6.021/Notes/2006-11-15

Myelinated axons

 * Schwann cells form sheath around neuron
 * gap = node of Ranvier
 * Internode (myelinated portion)
 * Node is really small compared with length of internode
 * node is less than 1 micron, internode length is about 1 mm
 * Leaky pipe model
 * At node, Hodgkin-Huxley model for membrane
 * Internodes are completely insulated
 * Saltatory hypothesis
 * Current 'jumps' from node to node
 * Experimental tests
 * Use core conductor model to infer everything
 * measure $$I_o(z,t)$$ for all z and t.
 * data shows decrease in $$I_o$$ along internode so leaky pipe model not true
 * A lot of current is lost along internode
 * Two kinds of derived $$K_m$$
 * Biphasic Hodgkin-Huxley like responses (at nodes)
 * Monophasic outward current at internodes consistent with cable model