Conduction velocities and nerve fibre diameters of touch, pain, urinary bladder and anal canal afferents and alpha and gamma-motoneurons in human dorsal sacral roots.

1. Single action potentials were recorded extracellularly at 2 sites from human sacral dorsal nerve roots, and their conduction time measured. Conduction velocity frequency distribution histograms were constructed from afferent and efferent nerve fibres. Conduction velocity distribution peaks could be identified from afferents of mechanoreceptors of the skin, the bladder, the anal canal, of stretch and flow receptors of the urinary bladder, from spindle afferents and from the 3 alpha (extrafusal) and 3 gamma-motoneuron (intrafusal) classes. The electrophysiologically measured roots were removed and morphometrically analysed. Nerve fibre diameter frequency distribution histograms were constructed with respect to 3 myelin sheath thickness ranges. Nerve fibre diameter distribution peaks could partly be correlated to the corresponding conduction velocity distribution peaks. 2. Identified nerve fibre classes, characterized by their group peak values of conduction velocity and fibre diameter were at about 36 degrees C (age 30 years): Spindle afferents: SP1 (60 msec-1/13.2 microns) SP2 (50/12.0?); touch afferents: TO (49 msec-1/13.0 microns), T1 (44/11.2), T2 (39/10.1), T3 (31/9.1), T4 (20/8.3); pain afferents: P (13 msec-1/?); mucosa touch afferents from bladder and anal canal: M (12.5 msec-1/?); bladder afferents from stretch receptors measuring probably mural tension: S1 (42.5 msec-1/?), ST (38/?) and from flow receptors: S2 (12.5/?); alpha-motoneurons: alpha 1 (60 msec-1/13.1 microns) [FF], alpha 11 (?/12.0) [F (int)], alpha 2 (50/10.2) [FR], alpha 3 (37/8.3) [S]; gamma-motoneurons: gamma beta (27 msec-1/7.2 microns), gamma 1 (20/6.7), gamma 2 (15/6.2). 3. Because of the strong temperature dependence of the conduction velocities a calibration of the structure of the velocities, which was almost independent of temperature, is defined by the condition that the alpha 2-motoneurons have the same peak conduction velocity then the secondary spindle afferents (SP2); the T1 touch afferents have about 10% lower velocity values. 4. Touch afferents and alpha-motoneurons had a different velocity-diameter relation, which indicated differences in the myelin sheath thickness and/or membrane properties. The conduction velocities of the touch afferents were more temperature-dependent than those of the alpha-motoneurons. Within the classes of touch afferents and alpha-motoneurons the temperature dependence increased towards smaller class peak values. 5. Through the use of action potential wave form comparisons it was possible to identify action potentials from single nerve fibres in each class of touch afferents (T0 to T4). Activity patterns of single touch units could partly be analysed.(ABSTRACT TRUNCATED AT 400 WORDS)