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Title: Investigations on the innervation of the diaphragm in cats and rodents, with special reference to the phrenic nerve in cats
Author: Wilson, A. S.
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1967
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This thesis is a morphological study of the innervation of the diaphragm in cats and rodents. The observations are based on preparations of normal material as well as material taken at different periods following selective partial denervation of the diaphragm. At the outset it was considered desirable to carry out quantitative investigations on the fibre components of the phrenic nerves in normal animals so that criteria could be established for subsequent comparison of neurohistological observations. Myelinated fibres within the nerve were clearly demonstrated in osmium preparations and quantitative studies, carried out at three separate levels, indicated a distinct increase in fibres of larger diameter (12-18mu) in the peripheral third of the intrathoracic part of the nerve trunk. This observation raised the possibility that the phrenic nerve receives an accession of fibres from an extra-phrenic source close to its termination within the thorax. No correspondingly reliable method could be found for quantitative studies on the smallest neural components which are commonly called unmyelinated fibres. It was necessary, therefore, to devise a more reliable method before any systematic investigation could be -undertaken. A new ultrastructural technique for demonstrating the components within a transverse section of the phrenic nerve in cats was developed and its mode of employment is described. Its evaluation and characteristics are discussed in the list of previous histological findings. The new method can be used to determine the absolute numbers of nerve fibres and vascular components present at one particular level within the phrenic nerve. The general arrangements of the diaphragmatic plexus, demonstrated by silver impregnation of whole preparations in mice and rats were compared with the findings in frozen sections of the diaphragm in cats. Detailed studies on the participation of various peripheral nerves in the innervation of the diaphragm can be demonstrated only after selective denervation. It was necessary, therefore, to establish the time course of the changes following these operative procedures and to determine the optimvim survival period applicable to this method of investigation. After unilateral intrathoracic transection of the phrenic nerve in cats, a small number of axis cylinders persist within the otherwise degenerating portion of the nerve peripheral to the level of the lesion and within the area of the diaphragm which is normally supplied by the homolateral phrenic nerve. This is in general agreement with the peripheral increase in numbers of myelinated fibres found within the phrenic nerves of normal animals and further experimental procedures were designed to investigate the possible existence of such an accession and to define its source. While unilateral extirpation of the coeliac ganglion induced very limited changes within the diaphragmatic nerve plexus, ligation of the dorsal roots of the caudal six thoracic segmental nerves central to the spinal ganglion indicated widespread participation of these nerves in the innervation of the diaphragm. Finally, following separation of the peripheral third of the intrathoracic part of the intact phrenic nerve from its subjacent connective tissue, degenerative changes were observed in the nerve fibres within the homolateral diaphragmatic plexus. In view of these findings it seems reasonable to suggest that the phrenic nerve receives an accession of nerve fibres at this level and that they may arise from the spinal cord in the region of origin of the caudal six thoracic segmental nerves.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (M.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available