Conduction Velocities and Their Temperature Coefficients in Sensory Nerve Fibres of Cockroach Legs

Abstract

1. Conduction velocities of individual afferent nerve fibres from tactile spines and proprioceptive campaniform sensilla have been measured in situ over the temperature range 5-42° C., in leg preparations of the cockroach Periplaneta americana. 2. Conduction velocities at 20° C. (u20) averaged 3.3±1.4 m./sec., ranging from 1.6 to 11.0 m./sec. 3. Temperature coefficients, expressed as Q10 for the interval 20-30° C., averaged 1.7±0.24, ranging from 1.3 to 2.6. 4. The length of the propagated disturbance is about 2-3 mm., and is nearly temperature-independent. 5. Fibre diameters, estimated from conduction velocity, must be about 10 µ. 6. There is no correlation between conduction velocity and distance from the sensillum to the thoracic ganglion. Conduction delays in fibres conducting within one standard deviation of mean u20 range from about 2 to 15 msec., from the most proximal to the most distal tactile spines. 7. The effect of conduction delay on temporal and spatial sensory encoding is probably unimportant from a behavioural point of view. It contributes a factor of the form exp(-sd/u) to the sensory transfer function, and may be appreciable at upper physiological frequencies of impulse frequency modulation.