8-31-09 The Action Potential

8-31-09 The Action Potential - The Action Potential The...

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Unformatted text preview: The Action Potential The Action Potential Dr. McKemy 8/31/2009 Na+ channels open K+ channels open Nomencalture of the Action Potential Nomencalture of the Action Potential The squid led the way! The squid led the way! The Voltage Clamp Technique The Voltage Clamp Technique Flow of current during voltage steps Flow of current during voltage steps Identified two­types of voltage­dependent currents. ◦ Early and late currents. ◦ Different voltage­dependencies Current produced at different potentials Current produced at different potentials Early currents are dependent upon Na+ Pharmacology separates the components into Na+ and K+ components Early and late currents Early and late currents Mepotential mbrane conductance changes underlying the action Mepotential mbrane conductance changes underlying the action are time­ and voltage­dependent Mathematical reconstruction of the action potential Mathematical reconstruction of the action potential Refractory Period Refractory Period In the resting state, most Na+ channels are closed. ◦ K+ channels are open. ◦ Negative-inside. If Na+ channels open, the resulting influx of Na+ overwhelms the efflux of K+. ◦ Net inward movement of (+)charges. n Also leaves behind Cl-. ◦ Now the cytosolic face of the membrane has a net (+)-charge. n Depolarized. n Moved towards ENa. Axon contains Na+ and K+ channels that are gated by changes in MP. ◦ In addition to resting K+ channels. Coordinated opening and closing of Na+ and K+ Coordinated opening and closing of Na channels Regenerative nature of the AP Regenerative nature of the AP Propagation of an action potential Propagation of an action potential Role of Na+ and K+ channels Role of Na Can the AP be made to conduct faster? Role of Na+ and K+ channels Role of Na Passive current flow in an axon Passive current flow in an axon Saltatory AP conduction along a myelinated Saltatory AP conduction along a myelinated axon Saltatory AP conduction along a myelinated axon Saltatory AP conduction along a myelinated axon Myelinated axons conduct faster Myelinated axons conduct faster Myelinated axons conduct faster Myelinated axons conduct faster Multiple Sclerosis (MS) is an inflammatory autoimmune disorder that destroys the myelin sheath. ◦ De-myelination and inflammation along axonal pathways. ◦ Symptoms: n Monocular blindness ◦ Lesions in the optic nerve n Double vision ◦ Lesions in the medial longitudinal fasciculus n Weakness or paralysis ◦ Lesions in the corticospinal tracts n Altered somatic sensations ◦ Lesions of somatosensory pathways. n Dizziness ◦ Lesions in the vestibular pathways Multiple sclerosis and myelination Multiple sclerosis and myelination ...
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This note was uploaded on 04/18/2010 for the course BISC 421 at USC.

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