Some Observations on the Pattern of Labyrinth and Neck Reflexes and Their Interactions in Both Normal and Hemilabyrinthectomized Cats

Conway, Bernard A (1985) Some Observations on the Pattern of Labyrinth and Neck Reflexes and Their Interactions in Both Normal and Hemilabyrinthectomized Cats. PhD thesis, University of Glasgow.

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In this study the pattern of labyrinth and neck reflexes were examined in both acute hemilabyrinthectomized cats, and cats allowed to recover from the lesion. In acute animals it was found that labyrinth reflexes in extensors and flexors ipsilateral to the side of the lesion appeared normal, while labyrinth reflexes contralateral to the lesion were reversed in comparison to normal. Neck reflexes were unaltered by hemilabyrinthectomy. Consequently, labyrinth and neck reflex interactions are altered giving rise to a new pattern of interaction which may account for some of the observed postural abnormalities seen with hemilabyrinthectomy. Furthermore, the observation that the normal labyrinth reflex is dependant on the integrity of the contralateral labyrinth supports electrophysiological evidence that these reflexes are mediated predominantly by crossed pathways. In chronic cats, allowed a minimum of 8 weeks recovery, the labyrinth and neck reflexes contralateral to the original lesion regain their normal form, while labyrinth and neck reflexes on the side of the lesion, although normal in the extensor are reversed in the flexor muscles. The flexors and extensors on the side of the original lesion display parallel activity changes during labyrinth and neck reflexes. It therefore appears that in the compensated animal there has been a re-organisation of labyrinth and neck reflexes. The normal pattern has been restored to the limb contralateral to the lesion (which in the acute showed reversed reflexes), but in the limb ipsilateral to the lesion labyrinth and neck reflex expression in flexor muscles has been reversed giving coactivation of flexors and extensors. Despite this the complete pattern of labyrinth and neck reflexes in the compensated animal can still be considered appropriate for providing effective postural stabilisation by regulating the overal stiffness of one limb, and by altering the distribution of tone in the other, as in the normal reciprocal fashion. In addition to the above studies experiments were performed on both normal and acute decerebrated cats which examined the interaction of labyrinth and neck reflex systems with elbow joint afferents. In these experiments head, neck and elbow position was used to condition both crossed extensor and ipsilateral flexion reflexes. The results indicate that head and neck position modulate reflex excitability in flexors and extensors in a manner consistant with observations on the direction of labyrinth and neck reflexes in these muscles, and that elbow position can effectively modulate these actions independently of changes in muscle length. Extensor reflex excitability was greatest in normal cats when the elbow was flexed and the head tilted side-down or the neck tilted side-up. Flexor excitability was greatest with the limb held in extension and the head tilted side-up or the neck side-down. In acute animals the labyrinth actions were altered in agreement with the description of labyrinth reflexes in these animals. The ability of joint afferents to modulate descending labyrinth and neck inputs to motoneurones is taken to indicate that limb position can effectively regulate the reflex output of the labyrinth and neck systems so as to generate reflexes that are appropriate for the position of the limb at any particular time. (Abstract shortened by ProQuest.).

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Physiology
Date of Award: 1985
Depositing User: Enlighten Team
Unique ID: glathesis:1985-77380
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Jan 2020 09:10
Last Modified: 14 Jan 2020 09:10

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