Studies on the integration of sensory information by the nervous system of the brittlestarOphiura Ophiura

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Abstract
Multiple extra‐cellular recording electrodes were used to study information transfer within the nervous system of the brittlestar Ophiura ophiura subsequent to sensory stimulation. Experiments were carried out on minimally dissected whole animals or single arms and photic, mechanical and chemical stimuli were applied in a controlled fashion. Stimuli of all modalities that were above a threshold that could be considered threatening gave rise to activity conducted rapidly (80 cm/sec) and relatively unchanged throughout all radial nerve cords and the circumoral nerve ring. This activity does not produce motor output within the muscular effector systems but appears to produce a state of alert within the animal. Lower levels of stimulation produce activity that is conducted more slowly at about 35 cms/sec and in a decremental fashion. All motor output, whether it is associated with feeding or escape, is driven by this slower conducted activity. There is habituation to repeated stimuli but the timecourse varies with the particular sensory modality. If the rapidly conducting system shows habituation to one modality of stimulation and a second is subsequently applied, the response is normal even though the same interneurones are involved. There is facilitation of response when stimuli are applied close together. This study has shown that the notorious inconsistency of behavioural responses to similar stimuli, characteristic of this phylum, occurs at the final level of integration within the segmental ganglia of the radial cord that is presynaptic to the hyponeural motor neurones.