CONTRIBUTION OF MOTOR NEURON INTRINSIC PROPERTIES TO MOTOR PATTERN GENERATION Open Access

Wright, Jr., Terrence Michael (2011)

Permanent URL: https://etd.library.emory.edu/concern/etds/db78tc72k?locale=en
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Abstract

Rhythmic motor patterns, such as walking, are generated, in part, by
rhythmically active neural networks called central pattern generators (CPG's;
Marder and Calabrese, 1996). Typically, CPG's provide rhythmically patterned
synaptic drive onto motor neurons in order to coordinate them, with appropriate
phase differences, into a motor pattern appropriate for the behavior. These
premotor patterns of drive contain both timing information and patterns of
synaptic strengths. Invertebrate preparations, with their simple and accessible
nervous systems, have been used to generate principles that underlie how
premotor patterns of synaptic input interact with motor neurons to produce
stereotyped motor outputs (Marder and Bucher, 2007). Here, I use the leech
heartbeat CPG, a system in which patterns of synaptic drive onto motor neurons
can be easily measured, to address how a CPG circuit coordinates its motor
neurons to produce stereotyped motor patterns.
In the first of two studies, I show that, although the segmental input
pattern is the primary determinant of motor neuron output, the intrinsic
properties of the heart motor neurons play an important role in determining how
they are coordinated by their segmental synaptic input pattern, particularly when
receiving one of the two input patterns these motor neurons receive.
In the second study, I show, in both modeling and in follow-up
experiments in the living system, that the generation of one motor pattern is a
consequence of the nearly synchronous premotor timing information produced
by the leech heartbeat CPG. For the other motor pattern, I show that premotor
timing information determines the range over which motor neurons can fire
while synaptic strength profiles define the actual motor progression.
These experiments provide a direct assessment of how motor neuron
intrinsic properties interact with their premotor pattern of synaptic drive to
produce rhythmic motor output. Furthermore, the data presented here may
inform studies on motor pattern generation in other systems, including studies
on recovery of locomotor control in patients with spinal cord injury.

Table of Contents

TABLE OF CONTENTS







PAGE
CHAPTER
1:
GENERAL
INTRODUCTION
1
CHAPTER 2: CONTRIBUTION OF MOTOR NEURON INTRINSIC
PROPERTIES TO FICTIVE MOTOR PATTERN GENERATION

27
CHAPTER 3: Patterns of presynaptic activity and synaptic strength interact to
produce
motor
output
93
CHAPTER
4:
GENERAL
DISCUSSION
167
APPENDIX








192
REFERENCE LIST







200


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