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101.
Shoichi Minota 《Pflügers Archiv : European journal of physiology》1995,429(4):570-577
The onset and time course of the muscarinic currents induced by brief applications of acetylcholine (ACh) were examined in voltage-clamped neurons of bullfrog sympathetic ganglia bathed in a solution containing d-tubocurarine. At a potential of –40 mV, the ACh-induced current (I
ACh) appeared within 1.2 s and rapidly increased to its peak with a half-activation time of 2.2 s. This initial current was termed the fastI
ACh and was blocked by 4 mM Ba2+. At a potential more negative than –60 mV, the fastI
ACh disappeared and the remainingI
ACh activated with a delay of 3.9 s and slowly increased to its peak with a half-activation time of 8.2 s. This delayed current was termed the slowI
ACh and is thought to be associated with inhibition of a K+ current, orI
M, as well as activation of an inward current through non-M-type muscarinic cation channels. The slowI
ACh was not inhibited by Ba2+, but its amplitude was reduced with depolarization (the extra-polated reversal potential was +3 mV). In Na+-free solution, the amplitude of the slowI
ACh reduced, but its polarity did not reverse in the voltage region examined (-30 to –100 mV). The slow excitatory postsynaptic current was also recorded, and was shown to have a similar delay in onset and slow time course. The results demonstrate that ACh activates the non-M-type muscarinic current three times more slowly than it inhibitsI
M. 相似文献
102.
A wireless power transfer system for endoscopic micro-robot operating at 36 kHz is presented in this paper. The issue of patient' s health and safety regarding exposure to the electromagnetic field is addressed. The specific absorption rate and current density can be used to investigate the electromagnetic influences on the biological tissues surrounded by the wireless power launching coil. In view of this purpose, the limited close-ound solenoid electromagnetic model is built, the relationship between the electric intensity and the specific absorption rate and current density is deduced, and the simulation experiments are done. Experimental results show that the values of SAR and current density related to different tissue catalogs are all very small and do not exceed their own limits respectively when the resonance frequency of operation is 36 kHz. 相似文献
103.
Effects of the presentation of false heart-rate feedback on the performance of two common heartbeat-detection tasks. 总被引:3,自引:0,他引:3
Research has indicated that performance on heartbeat counting tasks may be influenced by beliefs about heart rate. Sixty male subjects were administered the Schandry heartbeat counting task after viewing fast, slow, or no heart rate feedback. Subjects were also administered the Whitehead signal-detection type task. Results indicated that subjects who received fast or no heartbeat feedback performed better on the Schandry task than subjects who received slow feedback. Feedback presentation did not affect performance on the Whitehead task. These results suggest that the Schandry task is influenced by external variables (expectations, beliefs) beyond pure awareness of "discrete" visceral sensations and, thus, may not be as powerful a method for determining awareness of individual heartbeats as some other paradigms. 相似文献
104.
L. E. Sergio Stephen H. Scott 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1998,122(2):157-164
This study examines whether the kinematics of pointing movements are altered by the sensory systems used to select spatial
targets and to guide movement. Hand and joint paths of visually guided reaching movements of human subjects were compared
with two non-visual conditions where only proprioception was available: (1) movements of the same subjects with blindfolds,
and (2) movements by congenitally blind subjects. While hand-path curvatures were overall quite small, sighted subjects wearing
a blindfold showed a statistical increase in hand-path curvature compared with their visually guided movements. Blindfolded
subjects also showed greater hand-path curvature than blind subjects. These increases in hand-path curvature for blindfolded
subjects did not always lead to a decrease in joint-path curvature. While there were differences between blind subjects and
sighted subjects using vision for some movement directions, there was no systematic difference between these two groups. The
magnitude of joint-path curvature showed much greater variation than hand-path curvature across the movement directions. We
found variation in joint-path curvature to be correlated to two factors, one spatial and one geometrical. For all subject
groups, joint-path curvature tended to be smaller for sagittal-plane movements than for transverse or diagonal movements.
As well, we found that the magnitude of joint-path curvature was also related to the relative motion at each joint. Joint-path
curvature tended to increase when movements predominantly involved changes in shoulder angle and was minimal when movements
predominantly involved elbow motion. The consistently small curvatures of hand trajectory across blind and sighted subjects
emphasize the powerful tendency of the motor system to generate goal-directed reaching movements with relatively straight
hand trajectories, even when deprived of visual feedback from very early in life.
Received: 16 July 1997 / Accepted: 20 May 1998 相似文献
105.
M. V. Thomas 《Medical & biological engineering & computing》1977,15(4):450-454
A circuit is described which allows the input capacitance of an f.e.t. input integrated circuit to be used both as the feedback capacitance to neutralise the total input capacitance and to inject current pulses into the input. Compared with the conventional method of adding discrete capacitors to perform these functions, this design results in a lower total capacitance at the input, which reduces the high-frequency noise generated by the amplifier and facilitates the achievement of a low effective capacitance. A modified version having an ultralow (0·1pA) input current, for use with ion-sensitive microelectrodes, is also described. 相似文献
106.
The aminoglycoside antibiotic, gentamicin (GM), depressed the plateau phase and shortened the duration of the action potential in guinea pig papillary muscle. Its effect on the membrane currents was studied by a single sucrose gap voltage clamp method. The slow inward current (is) was remarkably diminished by GM with little change in its time course, in the voltage-dependency of the steady-state inactivation and activation or in its reversal potential. The maximal amplitude of is, obtained by subtracting the Co2+-resistant current, was reduced to 57% by 0.1 mmol/l GM and almost reduced to zero by 1 mmol/l GM. The efficacy of GM in inhibiting is was reduced by increasing the external Ca2+ concentration from 1.8 to 5.4 or 10.8 mmol/l, but not by the application of adrenaline. The time-dependent outward current (iK) was also decreased by GM but only at higher concentrations. It is proposed that the depressant action of GM on is was due to a blockade of slow channels, whereby GM may have dislocated Ca from the binding sites at slow channels on the external surface of the membrane. 相似文献
107.
