J. Adam Noah

Date of Award

2003

Degree Name

Doctor of Philosophy

College

College of Liberal Arts

Type of Degree

Ph.D.

Document Type

Dissertation

First Advisor

Sasha N. Zill

Second Advisor

William Rhoten

Third Advisor

Rudy Wang

Fourth Advisor

Monica Valentovic

Fifth Advisor

Todd Green

Abstract

Sense organs in the legs that detect body weight are an important component in the regulation of posture and locomotion. This thesis seeks to gain an understanding of how body weight is detected by sense organs of the legs, and determine how this information influences muscle activities in standing and walking. The first study tested the ability of tibial campaniform sensilla (receptors that monitor forces in the cockroach leg) to encode variations in body load using magnets attached to the thorax. Recordings of sensory activities in freely standing animals showed that proximal tibial sensilla (oriented perpendicular to the leg long axis) encode the level of body load while distal receptors (oriented parallel) fired to decreasing loads. In some postures, sensillum discharges paralleled changes in activity of the trochanteral extensor muscle consistent with a known interjoint reflex. These findings demonstrate that tibial campaniform sensilla can monitor the effects of body weight upon the legs and may aid in generating support of body load.

In the second study, sensory activities were compared when animals walked freely in an arena, or upon an oiled glass plate with their body weight supported. Sensilla discharges persisted but were abbreviated when body load was reduced. The results suggest that sensory discharges early in stance result from forces generated by contractions of muscles that press the leg against the substrate. Force feedback later in stance may adjust motor output to changes in loading.

In the third study, muscle activities and leg movements were recorded before and after denervation of distal leg segments. Regular bursts occurred in motoneurons to leg extensor muscles following denervation, including ‘fictive’ bursting in a muscle whose tendon (apodeme) was cut in the ablation. Similar motoneuron activities were found in walking on an oiled glass surface, when effects of body weight and mechanical coupling were minimized. When distal segments were completely severed, leg use and muscle bursting were disrupted but could be restored if the stumps were pressed against the substrate. These results support the hypothesis that feedback from receptors in proximal leg segments, that indicate forces, allow for active leg use in walking.

Subject(s)

Cockroaches -- Physiology.

Cockroaches -- Neurophysiology.

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