A Review of Recent Developments in The Study of Electroreception in The Platypus.

Abstract

This is a review of the current state of knowledge of the electrosensory system in the platypus. The structures in the platypus bill which generate the electroreceptor activity are the mucous sensory glands. The receptors respond to both DC and AC signals, negativity at the mouth of the gland exciting the receptor, positivity silencing it. Maximal sensitivity to AC signals is in the 50Hz - 100Hz range. The function of the serous sensory gland, also found in skin of the bill, remains unknown. The afferent nerve fibres are part of the trigeminal system and project to the cerebral cortex on the contralateral side. Cortical cells responsive to mechanical stimuli are found adjacent to cells responsive to both mechanical and electrical stimuli. Behavioural experiments show that the sensitivity to electrical stimuli is greatest for voltage sources at right angles to the bill's long axis. It is proposed that the platypus' ability to detect DC fields is important for the detection of steady bioelectric potentials generated by prey items and for the orientation around obstacles which generate contact potentials. The AC sensitivity is more likely to be concerned with detection of electromyogenic signals generated by moving prey.