Date of Award

Spring 4-26-2013

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Biology

First Advisor

Donald H. Edwards

Second Advisor

Paul S. Katz

Third Advisor

Walter W. Walthall

Abstract

During centrally orchestrated movements, the nervous system must distinguish between appropriate and inappropriate reflexes. I studied local postural flexion reflexes of the crayfish that are evoked by unexpected touch. An isolated abdomen was used which permitted recording and stimulating of tailfan afferents, nerve cord interneurons, and postural motor neurons. Stimulation of the afferents evoked a postural flexion response of the medium tonic and large phasic motor neurons of the superficial flexor nerve; a flexion motor program was then excited by stimulating descending interneurons. Afferent stimulation evoked a smaller motor response during the motor program than before or after. These results indicate that the postural reflex responses to sensory stimulation are inhibited at a site presynaptic to the motor neurons during the flexion motor program. Application of Picrotoxin (blocked inhibition) to the primary afferent-to-mechanosensory interneuron synapse did not prevent the modulation of the postural flexion reflex during the flexion motor program.

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