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- Axelson, Hans W, et al.
(författare)
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Human motor control consequences of thixotropic changes in muscular short-range stiffness
- 2001
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Ingår i: Journal of Physiology. - : Wiley. - 0022-3751 .- 1469-7793. ; 535:Pt 1, s. 279-288
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Tidskriftsartikel (refereegranskat)abstract
- The primary aim of the present study was to explore whether in healthy subjects the muscle contractions required for unrestrained voluntary wrist dorsiflexions are adjusted in strength to thixotropy-dependent variations in the short-range stiffness encountered in measurements of passive torque resistance to imposed wrist dorsiflexions.After a period of rest, only the first movement in a series of passive wrist dorsiflexions of moderate amplitude exhibited clear signs of short-range stiffness in the torque response. During analogous types of voluntary movements, the extensor EMG during the first movement after rest showed a steep initial rise of activity, which apparently served to compensate for the short-range stiffness.The passive torque resistance to minute repetitive wrist dorsiflexions (within the range of short-range stiffness) was markedly reduced after various types of mechanical agitation. During analogous low-amplitude voluntary wrist dorsiflexions the extensor EMG signals were weaker after than before agitation.Mechanical agitation also led to enhancement of passive dorsiflexion movements induced by weak constant torque pulses. In an analogous way, the movement-generating capacity of weak voluntary extensor activations (as determined by EMG recordings) was greatly enhanced by mechanical agitation.The signals from a force transducer probe pressed against the wrist flexor tendons - during passive wrist dorsiflexions - revealed short-range stiffness responses which highly resembled those observed in the torque measurements, suggesting that the latter to a large extent emanated from the stretched, relaxed flexor muscles. During repetitive stereotyped voluntary wrist dorsiflexions, a close correspondence was observed between the degree of short-range stiffness as sensed by the wrist flexor tension transducer and the strength of the initial extensor activation required for movement generation.The results provide evidence that the central nervous system in its control of voluntary movements takes account of and compensates for the history-dependent degree of inherent short-range stiffness of the muscles antagonistic to the prime movers.
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| 2. |
- Bini, G, et al.
(författare)
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Regional similarities and differences in thermoregulatory vaso- and sudomotor tone.
- 1980
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Ingår i: Journal of Physiology. - : Wiley. - 0022-3751 .- 1469-7793. ; 306, s. 553-65
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Tidskriftsartikel (refereegranskat)abstract
- 1. Skin nerve sympathetic activity was recorded simultaneously from the following pairs of nerves: left and right median, median and peroneal, left and right peroneal, posterior cutaneous antebrachial and superficial radial, posterior cutaneous antebrachial and median. The recordings were performed on healthy subjects exposed to different ambient temperatures. Electrodermal responses and pulse plethysmograms were recorded from the neural innervation zones. 2. Vasoconstriction impulse bursts recorded simultaneously from the median and peroneal nerves during exposure to a cold environment showed a striking similarity with respect to the timing and strength of individual bursts. A similar strong correlation was observed also among sudomotor bursts recorded simultaneously from the posterior cutaneous antebrachial and superficial radial nerve during exposure to a warm environment. 3. On some occasions, such as during exposure to a moderately warm environment or emotional stress, a temporal correlation was also observed between vasoconstrictor bursts recorded from the median and sudomotor bursts recorded simultaneously from the posterior cutaneous antebrachial nerve. 4. The double nerve recordings provided evidence that in the distal glabrous skin areas reflex thermoregulatory functions are mainly executed via vasoconstrictor fibres whereas sudomotor fibres are brought into action only at relatively high temperature. On the contrary, in the hairy skin on the dorsal side of forearm and hand reflex thermoregulation is to a large extent executed via sudomotor fibres.
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| 3. |
- Bini, G, et al.
(författare)
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Thermoregulatory and rhythm-generating mechanisms governing the sudomotor and vasoconstrictor outflow in human cutaneous nerves.
- 1980
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Ingår i: Journal of Physiology. - : Wiley. - 0022-3751 .- 1469-7793. ; 306, s. 537-52
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Tidskriftsartikel (refereegranskat)abstract
- 1. 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 degrees C) or cold (15 degrees C) 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. 5. With increasing incidence of bursts transient electrodermal or plethysmographic responses following individual bursts merged, and thus the fast neural rhythms were not discernible in either the electrodermal or Pleth traces. Given increments in firing rate of nerves produced less additional vasoconstriction at high than at low firing rates. The rhythm generating mechanisms may help to restrict rates of individual fibres to the low range which provides high gain in the neuroeffector transfer functions.
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