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6-Action Potential Figs BW

Ion channel is not uniformaly distributed in myelin

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Unformatted text preview: in myelin as in unmyelin. the V-GATED sodium channels are concentrated in node of ranvier. the Vgated potassium channel are in paranodal region (next to the node). in internode there's no ion channel. when you depolarize, sodium open, AP move down. current don't leak out because multiple layers of myelin sheath increase resistance of axon and lower capacitance (can't store charge because 2 conducting element (ecf and icf) are very far as oppose to close together (very little charge is store in that area). Internodal concentrate the current to nodal area, generate a new AP (jumps node to node). -in myelinated axon, especially big one, big axon+thick myelin sheath, can conduct much more efficiently than biggest of unmyelinated axon. Myelinated Axons: Saltatory Conduction Node of Ranvier Internode Channelopathies Incomplete inactivation of Na+ channel Na+ Channels • Hyperkalemic periodic paralysis • Forms of epilepsy Ca2+ Channels muscle weakness Autoimmune destruction of presynaptic Ca+2 channels kidney disease. hypokalemic (normally high potassium will depolarize, raising extracellular potassium depolarize (make Ek positive, see nerst equation) the heart and kill people with the lethal injection) depolarization should lead to activation and inactivation. inactivation part is deficient, prolong activation of muscle cell lead to paralysis • Lambert-Eaton myasthenic syndrome • Hypokalemic periodic paralysis Abnormal ryanodine • Malignant hyperthermia K+ Channels receptor (Ca+2 release channel in SR) nurse: calcium is release from ER. these ER muscle cell called SR. v-gated calcium channel stimulate muscle contraction. here, excess calcium ion b/c channel open but don't close. muscle contracts too long, body temperature go up. • Long Q-T syndrome (most types) Cl- Channels • Myotonia congenita • Cystic fibrosis Defective CFTR skeletal muscle have high resting cloride potential. but here the refractory period is too much (Cl- channel)...
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