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Biomedical subjects

R M Jell

Publications and source records attributed to R M Jell.

At least 19 recordsLinked to original sources
PubMed1992

Stimulus velocity dependence of human vertical optokinetic nystagmus and afternystagmus.

Stimulus velocity dependence of human VOKN and VOKAN was investigated using 20 degrees, 40 degrees, 60 degrees, and 80 degrees/s optokinetic stimulation. In our experimental conditions, 40 degrees/s was found to be the most appropriate stimulus velocity for inducing reliable VOKN and VOKAN based on the analysis of SPV, gain, and the area under the VOKAN decay curve. There was a clear trend toward up/down asymmetry of VOKN gain, with higher upward OKN SPV than downward at 40 degrees/s. VOKAN with both short and long time constant components was induced in 5 of 11 subjects, but only when the stimulus was upgoing. Stimulation at 20 degrees/s in either direction produced a decay with only a short time constant. VOKN-SPV and the area under VOKAN decay curve at 40 degrees/s showed no significant difference from the corresponding values at 60 degrees/s or 80 degrees/s, indicating that following and the velocity storage mechanism had saturated at 40 degrees/s. However, the gain at 60 degrees/s and 80 degrees/s became low and eye movement regularity was poor. Stimulation at 20 degrees/s may activate mainly the vertical pursuit mechanism, as it did not produce up/down asymmetry. It is proposed that, as in the horizontal case, two kinds of mechanisms are involved in vertical stripe-following eye movements, which represent smooth pursuit and optokinetic systems respectively.

Adult↗
PubMed1988

Convergent effects from vestibulospinal tract and primary cutaneous afferent fibers on motoneurons to proximal lower limb flexor and extensor muscles in humans.

In human subjects, the latency and magnitude of cutaneomuscular test reflexes, evoked by stimulation of the sural nerve in the contralateral and ipsilateral quadricep and hamstring muscles, were investigated during static tilts in the pitch axis. The ANOVA demonstrated a highly significant, tilt-dependent modulation of the magnitude of the test reflex for the initial phase of both ipsilateral quadriceps and ipsilateral hamstrings. These results are consistent with results from a similar study on human ankle muscles and provide further evidence that the tilt-dependence of these cutaneomuscular reflexes originates from activity in the otolith receptors.

Afferent Pathways↗
PubMed1988

Concussion. Acceleration limits causing concussion.

Among the many features common to all species of the animal kingdom is the transient loss of function of the nervous system as the result of a jarring blow, a phenomenon known as concussion. Understanding of concussion has been hampered by the lack of a uniform definition, with many authors including cases with gross, irreversible changes. The phenomenon occurs only with a blow that significantly accelerates and thus is best defined as "a transient disturbance of neuronal function as a result of acceleration." There must be a threshold beneath which no loss of function occurs and a ceiling beyond which changes are not reversible. Experiments with nonanesthetized frogs revealed that at 33 g only the occasional frog would be stunned. From 50 to 230 g, consciousness was always lost but rapidly regained and retained, while beyond, the loss was not always reversible. The time of functional loss was increasingly proportional to acceleration.

Acceleration↗
PubMed1988

Effect of active head movements about the pitch, roll, and yaw axes on human optokinetic afternystagmus.

Effects of active head movements about the pitch, roll, or yaw axes on horizontal optokinetic afternystagmas (OKAN) were examined in 16 subjects to test the hypothesis that otolith organ mediated activity induced by a change in head position can couple to the horizontal velocity storage in humans. Active head movements about the pitch axis, forwards or backwards, produced significant OKAN suppression. Pitch forward head movements exerted the strongest effect. Active head movements about the roll axis towards the right also produced OKAN suppression but only if the tilted position was sustained. No suppression was observed following sustained yaw. However, an unsustained yaw left movement after rightward drum rotation significantly enhanced OKAN. Sustained head movement trials did not significantly alter subsequent control trials. In contrast, unsustained movements about the pitch axis, which involve more complex interactions, exerted long-term effects on subsequent control trials. We conclude that otolith organ mediated activity arising from pitch or roll head movements couples to the horizontal velocity storage in humans, thereby suppressing ongoing OKAN. Activity arising from the horizontal canals during an unsustained yaw movement (observed mainly with yaw left), following drum rotation in a direction contralateral to the movement, may also couple to the velocity storage, resulting in increased activity instead of suppression.

