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J Storm

Publications and source records attributed to J Storm.

6 recordsLinked to original sources
PubMed1990

Computer-controlled wheelchair ergometer.

A new wheelchair ergometer has been designed in which a combination of realistic simulation of wheelchair propulsion--with adjustable parameters for rolling resistance, air drag, wind speed and slope--and force measurement has been realised. The static solution enables the measurement of physiological and kinesiological parameters. All data from force transducers in seat and backrest, torque transducers in the wheels and force transducers in the wheelframes as well as the acquired speed are sampled in a data-acquisition system. An offline curve processor allows the acquired data to be processed with standard or custom-programmed routines. Preliminary results have been added and are discussed.

Engineering↗
PubMed1987

Thresholds of action potentials evoked by synapses on the dendrites of pyramidal cells in the rat hippocampus in vitro.

1. In this study we have measured the thresholds of action potentials and some properties of e.p.s.p.s (excitatory post-synaptic potentials) produced by activation of distal and proximal dendritic synapses in CA1 pyramidal cells in rat hippocampal slices. 2. Simultaneous intracellular and extracellular electrophysiological recordings were made from pyramidal cells. The two recording electrodes were positioned very close together to provide an accurate measurement of the transmembrane potential by subtraction of the extracellular field from the intracellular potential. 3. Two pairs of stimulating electrodes were placed in the stratum radiatum of area CA1. The proximal and distal afferents were stimulated alternately within a 15 s cycle and at an intensity to produce action potentials in about 50% of the trials. 4. At this stimulus intensity there was a slight difference in the mean 10-90% rise times of the e.p.s.p.s produced by stimulation of proximal and distal afferents. The ratio of the distal: proximal rise time was 1.27. 5. In those trials where the action potential failed there was also a significant difference in the time-to-peak of the e.p.s.p.s evoked from proximal or distal sites. The times-to-peak of the e.p.s.p.s from proximal stimulation were between 1.5 and 3.8 ms, whilst the times-to-peak from distal stimulation were longer (2.1-7.2 ms). 6. In 16/18 cells included in this study the thresholds for action potentials evoked by distal stimulation were significantly lower than those following proximal activation. The mean threshold for distal activation was 12 mV compared with 16 mV for proximal activation. 7. The threshold of action potentials activated by depolarizing current pulses appeared to be close to that for action potentials evoked from proximal synapses. 8. Whilst the shape indices of the e.p.s.p.s were slightly different when comparing transmembrane with conventional intracellular recordings, the thresholds of the action potentials were not affected by this procedure. 9. Possible explanations for the low threshold for action potentials evoked from distal synapses are discussed, including an active dendritic membrane and differences in inhibition.

Action Potentials↗
PubMed1985

Repetitive firing of CA1 hippocampal pyramidal cells elicited by dendritic glutamate: slow prepotentials and burst-pause pattern.

In order to compare responses to dendritic vs. somatic depolarization, CA1 pyramidal cells in rat hippocampal slices were stimulated by iontophoresis of glutamate to sensitive spots in the dendrites, and by somatic current injection. Low intensities of either stimulus elicited slow repetitive firing. Each action potential was preceded by a slow depolarizing prepotential (SPP), lasting 50-300 ms and was followed by fast (3-5 ms) and slow (more than 100 ms) afterhyperpolarizations (AHPs). The SPPs, and AHPs were indistinguishable for the two types of stimuli. In response to strong depolarizations, most cells showed an initial burst of spikes, followed by a pause before the steady discharge. This pattern was elicited by both glutamate and current. The input resistance usually increased 5-20% during subthreshold depolarizations by glutamate or current. In contrast, large doses of glutamate caused a slow decline in the resistance (up to 40%), which was larger than during comparable current-induced discharge, and the response was followed by a longer AHP. It is concluded that both dendritic and somatic depolarization, induced by glutamate and current, respectively, can elicit sustained repetitive firing with SPPs, fast and slow AHPs and burst-pause pattern, thus, increasing the likelihood that these phenomena play a role during natural activation of CA1 cells.

Animals↗
PubMedDate not supplied

A new x-ray and light field superimposition detector.

A fast and accurate method to determine the alignment of the diagnostic x-ray and light fields was developed. Following the exposure, the boundaries of an x-ray field are determined by a custom-built x-ray field position detector and indicated by light-emitting diodes. The alignment of the supposed and the actual x-ray fields agree (within +/- 2 mm) with the corresponding results of the film-based procedure.

Humans↗