# 6.021/Notes/2006-11-15

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Jump to navigationJump to search## 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 [math]\displaystyle{ I_o(z,t) }[/math] for all z and t.
- data shows decrease in [math]\displaystyle{ I_o }[/math] along internode so leaky pipe model not true
*A lot of current is lost along internode*

- Two kinds of derived [math]\displaystyle{ K_m }[/math]
- Biphasic Hodgkin-Huxley like responses (at nodes)
- Monophasic outward current at internodes consistent with cable model