Adolescent↗
PubMed1988

The influence of active versus passive head oscillation, and mental set on the human vestibulo-ocular reflex.

We compared passive (manual) whole body, and active head oscillation in normal human subjects attempting mentally to influence the vestibulo-ocular reflex (VOR). Our objective was to establish simple procedural guidelines for vestibular test procedures in clinical settings. Using a head-fixed target, both methods of oscillation yielded virtually zero gain. Using an Earth-fixed target, active oscillation gain was unity, while passive gain was slightly less than 1. Using an imagined Earth-fixed target in the dark, both active and passive gains were reduced considerably, but passive gain was reduced more. Using an imagined head-fixed target in the dark, VOR gain was near zero at low frequencies but increased as frequency increased. Again, passive gain was less than active gain. At frequencies above 1 Hz, VOR gain in all conditions approached a value between 0.7 and 0.9. We conclude that active and manual passive rotation are simple and effective methods to test the VOR, but emphasize that visual and mental influences must be carefully controlled.

Adult↗
PubMed1987

Convergent effects from vestibulospinal tract and primary cutaneous afferent fibers on motoneurons to ankle extensor and flexor muscles in humans.

The latency and magnitude of cutaneomuscular reflexes, evoked by stimulation of the sural nerve in the contralateral and ipsilateral tibialis anterior and soleus, were investigated in normal human subjects during static tilts in the pitch axis. For all subjects the test reflex consisted of oscillating sequences of excitation and inhibition, each muscle exhibiting a characteristic pattern defined by its latency and sign of the initial phase. The latency of the various components and the sign of the initial phase did not vary with angle of tilt. However, the results of an ANOVA demonstrate a highly significant tilt-dependent modulation of the amplitude of the test reflex for the initial inhibitory phase of the contralateral tibialis anterior. We propose that this tilt-dependent effect on the crossed cutaneomuscular reflex originates from activity in the otolith organ receptors.

Adult↗
PubMed1985

Initiation of locomotion from the mesencephalic locomotor region: effects of selective brainstem lesions.

The effects of selected brainstem lesions on controlled treadmill locomotion produced by stimulation of the mesencephalic locomotor region (MLR) in postmamillary cats were determined in these experiments. The importance for the initiation of locomotion of projections from the MLR to rostral brainstem structures, described in a preceding paper, were examined by selective lesioning or by adjusting the level of the decerebration. The role played by the lateral vestibulospinal tract (LVST) in the initiation of locomotion was examined by lesioning Deiters' nucleus bilaterally. Contrary to previous claims, the results of the present experiments show that areas of the brainstem rostral to the MLR are not required for the initiation of locomotion by MLR stimulation. This finding eliminates the ventral tegmental area of Tsai and the substantia nigra, both implicated in the initiation of locomotion, as required participants in MLR stimulated locomotion. Bilateral Deiters' nucleus (DN) lesions did not significantly affect the initiation of locomotion from the MLR, nor did such lesions alter in a systematic fashion the amplitude or timing of EMG activity in flexor or extensor muscles of the hindlimb during MLR evoked walking. Joint angle changes during the locomotor cycle were also essentially unaltered by DN lesions. The significance of these findings regarding the brainstem structures which must be involved in the initiation of locomotion are discussed.

Animals↗
PubMed1979

Visual-vestibular interactions: I. Influence of peripheral vision on suppression of the vestibulo-ocular reflex and visual acuity.

Legibility of head-fixed displays in some motion environments is partially dependent upon visual suppression of the vestibuloocular reflex (VOR). This study investigates the effects of differing relationships between peripheral background movement and whole-body motion on the VOR and on visual performance. The purpose of the study is to explore factors in motion environments that influence performance limits and to develop procedures of potential usefulness in evaluating interacting visual and vestibular function. Visual performance and visual suppression of the VOR were markedly different, depending upon the relative direction of peripheral background movement. Visual suppression of the VOR, and visual performance, were disrupted far more when vestibular inputs and peripheral optokinetic inputs were discordant than when they were concordant. Results have potential implications for head-up displays and suggest a procedure for evaluating visual/vestibular function.

Acceleration↗
PubMed1976

Action of prostaglandin synthetase inhibitors on rostral hypothalamic neurones: thermoregulation and biogenic amines.

