Ultrastructure of the grasshopper proximal femoral chordotonal organ.

This paper, the first in a series concerning the neurobiology of sensory cilia, describes the ultrastructure of our chosen model system--the proximal femoral chordotonal organ (FCO) in pro- and mesothoracic grasshopper legs. The FCO is a bundle of 150-200 longitudinally oriented chordotonal sensilla. Each chordotonal sensillum is a mechanoreceptive unit that contains two bipolar neurons whose dendrites bear sensory cilia. The structure of the sensory cilia leads us to suggest that they are motile cilia that respond to the mechanical stimulus with an "active stroke" which excites a transducer membrane at the dendrite tip.