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This 3 page Class Notes was uploaded by Kelly Wetmore on Tuesday March 1, 2016. The Class Notes belongs to Bio 242 at University of Rhode Island taught by Barbara Van Sciver in Winter 2016. Since its upload, it has received 23 views.
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Date Created: 03/01/16
Sunday, March 6, y Lecture 7 Decremental Property of Graded Potentials Higher density of sodium channels in axon hillock A stimulus causes an increase in the permeability for sodium going into the cell Sodium goes in (positive charge) cases a depolarization with the resting membrane potential (70mV ———> 60mV) • Potassium can leave the cell Effect of stimulus strength on size of graded potential Great strength = greater strength of graded potential Threshold 55mV Voltage for a typical cell is 55mV • Voltage at which many sodium voltage gates open • Closed lower than 55mV EX: 70mV Concept of a Threshold Stimulus A threshold (55mV) sodium goes in Rising Phase Due to Sodium influx 1 Sunday, March 6, y Voltage- +30mV Potassium goes out of the cell (positive charge) More potassium can leak out at resting membrane potential At Peak Voltage gates open for potassium Then potassium reflux occurs Then back down to resting membrane potential (70mV) Action membrane potential conduction in unmyelinated axons Electrotonic currents decay rapidly over as they spread This occurs because such of the current leaks through the unmyelinated membrane Myelin Lipid (nonpolar) Material that surrounds many of the axons in our body A good insulator Schwann cells PNS Oligodendrocytes CNS Formation and organs of myelin sheaths Gaps node of ravier Myelin increases the speed of impulses in the axon 2 Sunday, March 6, y Multiple Sclerosis Autoimmune disease that attacks myelin and leaves scars Scarring slows down the speed of the action potential (sometimes blocks) Axonal Regeneration of PNS Neurons cannot reproduce Schwann cells can reproduce • Regeneration tube guides the slowly growing axon • This cannot happen in the CNS One Way Propagation of Current Why does it only go one way? Na+ voltage gast have 3 confirmations • Open • Closed can be open with stimulation • Closed can’t be opened Refectory Period Absolute cannot be opened (closed) Relative can be opened but needs a stimulus (greater than normal stimulus) 3
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