Timing Of Impulses Research Articles

TVR and vibration-induced timing of motor impulses in the human jaw elevator muscles.

In order to investigate myotatic reflex involvement in jaw muscle control, an analysis was made of the motor responses induced by mechanical vibration (120-160 Hz) of the jaw elevator muscles in healthy subjects. As seen in torque measurements and mean-voltage electromyographic (EMG) recordings, the vibration caused involuntary reciprocal changes in jaw muscle tone, the contraction force increasing in jaw elevators and decreasing in antagonistic jaw opening muscles. This tonic vibration reflex (TVR) elicited from the jaw elevators exhibited many characteristics similar to those previously described for limb muscle tonic vibration reflexes: it varied in strength from one subject to the next independently of the briskness of the jaw elevator tendon jerks; it had a gradual onset with successive recruitment of jaw elevator motor units firing largely out of phase with one another and at rates much lower than the vibration frequency; it was susceptible to voluntary control--when allowed visual feed-back from the torque meter all subjects were able to suppress the TVR and keep mean contraction force constant. The results indicate that with respect to the tonic motor response to sustained inflow in the Ia afferent nerve fibres, the jaw elevators do not differ markedly from other skeletal muscles. Independently of whether a TVR was present or not, the vibration caused a timing of the motor unit discharges in the jaw elevators that could not be controlled voluntarily and that showed up in gross EMG recordings as a marked grouping of discharges synchronous with each wave of vibration. A similar but less distinct grouping of the gross EMG pattern was seen in limb muscles exposed to vibration, the dispersion increasing with the peripheral conduction distances of the reflex arcs. It is suggested that contrary to the TVR, which depends on the sustained mean level of the Ia afferent input, the timing phenomenon depends, like the tendon jerk, on the degree of synchrony in the afferent Ia volleys. Monosynaptic projections may well be involved in the dynamic timing of motor discharges during tonic firing, but this does not imply that the TVR or the tonic stretch reflex is dependent upon such projections.

Minicomputer identification and timing of nerve impulses mixed in a single recording channel

The use of a minicomputer on-line to identify and measure the time series of different nerve impulses mixed in a single recording channel is described. The study involves electrical discharges recorded simultaneously from two of the olfactory receptors found on the antenna of the male red-banded leaf roller moth. These receptor cells were stimulated by odors normally secreted by the female which have been shown to act as powerful sex attractants to the male. The computer program stores the time interval between nerve spikes and 30 100-µs samples of the waveform of each spike detected. An ensemble of up to 1000 sets of samples can be stored in the course of an experiment on a 32K-word magnetic disk, through a data channel facility. A statistic is calculated on the sampled data for each spike in the ensemble. The range in values of this statistic is used to characterize the data by plotting a histogram of the nerve-spike parameter. This display can then be partitioned so as to identify the two units of interest. On the basis of this identification, a distinct time series for each receptor is computed and filed on the minitape for further data analysis.

Analytical guidance in the neighborhood of optimal multi-impulse trajectories

A first-order minimum propellant guidance law is developed for multi-impulse trajectories in an inverse-square gravitational field. A second-order variational analysis is used to formulate the guidance problem as an accessory minimum problem, i.e. minimize a quadratic form (second-variation in propellant consumption) subject to linear constraints (variational equations of motion and deterministic boundary conditions). Solution of the accessory minimum problem provides the optimal guidance law in feedback form. It is emphasized that this analysis takes into account the nominal impulse programme when calculating the optimal guidance corrections. It is shown that for multi-impulse transfers it is in general, non-optimal to add impulses. All corrections to the trajectory should be made by a combination of small changes in timing, magnitude and direction of the nominal impulses.

Relationship of surface electrogram recordings to activity in the underlying specialized conducting tissue.

Surface electrodes are widely used to study the electrophysiology of the A-V conducting system. The recording of activity from the human in-situ His bundle represents a practical, clinically useful adaptation of surface recording technics. The interpretation of data accumulated by this means must be considered in relation to the extent to which the surface recordings from the specialized conducting system accurately reflect activity in the underlying tissue. A combination of microelectrode technics to record transmembrane action potentials and surface recording technics on isolated preparations of canine conducting tissue were used to approach this question. Under many conditions the surface electrogram was found to be an accurate indicator of the presence and timing of impulses in the conducting system. However, during early premature activity, marked decreases or complete absence of surface electrogram voltage could occur at coupling intervals at which premature impulses were still able to propagate through tissue under the electrodes. In addition, early premature activity could be associated with reversal of polarity of the surface electrogram without reversal of the direction of propagation. Inaccurate relationships between the time of inscription of the surface recording and the time of passage of the propagating wavefront beneath the surface electrodes also occurred with early premature impulses. Finally, there is some evidence that surface electrograms primarily reflect that activity in the most superficial levels of tissue.

Electrical thresholds of unimpaled corticospinal cells in the cat.

Previous measurements of cortical electrical thresholds for firing impaled pyramidal cells in the cat have now been checked on unimpaled cells, whose discharges were led from their axons in cervical spinal white matter. The thresholds are higher than those for impaled cells, but are still below the threshold for movement. Long pulses evoked repetitive discharges. Currents causing movement caused firing of cells whose lowest‐threshold foci were as far as 7 mm. distant from the lowest‐threshold motor “point”. Currents of intermediate strengths evoked synaptic potentials in spinal motoneurones. Thresholds and timing of pyramidal impulses and of synaptic potentials afford no evidence of monosynaptic connexion between pyramidal axons and motoneurones, such as occurs in primates.