Grande G Cafarelli E 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2003,150(4):449-457
Vibration of the patellar tendon recruits motor units in the knee extensors via excitation of muscle spindles and subsequent
Ia afferent input to the α-motoneuron pool. Our first purpose was to determine if the recruitment threshold and firing rate
of the same motor unit differed when recruited involuntarily via reflex or voluntarily via descending spinal pathways. Although
Ia input is excitatory to the α-motoneuron pool, it has also been shown paradoxically to inhibit itself. Our second purpose
was to determine if vibration of the patellar tendon during a voluntary knee extension causes a change in the firing rate
of already recruited motor units. In the first protocol, 10 subjects voluntarily reproduced the same isometric force profile
of the knee extensors that was elicited by vibration of the patellar tendon. Single motor unit recordings from the vastus
lateralis (VL) were obtained with tungsten microelectrodes and unitary behaviour was examined during both reflex and voluntary
knee extensions. Recordings from 135 single motor units showed that both recruitment thresholds and firing rates were lower
during reflex contractions. In the second protocol, 7 subjects maintained a voluntary knee extension at 30 N for approximately
40–45 s. Three bursts of patellar tendon vibration were superimposed at regular intervals throughout the contraction and changes
in the firing rate of already recruited motor units were examined. A total of 35 motor units were recorded and each burst
of superimposed vibration caused a momentary reduction in the firing rates and recruitment of additional units. Our data provide
evidence that Ia input modulates the recruitment thresholds and firing rates of motor units providing more flexibility within
the neuromuscular system to grade force at low levels of force production.
Electronic Publication 相似文献
108.
F. Richer M. Martinez H. Cohen J. -M. Saint-Hilaire 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1991,87(3):649-652
Summary Visual phenomena evoked by direct electrical stimulation of extrastriate cortex were observed in 30 epileptic patients as part of a presurgical investigation. An incremental sequence of low-level bipolar stimulation trains was delivered at medial and lateral pairs of contacts of stereotaxically-implanted multilead intracerebral electrodes in parietal, occipital and posterior temporal regions. Diffusion of stimulus afterdischarges was monitored by electrodes in temporal and frontal lobes and by the non-stimulated contacts of the stimulated electrode. Localized stimulations evoked few visual phenomena. The strongest anatomo-perceptual correlation was found for stimulation in the medial parieto-occipital fissure which evoked visual motion phenomena in all three patients stimulated in that region. The evoked motion perceptions were not associated with eye movements or any particular localization of the epileptic focus. These perceptions were only evoked once outside of the medial PO region at the 61 sites examined. The results suggest that the medial parieto-occipital region is closely linked to the human visual motion processing system. 相似文献
109.
Slow outward currents were recorded from voltage-clamped neurones in nodose ganglia excised from rabbits. In the majority of Type C neurones, a short depolarizing command pulse evoked a slow outward tail current (I
SAH) with a decay time constant ranging from 0.5 to 2 s. TheI
SAH was due to an increase in membrane conductance to K+ because its reversal potential was approximately equal to the Nernst potential for K+. TheI
SAH was reversibly blocked by removal of external Ca2+ or by Ca2+ antagonists. A Ca2+ ionophore, A23187, produced an outward current which was similar to theI
SAH. TheI
SAH was resistant to tetraethylammonium and depressed by Ba2+, whereas it was not affected by Cs+ and 4-aminopyridine. TheI
SAH was initially augmented and subsequently depressed by apamin (1–10 nM) and (+)-tubocurarine (100–600 M). It is concluded that theI
SAH in visceral primary neurones may be due to a long-lasting increase in K+ conductance caused by an increase in the concentration of intracellular Ca2+, resulting from Ca2+ entry during the depolarizing command pulse. 相似文献
110.
Role of actin microfilament in osmotic stretch-induced increase of voltage-operated calcium channel current in guinea-pig gastric myocytes 总被引:5,自引:0,他引:5
Wen Xie Xu Sung Joon Kim Insuk So K. W. Kim 《Pflügers Archiv : European journal of physiology》1997,434(4):502-504
Using the whole-cell patch clamp technique, the role of actin microfilament in hyposmotic increase of voltage-operated calcium
channel current (I
Ba) was studied in guinea-pig gastric myocytes. Hyposmotic superfusate (212 mOsm) increased peak I
Ba amplitude by 32.7 ± 6.5%; when cytochalasin-D (Cyt-D, 20 μM), an actin cytoskeleton disruptor, was used, an increase of only
9.7 ± 3.1% was seen. I
Baresponse to osmotic stress was potentiated (45.1 ± 4.1% increase) by 20 μM phalloidin, an actin microfilament stabilizer.
However, colchicine (100 μM), an microtubule cytoskeleton disruptor, had no effect on either I
Ba or its response to hyposmotic solution. Phalloidin also induced a rightward shift of the I/V relationship of I
Ba, while Cyt-D itself had no effect. These results suggest that actin cytoskeleton may mediate hyposmotic stretch-induced I
Ba increase in gastric smooth muscle.
Received: 26 March 1997 / Received after revision: 28 May 1997 / Accepted: 3 June 1997 相似文献