Table 1.

Dextran penetration (in μm) in live-injected fibers

Tracer	Time (min) total (live + prep)	Calculated			Measured	n
		1	2	3
3 kDa	30 (0 + 30)	440	409	2.8	1.0 ± 0.9	14
	60 (30 + 30)	621	590	4.0	3.2 ± 2.8	16
	90 (60 + 30)	762	731	4.9	5.4 ± 4.2	45
70 kDa	30 (0 + 30)	153	122	1.0	0.4 ± 0.3	14
	60 (30 + 30)	216	185	1.4	1.3 ± 0.9	16
	90 (60 + 30)	264	233	1.7	1.8 ± 1.3	45
	150 (120 + 30)	341	310	2.2	5.9 ± 2.8	24

Calculated and measured dextran tracer penetration in live fibers. Tracer penetration through pathways 1, 2, and 3 in a fiber assumed to have a paranode 5 μm in diameter and 5 μm long with transverse bands oriented at 8° to the transverse plane and with paranodal loops spaced at 0.1 μm intervals. Average measured penetration approximates calculated penetration through pathway 3 but differs from that through pathways 1 or 2 by approximately two orders of magnitude. Each calculated value represents the axial distance (μm) moved on one side of a node in the paranode plus distance in the internode. Each Measured value represents apparent axial extent of tracer penetration (± SD). n, Number of paranodes measured.