Hair plate

Hair plates are a type of mechanoreceptor found in insects. Hair plates are tightly packed groups of sensory hairs that sense movements of one body segment relative to an adjoining segment. Hair plates are considered external proprioceptors.
Structure.
Hair plates typically consist of several dozen individual sensory hairs. Each hair is innervated by a single sensory neuron (see schematic cross-section).
Hair plates are often positioned next to folds within the cuticle, so that hairs are deflected during joint movement. Hair plates are located on different body parts, including the legs, the neck, and the antennae.
Function.
Hair plates function as proprioceptors. The sensory neurons innervating the hair plate may respond phasically to hair movements (rapidly adapting) or tonically to maintained deflections (slowly adapting). Thus, hair plates can encode the position and movement of an adjoining body segment. Hair plate neurons project to the insect central nervous system, where they form synapses with multiple postsynaptic partners. They can provide direct excitatory and indirect inhibitory input to motor neurons as well as presynaptic inhibition to other proprioceptors.
Hair plates located at the leg joints provide sensory feedback for the control of walking. In stick insects and cockroaches, the surgical removal of a hair plate on the proximal leg causes the leg to overstep and collide with the leg in front, indicating that proprioceptive signals from the hair plate limit the forward movement of the leg. This “limit detector” function is similar to that of mammalian joint receptors. 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. 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.
Hair plates located on the proximal segments of the antenna (see schematic) provide sensory feedback for the control of antennal movement and are thought to play an important role in active sensing, object localization, and targeted reaching movements.