"Resistance," R, implies restraint of movement; "conductance," g, connotes ease of passage and is a preferred term for reference to ion transport. The two terms are reciprocally related; i.e.
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The main "fabric" of the nerve membrane is a lipid bilayer that is essentially impermeable to the water-soluble ions. In that bilayer are embedded many proteinaceous hydrophilic conductance channels, through which the water-soluble ions can move between the axon core and the external medium. These pathways are lumped together as the resistance RM in Fig. 2. In a surface view of the membrane (Fig. 3), the channels are depicted as holes connecting the inside of the neurone to the extracellular solution.
Figure 3. Ion conductance channels of the membrane.
"Resistance," R, implies restraint of movement; "conductance," g, connotes ease of passage and is a preferred term for reference to ion transport. The two terms are reciprocally related; i.e.
Depending on the membrane potential, the channels can be open and allow passage of current (open circles in Fig. 3) or they can be closed (filled circles). The number of channels that are open and the frequency and duration of their being open determine the amount of specific ion current.
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