Mechanism of Conduction


Na ion influx에 따라 옆의 흥분되지 않은 막에 depolarizing electrotonus제공
propagation of excitation by electrotonic coupling

Membrane currents during the conducted action potential

AP: from right to left
A: left쪽으로 막을 depolarize(gNa 증가), electrotonic spread of + ions
C: right 쪽의 막은 depolarization prevented by high gK
(if gK is relativel low or some depolarizing effects---> repetitive 흥분)

Factors determining conduction velocity
amplitude of the inward Na+ current
(Na+ 농도 낮춤, enhanced inactivation of the Na+ system, local anesthetics
---> Na+ influx저하--> 전도속도 감소)

resistance and the capacitance of a unit area of membrane: 대체로 동일
Electrotonic spread: fiber diameter가 주로 결정
membrane area: proportional to diameter
cross-sectional area: " to the square of the diameter
증가된 fiber diameter---> cross sectional area에 의해 결정되는
longitudinal resistance가 감소--->
more extensive spread of the electrotonic currents
(increase in length constant): predominant
membrane diameter의 증가--> membrane capacitance가 증가-->
conduction velocity 감소: minor
CV: fiber diameter의 square root로 증가.

Conduction in myelinated axons

Saltatory conduction in myelinated fiber
nodes of Ranvier
conduction time through the internode: practically zero
internode: electrotonic spread without decrement
delay occurs only at nodes: to reach threshold and elicit AP
Na+ channel density가 100X than unmyelinated fibers
CV: above 3m/sec, myelinated fibers










BRAIN FACTS