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Journal of Experimental Biology 56,509-525 (1972)
Published by Company of Biologists 1972

An Analysis of the Types of Sensory Unit Present in the PD Proprioceptor of Decapod Crustaceans

P. J. MILL ¹ and D. A. LOWE ¹

¹ Department of Zoology, University of Leeds

1. The PD organs of various decapod crustaceans were stimulated by elongation and relaxation of the strand, and single-unit recordings were made from the different types of sensory unit.

2. The sensory units can all be placed in one or other of three categories: unidirectional movement cells, position cells and intermediate cells.

3. Unidirectional movement cells are large, phasic units which respond either to elongation or relaxation of the strand. Some are pure movement-sensitive units, which reach saturation at very low movement velocities and fire over most or all of the range of movement. Other units show velocity sensitivity and differential range sensitivity in varying degrees.

4. Position cells are small tonic units and are usually maximally sensitive at one end of the range of movement. Their firing pattern is asymmetric in that the frequency of impulses is dependent on the direction of movement by which a given position is achieved.

5. Intermediate cells have large phasic and tonic components which may or may not show a direct relationship to each other.

6. The importance of the detailed information produced by the PD organ is discussed and suggestions made as to how it could be utilized by the central nervous system.