodium imbalances and the clinical significance Topic Describe the Action Potential How is the action potential altered by a potassium imbalance? How is the action potential altered by a calcium imbalance? Action Potential Physiology The membrane potential of an active neuron. One that is conducting an impulse. The process of conducting an impulse (action potential) involves a stimulus that activates the neuron the neuron depolarizes (A net movement of sodium into the cell, and the membrane potential decreases, or “moves forward” from negative to zero… the depolarized cell is more positively charged and polarity is neutralized) then repolarizes (the negative polarity of the resting membrane potential is reestablished (-70 to -80 mV)) The action potential carries signals along the nerve or muscle cell and conveys information from one cell to another. Hypokalemia affects resting membrane potential of cells. As the extracellular potassium is depleted, the intracellular potassium diffuses out of the cell easily, which causes the cell to be hyperpolarized (more negative). A cell which is normally -90mV becomes more negative (- 100mV). This causes the cell to be less likely to depolarize and transmit impulses. This causes a decrease in neuromuscular excitability and leads to weakness, smooth muscle atony, paresthesias and cardiac dysrhythmias. Hyperkalemia If the ECF potassium increases without any change in the ICF potassium levels, the resting membrane potential of the cell becomes more positive (normal RMP of -90 mV may now be -80mV). The cell is said to be hypo- polarized. The Cells are more excitable and conduct impulses more easily and quickly. Therefore, the person will have PEAKED T WAVES on EKG. As potassium rises the resting membrane potential will become more positive and it will eventually become equal to the threshold potential (the point at which depolarization must reach in order to initiate an action potential— transmit the impulse occurs when the cell has depolarized by 15 to 20 mV). If the resting membrane potential equals the threshold
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- Fall '15
- Apoptosis, Module 1, cells, cellular injury