No abstract

SUMMARY1. In micro-electrode recordings from the human peroneal and tibial nerves, the responses of thirty-two primary spindle endings, thirteen secondary spindle endings and three Golgi tendon organs were studied during vibration of the tendons of the receptor-bearing muscles in the leg. The amplitude of the applied vibration was 1-5 mm and the frequency was varied from 20 to 220 Hz. As checked with e.m.g. and torque measurements, the muscles of the leg were relaxed during the sequences analysed.2. Providing that the vibrator was accurately applied, all endings responded with discharges phase-locked to the vibration cycles, the discharge rates being at the vibration frequency or at subharmonics of that frequency. The response to vibration was of abrupt onset and offset, was maintained for the duration of vibration, and was not subject to fluctuation with changes in attention or with remote muscle contraction.3. The maximal discharge rate that could be achieved varied from one ending to the next, and increased with the length of the receptor-bearing muscle. For endings driven at their maximal rate an increase in vibration frequency produced a decrease in discharge rate as the ending changed to a subharmonic pattern of response. The converse occurred on decreasing vibration frequency.' 4. For any given muscle length, primary endings could generally be driven to higher rates than secondary endings but there was a wide range of responsiveness within each group and a significant overlap between the groups. At medium muscle length, the most responsive primary endings could be driven up to 220 Hz but secondary endings did not reach discharge rates higher than 100 Hz. 5. With combined vibration and passive movements, primary endings

DELIUS, W., K.-E. HAGBARTH, A. HONGELL and B. G. WALLIN. General characteristics of sympathetic activity in h u m a n muscle nerves. Acta physiol. scand. 1972. 84. 65-81.Multiunit sympathetic activity was recorded from muscle nerve fascicles in the median or peroneal nerve of resting, relaxed human subjects. The impulses, which were reversibly abolished by a sympathetic ganglion blocking agent, were grouped in the pulse rhythm, and series of such pulse rhythmic bursts of impulses regularly appeared during spontaneously occurring blood pressure reductions, whereas temporary blood pressure elevations were associated with neural silence. The findings agree with the notion that the sympathetic muscle nerve activity recorded consists of vasoconstrictor impulses, the outflow of which is modulated by a strong phasic and tonic inhibitory baroreflex influence. The reflex delay from an arterial pulse wave to the corresponding inhibition of efferent sympathetic activity was 0.9-1.4 seconds, depending on the recording site. Several stimuli, such as sudden chest compression, a rapid deep breath or an electrical shock against the skin, caused a transient inhibition of the sympathetic discharges lasting a few seconds.

SUMMARY1. Recordings of multiunit sympathetic activity were made from human nerve fascicles supplying hairy and glabrous skin of the extremities in healthy subjects exposed to different ambient temperatures. Sudomotor and vasomotor events accompanying the neural activity were monitored by simultaneous recordings of electrodermal and pulse plethysmographic events (Pleth) in the neural innervation zones.2. By exposing the subject to warm (43 00) or cold (15 00) environments, it was possible to obtain a selective activation of either the sudomotor or the vasoconstrictor neural system, respectively, with suppression of spontaneous activity in the other system.3. Bursts of both vasoconstrictor and sudomotor nerve activity were found to occur at certain preferred intervals which were integer multiples of a period of about 0-6 sec (100 cycles/min). With high sudomotor or vasoconstrictor tone the 100 cycles/ min rhythm was prominent but with decreasing tone slower subharmonic rhythms prevailed. Respiratory rhythms were also discerned as well as slower rhythms attributable to oscillatory tendencies in thermoregulatory servos.4. Vasoconstrictor bursts had longer mean duration than sudomotor bursts, a finding attributed to a slower conduction velocity of vasoconstrictor as compared to sudomotor impulses.

SUMMARY1. In human subjects, vibration of amplitude 1-5 mm and frequency Hz was applied to the tendons of muscles in the leg to examine the effects on the discharge of primary and secondary endings during manoeuvres designed to alter the level of fusimotor drive.2. In four experiments, the peroneal nerve was completely blocked with lidocaine proximal to the recording site in order to de-efferent spindle endings temporarily. The responses to muscle stretch and vibration, as seen in multi-unit recordings and in single unit recordings, were similar during the block as in the relaxed state prior to the block. Thus, these experiments provided no evidence of a functionally effective resting fusimotor drive.3. The responses to vibration of nine primary endings and four secondary endings were examined during isometric voluntary contractions of the receptor-bearing muscles. Providing that the endings were responding submaximally in the relaxed state, voluntary contraction enhanced the response to vibration, suggesting co-activation of the fusimotor system sufficient to compensate for mechanical unloading. Unloading effects were observed during contractions of neighbouring synergistic muscles, indicating a close spatial relationship between the co-activated skeletomotor and fusimotor outflows.4.