Using light- and electron-microscopic techniques, a quantitative histological study of the rat saphenous nerve has been carried out. The distribution of myelinated fibre diameters was bimodal; while that of the unmyelinated axons was unimodal. The variation of myelin sheath thickness with axon diameter was non-linear; two straight lines were found to fit the data best. The variation of g (axon diameter/total fibre diameter) with total fibre diameter was also nonlinear, being best fitted by two lines – one straight, the other slightly curved. The number of unmyelinated axons per Schwann cell process was examined. The ratio of unmyelinated axons to myelinated fibres was 3.42:1.

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Five far-field components were identified preceding the cortical wave in response to the stimulation of the A beta fibers of the sural nerve. When A delta activity was also included in the afferent volley, a second cortical wave and additional far-field potentials were recorded. Upon blocking the A beta fiber activity and thus isolating the peripheral input to A delta fibers alone, the initial cortical wave and the far-field potentials preceding it disappeared completely, leaving the A delta evoked potentials intact.

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