title: Detecting substrate engagement: responses of tarsal campaniform sensilla in cockroaches.
abstract: Sensory signals of contact and engagement with the substrate are important in the control and adaptation of posture and locomotion. We characterized responses of campaniform sensilla, receptors that encode forces as cuticular strains, in the tarsi (feet) of cockroaches using neurophysiological techniques and digital imaging. A campaniform sensillum on the fourth tarsal segment was readily identified by its large action potential in nerve recordings. The receptor discharged to contractions of the retractor unguis muscle, which engages the pretarsus (claws and arolium) with the substrate. We mimicked the effects of muscle contractions by applying displacements to the retractor apodeme (tendon). Sensillum firing did not occur to unopposed movements, but followed engagement of the claws with an object. Vector analysis of forces suggested that resisted muscle contractions produce counterforces that axially compress the tarsal segments. Close joint packing of tarsal segments was clearly observed following claw engagement. Physiological experiments showed that the sensillum responded vigorously to axial forces applied directly to the distal tarsus. Discharges of tarsal campaniform sensilla could effectively signal active substrate engagement when the pretarsal claws and arolium are used to grip the substrate in climbing, traversing irregular terrains or walking on inverted surfaces.
authors.affiliation: Department of Anatomy and Pathology, Joan C. Edwards School of Medicine, Marshall University, Huntington, WV 25704, USA. sensillum@aol.com
authors.forename: Sasha N
authors.initials: SN
authors.lastname: Zill
authors.forename: Bridget R
authors.initials: BR
authors.lastname: Keller
authors.forename: Sumaiya
authors.initials: S
authors.lastname: Chaudhry
authors.forename: Elizabeth R
authors.initials: ER
authors.lastname: Duke
authors.forename: David
authors.initials: D
authors.lastname: Neff
authors.forename: Roger
authors.initials: R
authors.lastname: Quinn
authors.forename: Clay
authors.initials: C
authors.lastname: Flannigan
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000222:Adaptation, Physiological / Q000502:physiology; D000818:Animals; D003058:Cockroaches / Q000033:anatomy & histology / Q000502:physiology*; D004576:Electromyography / Q000379:methods; D008465:Mechanoreceptors / Q000502:physiology*; D009068:Movement / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology; D010812:Physical Stimulation / Q000379:methods; D011930:Reaction Time / Q000502:physiology; D011984:Sensory Receptor Cells / Q000502:physiology*; D013643:Tarsus, Animal / Q000502:physiology* / Q000648:ultrastructure
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