Proprioceptors

Proprioceptors are sense organs able to respond continuously to deformations (changes in length) and stresses (tensions and compressions) in the body. They provide an organism with information on posture and position. Five types of proprioceptors occur in insects: hair plates, campaniform sensilla, chordotonal organs, stretch receptors, and nerve nets. In common, they respond tonically and adapt very slowly to a stimulus.

FIGURE 12.2. Hair plate at joint of coxa with pleuron. [After J. W. S. Pringle, 1938, Proprioceptors in insects. III. The function of the hair sensilla at the joints, J. Exp. Biol. 15: 467-473. By permission of Cambridge University Press, London.]

pleuron pleuron

coxa
FIGURE 12.3. (A) Campaniform sensillum; and (B) section through tip of campaniform sensillum to show stiffening rod of cuticle running along cuticular plate present in some species. [After V. G. Dethier, 1963, The Physiology of Insect Senses, John Wiley and Sons, Inc. By permission of the author.]

A campaniform sensillum (Figure 12.3A) includes all of the components of a tactile hair with which it is homologous except for the hair shaft, which is replaced by a dome-shaped plate of thin cuticle. The plate may be slightly raised above the surrounding cuticle, flush with it, or recessed, but in all cases it is contacted at its center by the distal tip of the neuron and serves as a stretch or compression sensor. In many species the plate is elliptical and has a stiffening rod of cuticle running longitudinally on the ventral side, to which the neuron tip is attached (Figure 12.3B). The sensillum shows directional sensitivity, being stimulated by stress perpendicular to the longitudinal axis of the rod. Typically, the sensilla are arranged in groups. In Periplaneta, for example, the sensilla of the tibia occur in two groups, with their rod axes at right angles. During walking (Chapter 13, Section 2.3), contraction of the flexor and extensor muscles stimulates the proximal and distal groups of sensilla, respectively, which are thus important in the overall coordination of the process. In addition, when the insect is standing, the proximal sensilla whose axes are perpendicular to the axis of the tibia are continuously stimulated because of the stress in the cuticle. Information from sensilla passes to the central nervous system where it inhibits the so-called "righting reflex." When the insect is turned on its back there are no longer stresses in the cuticle, the sensilla are not stimulated, the righting reflex is not inhibited, and the insect undertakes a series of kicking movements in order to regain the standing position.

Chordotonal (scolophorous) sensilla (= scolopidia) (Figure 12.4A) are another widely distributed form of proprioceptor in insects. Unlike the sensilla discussed earlier, chordotonal sensilla lack a specialized exocuticular component, though, it should be emphasized, they are believed to be homologous with the sensillum trichodeum and other types of sen-silla. A distinctive feature of scolopidia is the scolopale, an intracellular secretion of the sheath cells surrounding the dendrite of the sensory cell, that is assumed to be important in the transduction of the stimulus. They are associated with the body wall, internal skeletal structures, tracheae, and structures in which pressure changes occur. Though they are found singly, more commonly they occur in groups. Chordotonal organs exist as strands of

chortlotonal ligament

FIGURE 12.4. (A) Single chordotonal sensillum; and (B) chordotonal organ. [After V. G. Dethier, 1953, Mechanoreception, in: Insect Physiology (K. D. Roeder, ed.). Copyright © 1953 John Wiley and Sons, Inc. Reprinted by permission of John Wiley and Sons, Inc.]

Beekeeping for Beginners

Beekeeping for Beginners

The information in this book is useful to anyone wanting to start beekeeping as a hobby or a business. It was written for beginners. Those who have never looked into beekeeping, may not understand the meaning of the terminology used by people in the industry. We have tried to overcome the problem by giving explanations. We want you to be able to use this book as a guide in to beekeeping.

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