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Biomedical subjects

A Mannard

Publications and source records attributed to A Mannard.

9 recordsLinked to original sources
PubMed1977

Effect of post-impulse depression on background firing of sympathetic preganglionic neurons.

(1) Many of the preganglionic neurons responsible for sympathetic tone in the cat exhibit a characteristic irregular background spike activity with a low repetition rate. The properties of this activity, described by the interspike interval histogram, can be explained as the result of the responses of the neurons to random synaptic imputs. (2) Serial interspike interval correlation was used to show that additive post-impulse depression in preganglionic neurons does not enter into the timing of typical low-rate, irregular background firing. However, if cells are accelerated by anitdromic tetanization, a depressive recovery process accumulates to cause a prolonged silent period after driving of the cells has ceased. If cells are accelerated, by the action of their synaptic inputs, to rates higher than their usual basal rates, serial post-impulse depressions overlap, and summate to cause a temporal interaction between neighboring pulses which is observable by serial interval correlation. (3) By observing the effect of antidromic responses occurring at various intervals after a background spike, we showed that the time course of the summative part of post-impulse depression is shorter than the interspike intervals typically encountered in background firing. (4) At higher-than-basal levels of sympathetic activity, occurring spontaneously or during antidromic stimulation, successive post-impulse recovery periods overlap and sum to impart a negative correlation of serial interspike intervals. At the levels of sympathetic activity existing in waking animals, the damping effect of cumulative post-impulse depression is probably an important factor in stabilizing sympathetic tone.

Action Potentials↗
PubMed1975

Principles underlying new methods for chronic neural recording.

Chronic recording is possible from nerve fibers which have grown through holes in an insulating medium (regeneration electrodes) or which are enclosed by an insulating sheath (cuff electrodes). Use of three electrodes in a balanced configuration permits good rejection of electromyographic (EMG) signals and other sources of electrical interference (fluorescent lights, 60 Hz signals from the mains, etc.). Equations are derived and tested for predicting the amplitude and form of the signals expected for a given cuff length and diameter. These equations can be used to design electrode units optimally for a given application. Finally, the use of transformers permits the neural signals to be carefully matched to the recording apparatus and further optimizes the neural signal-to-noise and signal-to-EMG ratios. Use of these methods in several physiological and clinical applications, as well as potential abuses, are discussed.

Animals↗
PubMed1974

Regeneration electrode units: implants for recording from single peripheral nerve fibers in freely moving animals.

Implantable electrode assemblies that become penetrated by regenerating axons were used to record signals from single sensory and motor nerve fibers associated with leg movement in unrestrained amphibians (Xenopus laevis). Such neuroimplants may provide a means for establishing the roles of various muscle afferents and efferents in posture and locomotion, and have potential clinical applications.

Action Potentials↗
PubMed1973

Determination of the frequency response of isometric soleus muscle in the cat using random nerve stimulation.

1. The frequency response of isometric soleus muscle was determined efficiently by analysis of the unfused tension generated during short periods of random stimulation of the divided ventral roots, in anaesthetized cats.2. Despite the complexities of skeletal muscle, the frequency response of soleus, at moderate lengths and stimulation rates in the physiological range, is closely approximated by the frequency response function for a simple, linear, second-order system near critical damping.3. The soleus muscle shows a uniformly high sensitivity to fluctuations in nerve activity over a range of frequencies similar to the range of frequencies of muscular activity observable during behaviour. The nerve-muscle preparation appears to be well suited for smooth and steady motor activity, since it is much less responsive to the higher frequency components contained in individual action potentials or generated in tremor.4. The second-order parameters: low-frequency gain, natural frequency and damping ratio provide useful descriptions of the changes in the muscle's response caused by variations of muscle length, nerve stimulation rate or number of active motor units.5. A reduction in tension incurred, for example, during fatigue can be compensated to some extent either by a lengthening of the loaded muscle or through an increase in neural spike repetition rate. However, both mechanisms produce concomitant increases in the ;sluggishness' (increased damping and lower natural frequency) of the preparation. This sluggishness may arise out of limitations imposed by the mechanism for the re-uptake of calcium into the sarcotubular system.6. One naturally occurring method of increasing tension, by recruitment of more active motoneurones, seems to be desirable because tension can be augmented in this way without an increase in sluggishness. This is presumably because recruitment increases the muscle's response without affecting excitation-contraction coupling in fibres already active.

Animals↗