Summary
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1.
Single statolith-hair and free-hook-hair receptors were studied in isolated parts of the statocyst of the crabScylla serrata.
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2.
Upon deflection of single hairs the responses of the statolith-hair and free-hook-hair receptors are essentially similar. The receptors have a phasic-tonic response pattern (Figs. 5B and 12), a fan-shaped directionality (Figs. 3, 8B and 11), and their stimulus-response plots saturate (Figs. 6 and 13).
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3.
Statolith and free-hook hairs bend most easily in the plane formed by the hair and its hook. The main sensitivity of the receptors is in this plane and into or opposite to the direction in which the hooks point (Figs. 3 and 11).
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4.
The hooks of the great majority of the free-hook hairs are directed dorso-ventrally (Fig. 11D). The position of the hairs relative to the statocyst wall is not affected by gravity. On the basis of the anatomy of the hairs and the properties of their receptors it is suggested that the free-hook-hair receptors provide the crab with a system which measures head-up movements independent of the position of the body in space.
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5.
The statolith hairs are arranged in two concentric rows. Their hooks point to the centre, perpendicular to the rows of hairs. When stimulated by displacing the statolith the hair receptors of the inner row respond phasically (Figs. 4 and 5). The directionality (Fig. 3) and stimulus-response plots (Fig. 6) of the receptors when stimulated by displacing the statolith are similar to those of receptors stimulated by deflecting single hairs. It is concluded that the hair receptors of the inner row inform the crab about the direction and amplitude of the positional changes but that they can not code for the absolute position of the body in space.
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6.
The response properties of the hair receptors of the outer row are affected to a great extent by the attachment of the statolith to the hairs. Low-frequency lateral displacements of the statolith into any direction suppress the activity of the receptors (Fig. 8A). High-frequency statolith displacements or vibrations activate the hair receptors (Fig. 7). The significance of these response properties for the function of the hair receptors of the outer row in eye withdrawal behaviour of the crab is discussed.
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The author thanks the Free University of Amsterdam and the IBRO for financial support, the members of the Department of Biology (Division Zoology) of the Free University, Amsterdam for reading the manuscript, Mr. G.W.H. van den Berg and Mr. C. van Groenigen for their help in preparing the figures and Mrs. P.F.M. Ohr-Bulder for typing the manuscript.
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Janse, C. The function of statolith-hair and free-hook-hair receptors. J. Comp. Physiol. 137, 51–62 (1980). https://doi.org/10.1007/BF00656917
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DOI: https://doi.org/10.1007/BF00656917