Sensitivity of neurones in the rostral hypothalamus of methoxyflurane anesthetized cats to the prostaglandin synthetase inhibitors (PGSIs), salicylate and fenoprofen, has been examined using the technique of microiontophoresis. Results were compared with sensitivity to prostaglandin (PG) E1 and no noradrenaline (NA) and 5-hydroxytryptamine (5HT). Simultaneous applications of PGSIs and NA or 5HT were made to investigate the role of PG in monoamine induced changes in neuronal excitability. PGSIs did not excite these cells, but depression were common, particularly with fenoprofen. PGE1 did not reverse the depressions. NA and 5HT responses were generally unaffected by simultaneous PGSI application and responsiveness to PGSIs was found to be unrelated to amine sensitivity. The results support the conclusion that PGSIs have a depressant action on neurones in this region, which may not be related to inhibition of prostagladin synthesis, and that the actions of microiontophoretically applied NA and 5HT are not dependent upon PG.

Action Potentials↗
PubMed1974

Responses of rostral hypothalamic neurones to peripheral temperature and to amines.

1. Five-barrelled micropipettes have been used to record extracellularly the activity of neurones in the rostro-medial hypothalamus of methoxyflurane-anaesthetized cats, and to apply acetylcholine (ACh), noradrenaline (NA) and 5-hydroxytryptamine (5-HT) by micro-iontophoresis to the vicinity of each neurone encountered. Peripheral thermal stimulation was achieved by blowing warm (42 degrees C) and cold (4 degrees C) air in the face of the animal, and thermoresponsiveness was compared with amine responsiveness.2. One hundred and twenty-two neurones were obtained from ten cats. Eleven (9%) were warm-responsive and sixteen (13%) were cold-responsive. The rest did not respond to facial warming or cooling.3. No consistent relationship was observed between amine responses and responsiveness to facial temperature. Warm-responsive neurones were mainly depressed or unaffected by amines. Cool-responsive neurones were excited, depressed or unaffected by amines with the exception that no 5-HT excitations were seen. Thermoresponsive neurones were more likely to be amine depressed than non-thermoresponsive neurones.4. Six thermoresponsive neurones responded to peripheral temperature and to amines in a way which fitted the amine model of Myers (1971). Fifteen thermoresponsive neurones fitted the model of Bligh, Cottle & Maskrey (1971), according to the same criteria.5. The results lend little support to the amine model, as predicted from amine micro-injection and release studies in primates, but support more strongly the model of Bligh et al. (1971) which is based on intraventricular injections of amines in sheep, goats and rabbits. On the basis of the latter model, functional identification was possible in 63% of the thermoresponsive rostral hypothalamic neurones tested.

Acetylcholine↗
PubMedDate not supplied

Human optokinetic afternystagmus. Effects of repeated stimulation.

Normal human subjects were exposed to repeated optokinetic afternystagmus (OKAN) testing in either one direction or alternating directions of stripe movement. Sessions were conducted at intervals of either one week or several weeks. Repeated exposure to OKAN stimulation in one direction produced significant response decrements in cumulative displacement, short time constant, long time constant, and the coefficient of the long time constant component (C). The data suggest that the decrease in C and cumulative displacement occurred most noticeably between trials 3 and 4 of the first session. Retesting after 1 week, and up to 8 weeks later revealed no recovery. Repeated exposure to alternating leftward and rightward stimuli resulted in response decrement in both cumulative displacement and C. Responses to leftward stimuli were indistinguishable from responses to rightward stimuli.

Adult↗
PubMedDate not supplied

Human optokinetic afternystagmus. Charging characteristics and stimulus exposure time dependence in the two-component model.

The dependence of human optokinetic afternystagmus (OKAN) velocity storage (charging) and optokinetic nystagmus (OKN) characteristics on optokinetic (OK) stimulus exposure time was investigated, using the two-component double exponential model for OKAN decay. Results are compatible with our previously proposed concept of two velocity storage integrators, one responsible for the short time constant decay (pursuit-mediated) and the other for the long time constant decay (OK system-mediated). The dependence of the long time constant integrator of OKAN on stimulus exposure time was clearly demonstrated. The short time constant integrator appeared to be independent of stimulus exposure time within the range studied. We conclude that the charging time-course of each component is distinct from that of the other. The time constants of each component decay were found to be invariant. A left-right asymmetry observed in both OKN and OKAN responses suggests that the integrators are direction sensitive.

Adult↗