A better understanding of the motor control of the pharynx would provide insight into a number of clinically important paryngeal movement disorders. The unique location of the pharynx at the intersection of the upper respiratory and digestive tracts bestows it with important roles in swallowing and respiration. Additionally, in humans, parts of the pharynx are delicately controlled during speech to alter the acoustic properties of the vocal tract. Hence weakness, incoordination of paralysis of the pharynx severely impacts basic communicative and life-sustaining functions. This application seeks to establish a research program to investigate basic issues of motor control as they relate to the special features of the pharyngeal musculature. Related work in this and other motor systems has stimulated a number of questions concerning the anatomy and function of pharyngeal motor units. A series of projects are proposed which would build upon each other in a logical sequence: first, muscle architecture will be described by reconstructing the three-dimensional anatomy of the pharyngeal muscles from serial sections. Further basic anatomical work will be done to determine the extent to which the muscle is functionally and structurally subdivided, by examining fiber histochemistry, nerve branch innervation territories, and motor endplate distributions. Next, muscle architecture will be correlated with the activity patterns of its constituent motor units by mapping the locations and response properties of single motor units as determined by a variety of reflex-elicited stimuli. In parallel with the mapping work, retrograde tracers will be injected into physiologically defined subdivisions of the muscle to relate the location and morphology of sub-populations of pharyngeal motoneurons in the brainstem to the functional architecture of the muscle. Finally, experiments will be conducted to see if pharyngeal motoneurons share common response properties with other non-pharyngeal motoneurons with which they are closely associated anatomically in the brain.
