Mechanoreceptors for near-field water displacements in crayfish

Abstract

1. Mechanosensory hairs on the surface of the crayfish telson are dually innervated, one sensory cell responding to headward, the other to tailward deflection of the hair. The average conduction velocity of headward elements was 0.8 m/s (variance 0.08) and of tailward elements 1.2 m/s (variance 0.19). In a frequency range from 0.05 to 200 Hz, thresholds were lowest near 20 Hz: 0.08 mum (pp) for headward-sensitive and 0.1 mum (pp) for tailward-sensitive cells. 2. The receptors are displacement sensitive since thresholds are of the same order of magnitude over the frequency range 1-70 Hz when the hair is moved by a vibrating wire loop. With natural stimuli (surface waves), the velocity component of the particle movement (and consequently force) becomes influential. The coding of a broad range of stimulus intensities is aided by variations in mechanical properties of the hair. 3. Marked directionality (better than 4:1), in addition to the dual innervation, enhances vector detection. At least part of this characteristic stems from the hingelike articulation of the hair on the body surface: the hair can be moved easily 40 degrees tailward and 20 degrees headward, but must be forced in the orthogonal direction. Morphological studies indicate the presence of a double pivoted hinge, with rigid guides for movement of the hair shaft. Preliminary results of electron microscope examination show a clearly polarized arrangement of densely packed microtubules in the two dendrites; they appear interconnected in groups of two and three along a line parallel to the sensitivity plane of the receptor. 4. The 50-fold threshold difference between the results of behavioral experiments in lobsters (24) and the data for the individual receptors reported here may be due to improvement in signal-to-noise ratio by central nervous averaging of the input from an estimated 2 X 10(3) receptors (Procambarus), and/or to the kind of threshold criteria applied to individual receptor thresholds. As would be expected (35), the sensory cells of each directional class synapse with separate interneurons: in this way, the organism might employ differential microphones to reduce background noise. 5. The receptors are analogous to those of the lateral-line system in lower vertebrates in having receptors with sensitivities polarized by 180 degrees. These similarities suggest that in both cases monitoring of near field water displacements has proved in essential way of orienting in opaque waters.

A mechanism for neuronal coincidence revealed in the crayfish antennule

“…Data from 18 neurons have shown that at 10 Hz their mean threshold to sinusoidal oscillations of the fluid surface above the associated sensillum was 0.02 m (SD ϭ Ϯ0.009). Moreover, as do those displacements associated with the tailfan feathered sensilla (18), displacements of increasing velocity generate monotonic increases in mean impulse frequency up to saturation near 1,000 m/sec (Fig. 1F).…”

“…1C). Like feathered sensilla described on the tailfan (18) and earlier on the cephalothorax (20), each antennular sensillum is supplied by two sensory neurons that have opposite directional preferences in their respective sensitivity to displacements. Typical electrophysiological recordings from two standing feathered sensilla are shown in Fig.…”

“…Feathered sensilla are prominent near-field hydrodynamic sensors on the crayfish abdomen (18,19) and undoubtedly largely comprise the afferent limb of the lateral giant startle reflex. Morphologically similar standing feathered sensilla occur sparsely distributed along the ventro-lateral aspects of the lateral antennular flagellum and the ventro-medial aspects of the medial flagellum (Fig.…”

Animal perception in gravel-bed rivers: scales of sensing and environmental controls on sensory information

“…For example, a neural response was found when the sensory hairs on crustaceans were stimulated by flows as slow as 0.006 cm s -1 (Wiese 1976;Bleckmann 1994).…”

“…For example, the sensory hairs of crustaceans can number many thousands and are distributed across the whole body-length. The velocity threshold of hairs may be as low as 0.006 cm s -1 with each hair sampling at a rate of up to 150 Hz (Wiese 1976;Breithaupt and Tautz 1990). Therefore, crustaceans such as crayfish in rivers, may be able to gain detailed information about the turbulent characteristics of flow, and process substantially more than depth-and reach-averaged velocity information.…”