N5315 Advanced Pathophysiology Altered Cellular Function and Cancer Module Core Concepts and Objectives with Advanced Organizers Cellular Physiology1. Analyze the steps of the action potential. ● Sodium permeability increases, sodium ions move into the cell increasing positivity, depolarization is occurring, action potential threshold is reached as cell becomes more positive, potassium permeability increases, potassium ions leave the cell, repolarization isoccurring, resting membrane potential is reestablished.· The action potential carries signals along the nerve or muscle cell and conveys information from one cell to another.· When a resting cell is stimulated with voltage the membrane becomes permeable to sodium.· Movement of sodium into the cell, the membrane potential decreases, moves to a negative or zero is known as depolarization. Depolarized cells are positively charged.· To generate an action potential and the resulting depolarization is known as threshold potential. It happens when the cell has depolarized by 15-20 millivolts. When the threshold ismet the cell continues to depolarize with no further stimulation. This makes the sodium rush out of cell causing the membrane potential to reduce to zero and become positively (depolarization). This rapid reversal in polarity results in action potential.· Repolarization is negative polarity of the resting membrane potential. Membrane permeability to sodium decreases, and potassium increases with outward movement of potassium. This makes the membrane potential more negative.· During most of the action potential the plasma membrane cannot respond to any additional stimulus is known as absolute refractory period. Its related to changes in sodium.· If potassium increases, a stronger stimulus can evoke an action potential is relative refractory period.· A membrane potential more negative than normal, requires a larger stimulus to reach the threshold potential is hyperpolarized (less excitable). occurs when the membrane is repolarizing.· A membrane that is more positive than normal, needs smaller stimuli to reach threshold potential is hypopolarized (more excitable than normal). 2. Discuss how the action potential is altered by calcium and sodium imbalances and the clinical significance · Na has a greater concentration in the ECF. When a neuron is excited by a stimulus, the stimulus-gated Na+ channels open allowing Na+ to move intracellularly. This moves theresting membrane potential of -70mV more towards 0. Once the threshold potential is reached (-59mV) the voltage gated Na+ channels open allowing for more Na+ to move into the cell and complete the depolarization to a maximum of +30mV. If the depolarization does not reach a minimum of -59mV (threshold potential) the voltage gated Na+ channels will not open and the cell will simply repolarize to -70mV without generating an action potential.· Hyponatremia: Cellular swelling and deficits of intracellular Na alter the ability of cells to depolarize and repolarize normally. Causes neurological changes headaches, lethargy, and seizures.· Hypernatremia: Na is largely in the ECF, increase concentration of Na causes intracellular dehydration and hypervolemia. Causes hypotension, tachycardia, thirst.· Hypercalcemia decreases cell permeability to sodium. This causes the threshold potential to become more positive and is further away from the membrane potential. It takes more of a stimulus to initiate an action potential. The cells are far less excitable and do not initiate action potentials. This leads to weakness, hyporeflexia, fatigue, lethargy, confusion, encephalopathy, a shortened QT segment and depressed widened T waves on EKG. · Hypocalcemia- calcium deficits causes partial depolarization of the nerves and muscle as the threshold potential becomes more negative and approaches resting membrane potential (hypopolarization). A smaller stimulus is needed to start the action potential. This means the cells are more excitable. This results in tetany, hyperreflexia, paresthesias, prolonged QT interval, seizures, muscle spasms, laryngospasm. Topic Describe the Action PotentialHow is the action potential altered by a potassium imbalance?How is the action potential altered by acalcium imbalance?Action Potential Physiologyis the membrane potential of anactive neuron.One that is conducting animpulse. The process of conducting animpulse (action potential) involves a stimulus that Hypokalemia causes a more negative resting membrane potential therefore the cell is more difficult to excite. Because potassium contributes to the repolarization phase of the action potential, hypokalemia delays ventricular repolarizationand the frequency of action potentialsHypercalcemia causes a higher action potential threshold causing a more difficult excitable action potential.Hypercalcemia decreases the cell permeability to Na+ which makes the threshold potential more positive and further away from theactivates the neuron → the neuron depolarizes → then repolarizesOnce the cell is more positively charged, the sodium channels open and sodium flows into the cells. Membrane potential is near zero. The neuron repolarizes (becomes more negatively charged), potassium channels open.Causes: weakness, smooth muscle atony, paresthesias, cardiac dysrhythmiasHyperkalemia affects the resting membrane potential. the resting membrane potential of the cell becomes more positive. A normal RMP of -90mv may now be -80mv. The cell is said to be hypo-polarized. The cells are more excitable and conduct impulses more easily and more quickly.; therefore, the person will have peak T waves on EKG. As potassium rises the resting membrane potential will continue to become more positive and it will eventually become equal to the threshold potential. The threshold potential is the point at which depolarization must reachin order to initiate an action potential (transmit the impulses). If the resting membrane potential equals the threshold potential, an action potential will not be generated and cardiac standstill will occur. Paralysis and membrane potential. Takes a stronger stimulus to initiate theaction potential. Cellsare less excitable.Causes: weakness, hyporeflexia, fatigue, lethargy, confusion, encephalopathy, shortened QT segment, depressed widened T-waves.When the action potential reaches the axon ending, it causes another ion (calcium, Ca++) to enter the cell, which in turn causes the
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