Universität zu Köln

Zill, Sasha N., Dallmann, Chris J., Bueschges, Ansgar, Chaudhry, Sumaiya and Schmitz, Josef (2018). Force dynamics and synergist muscle activation in stick insects: the effects of using joint torques as mechanical stimuli. J. Neurophysiol., 120 (4). S. 1807 - 1824. BETHESDA: AMER PHYSIOLOGICAL SOC. ISSN 1522-1598

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Abstract

Many sensory systems are tuned to specific parameters of behaviors and have effects that are task-specific. We have studied how force feedback contributes to activation of synergist muscles in serially homologous legs of stick insects. Forces were applied using conventional half-sine or ramp and hold functions. We also utilized waveforms of joint torques calculated from experiments in freely walking animals. In all legs, forces applied to either the tarsus (foot) or proximal leg segment (trochanter) activated synergist muscles that generate substrate grip and support, but coupling of the depressor muscle to tarsal forces was weak in the front legs. Activation of trochanteral receptors using ramp and hold functions generated positive feedback to the depressor muscle in all legs when animals were induced to seek substrate grip. However, discharges of the synergist flexor muscle showed adaptation at moderate force levels. In contrast, application of forces using torque waveforms, which do not have a static hold phase, produced sustained discharges in muscle synergies with little adaptation. Firing frequencies reflected the magnitude of ground reaction forces, were graded to changes in force amplitude. and could also be modulated by transient force perturbations added to the waveforms. Comparison of synergist activation by torques and ramp and hold functions revealed a strong influence of force dynamics (dF/dt). These studies support the idea that force receptors can act to tune muscle synergies synchronously to the range of force magnitudes and dynamics that occur in each leg according to their specific use in behavior. NEW & NOTEWORTHY The effects of force receptors (campaniform sensilla) on leg muscles and synergies were characterized in stick insects using both ramp and hold functions and waveforms of joint torques calculated by inverse dynamics. Motor responses were sustained and showed reduced adaptation to the more natural and nonlinear torque stimuli. Calculation of the first derivative (dF/dt) of the torque waveforms demonstrated that this difference was correlated with the dynamic sensitivities of the system.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Zill, Sasha N. UNSPECIFIED UNSPECIFIED UNSPECIFIED Dallmann, Chris J. UNSPECIFIED UNSPECIFIED UNSPECIFIED Bueschges, Ansgar UNSPECIFIED UNSPECIFIED UNSPECIFIED Chaudhry, Sumaiya UNSPECIFIED UNSPECIFIED UNSPECIFIED Schmitz, Josef UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-170378
DOI:	10.1152/jn.00371.2018
Journal or Publication Title:	J. Neurophysiol.
Volume:	120
Number:	4
Page Range:	S. 1807 - 1824
Date:	2018
Publisher:	AMER PHYSIOLOGICAL SOC
Place of Publication:	BETHESDA
ISSN:	1522-1598
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language TIBIAL CAMPANIFORM SENSILLA; NATURALISTIC STIMULATION; REFLEX REVERSAL; SENSORY SIGNALS; MOTOR-ACTIVITY; BODY LOAD; WALKING; FEEDBACK; LEG; COCKROACH Multiple languages Neurosciences; Physiology Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/17037