Cortical Control of the Fusimotor System in the Tenuissimus Muscle of the Cat

Asgari-Khozankalaei, Alireza (1990) Cortical Control of the Fusimotor System in the Tenuissimus Muscle of the Cat. PhD thesis, University of Glasgow.

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Cortical control of the sensory output of muscle spindles was studied in anaesthetized cats in two series of complementary experiments. Gamma motoneurone activity was monitored during electrical stimulation of the sensorimotor cortex: a) by recording from single primary and secondary sensory afferents from the tenuissimus and flexor digitorum longus muscles in dorsal root filaments and b) by visualizing directly the movements of intrafusal muscle fibres in exteriorised muscle spindles of the tenuissimus muscle. It was found that the state of anaesthesia was crucial in obtaining reproducible results and variation in the state of anaesthesia can alter the fusimotor effect from static to dynamic or even from excitation to inhibition. This is consistent with findings of Vedel and Mouillac-Baudevin (1970). The anaesthetic agent used was also important in determining the magnitude and type of the response to electrical stimulation. The initial burst of the primary afferent in response to passive stretch was by far greater with chloralose than with barbiturate anaesthesia in both tenuissimus and flexor digitorum longus muscles, suggesting that there may be a tonic low-level dynamic gamma excitation in chloralose anaesthesia. The state of the sensorimotor cortex is important too. Prevention of CO2 escape from the surface of the cortex in the present experiments by covering the cortex with 1 cm of mineral oil is thought to be the sole factor which made these results different from those obtained by Gladden and McWilliam (1977a,b). Other new findings were 1) the topographical mapping of the sensorimotor cortex in relation to the type of gamma motoneurones recruited, static or dynamic, and 2) evidence for independent cortical control of different types of static gamma motoneurones: 1) A "dynamic area" was identified from which dynamic effects were clearly elicited during stimulation. The boundaries were the cruciate sulcus (anteriorly), the ansate sulcus (posteriorly) and the sagital longitudinal fissure (medially). Laterally, the area extended half way to the postcruciate dimple. In addition from direct observation of intrafusal fibre movements it was clear that dynamic gamma motoneurones were never recruited alone. 2) Static effects were elicited following stimulation of a much wider area across the sensorimotor cortex, the postcruciate dimple being almost at the centre. The sensorimotor cortex was not only capable of controlling static gamma motoneurones independently from dynamic ones, but also capable of simultaneously inhibiting some, static gamma motoneurones and exciting others, lending support to the idea (Boyd, 1986) that there is more than one type of static gamma motoneurone.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Physiology, Neurosciences
Date of Award: 1990
Depositing User: Enlighten Team
Unique ID: glathesis:1990-78126
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 28 Feb 2020 12:09
Last Modified: 28 Feb 2020 12:09

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