Tuning posture to body load: decreases in load produce discrete sensory signals in the legs of freely standing cockroaches

Abstract

Decreases in load are important cues in the control of posture and walking. We recorded activities of the tibial campaniform sensilla, receptors that monitor forces as strains in the exoskeleton, in the middle legs of freely moving cockroaches. Small magnets were attached to the thorax and body load was changed by applying currents to a coil below the substrate. Body position was monitored by video recording. The tibial sensilla are organized into proximal and distal subgroups that have different response properties and reflex effects: proximal sensilla excite extensor motoneurons while distal receptors inhibit extensor firing. Sudden load decreases elicited bursts from distal sensilla, while increased load excited proximal receptors. The onset of sensory discharges closely approximated the time of peak velocity of body movement in both load decreases and increases. Firing of distal sensilla rapidly adapted to sustained unloading, while proximal sensilla discharged tonically to load increases. Load decreases of small amplitude or at low rates produced only inhibition of proximal activity while decrements of larger size or rate elicited distal firing. These response properties may provide discrete signals that either modulate excitatory extensor drive during small load variations or inhibit support prior to compensatory stepping or initiation of swing.

Force encoding in stick insect legs delineates a reference frame for motor control

“…These basic response characteristics are similar to those found in multiunit recordings of trochanteral campaniform sensilla of cockroaches ) and in recordings of identified receptors in tibial sensilla of stick insects (Zill et al 2010), cockroaches (Ridgel et al 2000), and locusts (Burrows and Pflüger 1988). In addition, discharges to decreases in force have been extensively studied in campaniform sensilla in cockroaches (Keller et al 2007;Ridgel et al 1999) and locusts (Newland and Emptage 1996) and in receptors of vertebrates (Trulsson 2001). Signals of force decreases are important cues at the end of the stance phase of walking and can indicate leg slipping and loss of substrate adherence (Duysens et al 2000).…”

“…Vigorous sensory discharges were recorded in the nervus cruris when forces were applied to the femur in a dorsal direction (levation of the CTr joint) using half-sine waveforms ( Fig. 3A; as in Keller et al 2007). The largest units typically fired phasically during the rising phase of the stimulus.…”

Effects of force detecting sense organs on muscle synergies are correlated with their response properties

“…These specific legs were utilized to extend findings of previously published studies (Zill et al, 2012; 2015a, b). While the legs are of different body segments, the distribution, number and responses of campaniform sensilla are quite similar in middle and hind legs in both species (Hofmann and Bässler, 1982, 1986; Keller et al, 2007; Zill et al, 2009). Studies of the functions and forces generated by the legs also indicate that they serve similar functions in support and propulsion, although the hind legs are normally the major source of propulsive forces in the cockroach escape reaction (Hughes, 1952; Dallmann et al, 2016).…”

Proprioceptors involved in stinging response of the honeybee, Apis mellifera

“…In the cockroach, for example, sensilla responding to an increase or decrease in the force of the legs contribute to the onset of swing and reinforce leg coordination during walking (Keller et al, 2007;Ridgel et al, 1999;Noah et al, 2001Noah et al, , 2004Zill et al, 2009). In our experiments, the pinching stimulus to the campaniform sensilla situated on the sting evoked the stinging response, and the stinging movement was sustained for as long as the sting was pinched.…”