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KMID : 0376219740110010227
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Chonnam Medical Journal
1974 Volume.11 No. 1 p.227 ~ p.235
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Synergic action of retractor oculi to the rectus muscles in the rabbits
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Chung Young-Tae
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Abstract
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Although many mammals are known to have the retractor oculi muscles, the function of the muscles are not clearly defined. Some authors are in favor of the concept that the muscles retract the eye balls for protection of the external eye. The other explanation is that the muscles are used to pull back the eye balls against the gravity when the animals are in head down and grazing postures. On the other hand, recent experimental observations of Shim(1973) suggested that the muscles can act as the rotators as the other extraocular muscles.
In this experiments employing the urethane anesthetized rabbits, vestibular canal nerves were subjected to square wave stimuli, and the isometric as well as the EMG responses of the retractor muscle slips were recorded by means of a physiographic recorder. Vestibular responses of the muscles were summarized as follows.
1. All the retractor oculi slips revealed vestibular reflex responses, contraction or relaxation, depending upon which vestibular system was stimulated.
2. The antagonistic effects were demonstrated between the superior and inferior slips as well as between the medial and lateral slips.
3. Superior and medial slips were excited by the stimulation of ipsilateral vestibular canals and were inhibited by contra lateral canals. In contrast, inferior and lateral slips were excited by the stimulation of contra lateral canals and were inhibited by ipsilateral canals.
4. In recording these vestibular responses of the muscles, EMG activities sometimes better reflected the slight inhibition of the muscles than the isometric tension record.
Based on the above experimental observations it is inferred that the retractor oculi muscles may have an ocular rotatory action in addition to the retractive role. The individual retractor slip seems to be synergic to the adjacent rectus muscle for instance, the medial and lateral slips may act as the synergists to the medial, and lateral rectus respectively for the horizontal rotation of the eye balls.
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