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RONALD L. KATZ, KENNETH E. EAKINS; Pharmacological Studies of Extraocular Muscles. Invest. Ophthalmol. Vis. Sci. 1967;6(3):261-268.
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The effects of neuromuscular blocking agents and anticholinesterases on the twitch and tonic neuromuscular systems of the superior rectus muscle and the twitch system of the tibialis anterior muscle were studied in pentobarbital-anesthetized cats. The twitch system is characterized by large-diameter nerve fibers, plaque-like nerve endings, and Fibrillenstruktur muscle fibers; the tonic system by small-diameter nerve fibers, grape-like nerve endings, and Felderstruktur muscle fibers. Depolarizing agents (succinylcholine, decamethonium, Imbretil) increased baseline tension of the superior rectus muscle by their effect on the tonic system. Nondepolarizing agents (d-tubocurarine, dimethyl tubocurarine, gallamine) and depolarizing agents decreased the ttoitch response of the superior rectus and tibialis anterior muscles by their effect on the twitch system. Anticholinesterases increased the baseline tension and twitch height of the superior rectus muscle, but had a variable effect on the twitch height of the tibialis muscle. It is suggested that saccadic eye movements are a function of the twitch system, while slow sustained activity of the eye is accomplished by the tonic system.
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