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Title: Cutaneous sensory mechanisms in the spinal cord
Author: Brown, A. G.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1968
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SECTION I: THE PREVIOUS LITERATURE. The literature relevant to the subject of the thesis is reviewed. The review is limited to reports on cutaneous receptors, their afferent nerve fibres and those spinal cord mechanisms which are of general importance for sensory mechanisms. For the most part, the literature reviewed is of experiments on cats, the species used most for neuronhysiological experiments. The importance of adequate stimulation of identified receptors is stressed. SECTION II: CUTANEOUS AFFERENT FIBRE COLLATERALS IN THE DORSAL COLUMNS. Microelectrode recordings were made from cutaneous afferent fibre collaterals, in the lumbar dorsal column, which were antidromically excited from C 2. The types of cutaneous afferent unit having axon collaterals which ascend the dorsal columns to the dorsal column nuclei were identified. All dorsal column collaterals had slower conduction velocities than corresponding peripheral axons and the degree of slowing was determined by the class of unit. The differential slowing was confirmed by recording compound action potentials from various parts of dorsal column - peripheral nerve pathways. SECTION III: THE SPINOCERVICAL TRACT: TYPES OF UNIT AND THEIR STIMULUS-RESPONSE PROPERTIES. Microelectrode recordings were made from axons of the spinocervical tract, In anaesthetized, unanaesthetized decerebrate and unanaesthetized spinal cats. The properties of the units depended on the type of preparation used. Differences between decerebrate and spinal cats were assumed to be due to a descending neuronal system active in the decerebrate animal. The Btimulus-response relationship to hair movement was described by a Power function, for those units sensitive to hair movement. All spinocervical tract units responded to high skin temperatures (above about 40°C) with an increased frequency of discharge. Several types of primary cutaneous afferent unit which excite the spinocervical tract were identified. SECTION IV: MODALITY CODING IN THE SPINOCERVICAL TRACT, Examination of individual spinocervical tract cell discharges evoked by different forms of natural stimulation revealed differences characteristic for the stimulus type. It was concluded that the modality of a stimulus, as well as its intensity, can be coded in the discharge of a single spinocervical tract cell. SECTION V: CONTROL OF THE 8PIN0CERVICAL TRACT IN DECEREBRATE 'REPARATIONS. By means of a reversible cold block of the spinal cord, individual spinocervical tract units were examined in the decerebrate and in the spinal state, and the actions of the descending neuronal system were studied. The equivalence of unit types in the two preparations was established. The descending system acts to inhibit certain of the excitatory inputs to individual spinocervical tract cells, while at the same time it prevents many inhibitory actions on the cells, SECTION VI: GENERAL DISCUSSI0N. The properties of the two ascending pathways studied are compared. Some problems raised by the present work, and the possible functions of the spinocervical system, are discussed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available