Hair plate
Hair plates are a type of proprioceptor found in the folds of insect joints.[1] They consist of a cluster of hairs, in which each hair is innervated by a single mechanosensory neuron. Functionally, hair plates operate as "limit-detectors" by signaling the extremes of joint movement,[2] which then drives reflexive leg movement.[3]
Hair plate location and anatomy
[edit]![](http://upload.wikimedia.org/wikipedia/commons/thumb/7/7a/Hair_plate.svg/220px-Hair_plate.svg.png)
Hair plates consist of a field of cuticular hairs, in which each hair is innervated by a single mechanosensory neuron[1] [4](Figure 1). Hair plates are positioned within folds of cuticle at joints, and the associated hairs are deflected during joint movement.[5] The number of hairs across and within hair plates can vary[6][7] and hair plates are found on different body parts, including the legs,[8][9][10][6][11] neck,[12][13] and antennae.[14][15] On the legs of insects, hair plates are found at the proximal joints (i.e. thorax-coxa, coxa-trochanter, and trochanter-femur joints) across the front, middle, and hind legs.
Hair plate neurons project into the ventral nerve cord where the arborize dorsally and around the leg neuromere.[16] Moreover, the neurons of the hair plates located at the thorax-coxa joint project through the ventral, dorsal, and accessory prothoracic nerves, whereas, other hair plate neurons on the leg project through the prothoracic leg nerve.[17][18] Lastly, the neurons from each hair plate may have distinct axonal morphologies.
Sensory encoding and feedback circuits
[edit]Hair-plates are proprioceptors[1] and provide information to the nervous system about the positional and movement state of the body and legs. Hair plate neurons come in two flavors, one that responds phasically (rapidly adapting) and another that responds tonically (slowly adapting) to transient or maintained deflections of the hairs.[11][19] These encoding properties enable hair plates to signal the position and movement of adjoining body or leg segments. Neurons associated with the longer hairs within a hair plate form direct, mono-synaptic excitatory chemical synapses with motor neurons[6] as well as synapses with non-spiking interneurons that provide inhibitory input onto antagonistic motor neurons.[20] Therefore, hair plates provide rapid feedback to control the movement direction of the leg they are located on. It remains unknown what information the smaller hairs of hair plates signal and what that information is used for in leg motor control. Hair plate neurons are also involved in the presynaptic inhibition to other proprioceptors.[21]
Hair plate feedback to control behavior
[edit]Walking
[edit]Hair plates located at the leg joints provide sensory feedback for the control of walking.[8][9][22][2][23][24][25] In stick insects and cockroaches, the surgical removal of coxa hair plates alter the extremes of leg movement in such a way that the leg may overstep and collide with an ipsilateral leg. Therefore, hair plates control the transition of leg movement direction as well as the extent to which legs travel during the step cycle.[8][22] This “limit-detector” function is similar to that of mammalian joint receptors.[26] Therefore, hair plates encode the extremes of joint movement during walking to precisely control the direction of leg movement.
Feeding
[edit]Mechanosensory information from front leg hair plates also contribute to the regulation of feeding behavior in fruit flies, Drosophila melanogaster[27]. Integration of hair plate mechanosensory information with olfactory information from antennal neurons control the proboscis extension reflex (PER) in flies. Thus, the sensory input from hair plates is integrated with the information from other sensory modalities to control behaviors beyond walking.
Posture
[edit]Hair plates located on the neck (known as the prosternal organ) monitor head position relative to the thorax and provide sensory feedback for the control of head posture.[12][13] In the blowfly Calliphora, surgical removal of the prosternal organ hairs on one side causes the fly to compensate by rolling the head toward the operated side.[12] These results suggest that the prosternal organ may be involved in gaze stabilization.
Hair plates on the legs have also been shown to be important for resting posture. The ablation of the anterior trochanteral hair plate on a stick insect leg did not alter the coordination between legs, but rather resulted in that leg being held higher.[28] Also, hair plates on the trochanter were shown to control the body height. Overall, in addition to controlling walking kinematics, hair plates are also involved in postural control.
Antennal movement
[edit]Hair plates located on the proximal segments of the antenna (Figure 2) provide sensory feedback for the control of antennal movement[15] and are thought to play an important role in active sensing, object localization, and targeted reaching movements[14][29].
![](http://upload.wikimedia.org/wikipedia/commons/thumb/b/b2/Cockroach_antenna.jpg/220px-Cockroach_antenna.jpg)
See also
[edit]References
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- ^ a b Bässler, U. (1977-06-01). "Sensory control of leg movement in the stick insect Carausius morosus". Biological Cybernetics. 25 (2): 61–72. doi:10.1007/BF00337264. ISSN 1432-0770. PMID 836915. S2CID 2634261.
- ^ Burrows, Malcolm (1996-09-26). The Neurobiology of an Insect Brain. Oxford University Press. ISBN 978-0-19-172441-1.
- ^ Pringle, J (1938). "Proprioception in Insects: III. The Function of the Hair Sensilla at the Joints". JEB. 15 (4): 467–473.
- ^ Pringle, J. W. S. (1938-10-01). "Proprioception In Insects: III. The Function Of The Hair Sensilla At The Joints". Journal of Experimental Biology. 15 (4): 467–473. doi:10.1242/jeb.15.4.467. ISSN 0022-0949.
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- ^ Petryszak, Anna (1994). "External proprioceptors on the legs of insects of higher orders". Acta Biologica Cracoveinsia. 36: 13–22.
- ^ a b c Wendler, Gernot (1964-03-01). "Laufen und Stehen der Stabheuschrecke Carausius morosus: Sinnesborstenfelder in den Beingelenken als Glieder von Regelkreisen". Zeitschrift für vergleichende Physiologie (in German). 48 (2): 198–250. doi:10.1007/BF00297860. ISSN 1432-1351. S2CID 37588295.
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- ^ a b Newland; Watkins; Emptage; Nagayama (1976). "The structure, response properties, and development of a hair plate on the mesothoracic leg of the locust". J Exp Biol. 64: 233–249.
- ^ a b c Preuss; Hengstenberg (1992). "Structure and kinematics of the prosternal organs and their influence on head position in the blowfly Calliphora erythocephala". J Comp Physiol. 171: 483–493. doi:10.1007/BF00194581. S2CID 13379331.
- ^ a b Paulk; Gilbert (2006). "Proprioceptive encoding of head position in the black soldier fly, Hermetia illucens". J Exp Biol. 209 (Pt 19): 3913–3924. doi:10.1242/jeb.02438. PMID 16985207. S2CID 12169844.
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- ^ Cruse, H.; Dean, J.; Suilmann, M. (1984-09-01). "The contributions of diverse sense organs to the control of leg movement by a walking insect". Journal of Comparative Physiology A. 154 (5): 695–705. doi:10.1007/BF01350223. ISSN 1432-1351. S2CID 2519441.
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- ^ Schütz, Christoph; Dürr, Volker (2011-11-12). "Active tactile exploration for adaptive locomotion in the stick insect". Philosophical Transactions of the Royal Society B: Biological Sciences. 366 (1581): 2996–3005. doi:10.1098/rstb.2011.0126. ISSN 0962-8436. PMC 3172591. PMID 21969681.