4 Action potentials

Based on this process we say that ac0on poten0als are

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Unformatted text preview: a0on loop 5 1 Res0ng state Undershoot AKA [email protected] ­hyperpolarizaDon An ac0on poten0al travels along an axon as each depolarized patch of membrane causes ionic currents to flow longitudinally along the axon, and these currents depolarize the next patch of membrane. Based on this process we say that ac0on poten0als are ac0vely propagated along axons. Axon Plasma membrane Ac0on poten0al Cytosol Na+ K+ Ac0on poten0al Na+ K+ Fig. 48-11-3 K+ Ac0on poten0al Na+ K+ Some axons are wrapped by glial cells (called Schwann cells in the periphery and oligodendrocytes in the CNS). This wrapping is called myelin, and it greatly speeds up the conduc0on velocity along myelinated axons. The diagram on the lec illustrates myelina0on, and the image on the right is a transmission electron micrograph of a cross ­sec0on through a myelinated axon. Node of Ranvier Layers of myelin Axon Schwann cell Axon Myelin sheath Nodes of Ranvier Schwann cell Nucleus of Schwann cell Fig. 48-12 How does myelin increase conduc0on velocity? 0.1 µm Only membrane at the nodes of Ranvier contains voltage ­gated Na+ and K+ channels, so the signal jumps from node to node. Schwann cell Depolarized region (node of Ranvier) Cell body Myelin sheath Axon Fig. 48-13...
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This note was uploaded on 02/18/2012 for the course BILD 2 taught by Professor Schroeder during the Spring '08 term at UCSD.

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