Effects of nerve impulses on threshold of frog sciatic nerve fibres.

Abstract

SUMMARY1. The firing thresholds of single myelinated fibres of frog sciatic nerves were monitored as a function of impulse activity in the fibre. The threshold was given by the number of coulombs in current pulses that excited a particular fibre half the time when delivered to the whole nerve. Threshold was tracked by a device that incrementally decreased the number of coulombs in the current pulse whenever the fibre responded and increased the pulse if it did not respond.2. There was a pattern to the after-oscillations of threshold following activity. The fibres were briefly refractory, transiently superexcitable for about 1-1-5 sec and then entered a phase of raised threshold or 'depression' that lasted for many minutes.3. Activity produced little change in the threshold curve during the refractory period. Strong depressions following prolonged activity prevented the threshold from returning to the base-line level within the time associated with the refractory period for the same fibre at rest.4. After an impulse, superexcitability reached a maximum within 7-20 msec. This peak was larger as the number of impulses in a preceding burst increased and as the intervals between the impulses became briefer. Each successive impulse of a burst contributed less to the growth of superexcitability, and after the burst had 6-10 impulses additional impulses contributed nothing.5. The depression phase was marked by the interaction between build-up, which depended on the activity rate, and recovery, which required as long as an hour or more for the threshold to be completely restored to resting level. These two mechanisms, one causing build-up and the other recovery, led to formation of dynamic equilibria. The threshold level at equilibrium increased monotonically with the activity rate.6. The processes associated with superexcitability interact with those producing depression. In active fibres showing raised thresholds, impulses are followed by a relative superexcitability that persists for at least as long as an absolute superexcitability (with threshold below the resting level) can be measured in the same fibre at rest.7. The duration of the superexcitable phase interpreted as a relative change in excitability was roughly the same regardless of the level of depression.8. The magnitude of the oscillation in threshold was five to ten times larger than the grey region (the range of stimuli for which response is probabilistic). It is 0022-3751/79/3290-0523 $01.50

Sensory afferents regenerated into dorsal columns after spinal cord injury remain in a chronic pathophysiological state

“…With repetitive stimuli, intact sensory axons show a progressive increase in action potential conduction latency (Raymond 1979;George et al 1984;Carley and Raymond, 1987;Shin et al 1997). To test whether regenerated axons also exhibit increased conduction latency, we compared the latency of the 1 st and the 5 th response in a train of stimuli.…”

Flexible Fiber Nanogenerator with 209 V Output Voltage Directly Powers a Light-Emitting Diode

“…When the input voltage is beyond the threshold voltage of the resting potential, a contraction of muscle would be induced by opening the valve of the action potential. 17 For a frog's sciatic nerve, the cells' resting potential ranges from −60 to −80 mV, and a voltage input of at least 50 mV at 1 Hz is necessary for innervation of the sciatic nerve.…”

Comparison of the after‐effects of impulse conduction on threshold at nodes of Ranvier along single frog sciatic axons.

“…One set, used for conditioning stimuli, was located upstream from the set of test electrodes used to measure the threshold. The use of a separate pair of electrodes for conditioning ensured that any changes in the current distribution at the electrode caused by passing the conditioning stimuli did not disturb the threshold measurement (Raymond, 1979;Carley, 1984). The stimulating cathode was normally at least 2 cm from the cut end of the nerve, when the stimulating electrode was closer than 1 cm to the cut end, the after-effects of activity were attenuated, and in some cases the depression phase was even inverted.…”

“…A given node generates currents which conduct through passive internodal regions to trigger action potentials at the next node (Huxley & Stiimpfli, 1949;Tasaki, 1953). Measurements of firing threshold in single axons from human median nerve (Bergmans, 1968a, c) and frog sciatic nerve (Raymond, 1979) have revealed that impulse activity in a fibre is followed by a characteristic sequence of oscillatory transients in the firing threshold. In frog axons each conducted impulse is followed by a brief (< 7 ms) refractory period during which the firing threshold is elevated.…”