ABSTRACT
Electrophysiological techniques have been applied to monitoring sensory discharges from the first antennae of calanoid copepods. Extracellular nerve impulse traffic from both mechanoreceptors and putative chemoreceptors has been recorded. The first antennae of some, but not all, calanoid groups possess “giant” mechano receptive axons generating very large (mV) extracellular signals. There are two such giant antennal mechano receptors (GAMs) innervating setae of each distal tip. These are sensitive to small (< 10 nm) controlled hydrodynamic disturbances, including abrupt displacements and sinusoidal vibrations with frequencies up to and exceeding 2 kHz. Behavioral studies show that escape “jumps” can be triggered in Labidocera madurae by the same types of disturbances. Sensitivities as low as 4 nm were observed at frequencies of ca. 900 Hz. Behavioral sensitivities are similar to those measured physiologically and suggest that firing of the GAMs is capable of triggering escape behavior, perhaps even with a single nerve impulse.
