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Title: The cutaneous sensory input to the spinocervical tract of the cat and the corticofugal modulation of transmission from the forelimb component
Author: Heath, Jeremy Peter
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1979
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Section I - Literature Review. The literature is reviewed with special reference to knowledge of cutaneous afferent fibres and their representation in spinocervical tract fibres in the lumbar spinal cord of the cat. Attention is drawn to the paucity of information about forelimb afferents and their representation on the cervical spinal cord. The control of transvision through ascending sensory pathways and in particular the spinocervical tract is discussed. Finally relevant work on the somatosensory cortex and corticofugal inhibition is reviewed and comment is made on the influence of anaesthetics on our knowledge of sensory mechanisms. Section II - Receptive Fields and Conduction Velocities of identified spinocervical tract axons in the cervical spinal cord. Recordings were made with micro-electrodes from single axons in the dorsolateral funiculus of the cervical spinal cord of decerebrate cats. Some of these axons could be designated on electrophysiological criteria as belonging to the spinocervical tract. Such axons conveyed tactile information qualitatively similar to that found by other workers in the lumbar cord. Quantitatively SGT axons with receptive fields in the forelimb were most common and were more frequently activated only by hair movement. Axonal conduction velocities were analysed in relation to the site and type of their afferent input. Section III - Homosegmental and heterosegmental inhibition of transmission through the spinocervical tract in decerebrate cats. Discharges evoked in SCT axons by electrical and natural stimulation were tested for inhibition from other cutaneous nerves both by electrical and natural stimulation. Inhibition was most easily elicited from the homologous limb and least easily from the heterologous contralateral limb. Conditioning curves of segmental inhibition were plotted and were consistent with a presynaptic mechanism. In two spinalised decerebrate cats, only homosegmental inhibition was found. Section IV - Ipsi- and Contralateral corticofugal inhibition of transvision through the spinocervical tract. Chloralose anaesthetised catarised cats were used to demonstrate corticofugal inhibition of spinocervical tract cells which were excited by electrical stimulation of the superficial radial nerve. Surface sprung ball stimulating electrodes were used to make a grid map of the cortical surface for areas of maximum inhibitory effect and glass micro-electrodes were used to stipulate the depth of the cortex. For both types of stimulation cathodal currents were most effective. Those areas of cortex eliciting most inhibition at a given current strength corresponded with the contralateral forelimb sensory receiving areas S.I and S. II. Weaker inhibition was elicited from the ipsilateral cortex. Conditioning curves of corticofugal inhibition were plotted.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available