Life and Medical Sciences
Cell & Developmental Biology
Wiley InterScience Backfile Collection 1832-2000
The tensor tympani muscle of the cat has been studied using histological and electrophysiological techniques. Histological studies revealed the presence of striated and smooth muscle fibers. The striated muscle fibers could be classified structurally as “Fibrillenstruktur” and “Felderstruktur” fibers, suggesting that both “fast” phasic and “slow” tonic fibers were present. Histochemical studies showed that some of the smaller (25-40 μ) Fibrillenstruktur fibers possessed relatively large end-plate receptor areas which stained heavily for acetylcholinesterase. The membranes and cytoplasm of even smaller diameter fibers (9-25 μ) stained for acetylcholinesterase, similar to its distribution in muscle spindles of other muscles.Intracellular recordings showed that there were two distribution peaks of the resting membrane potentials - one at 40-50 mV, the other at 70-80 mV. When the nerve to the tensor tympani was stimulated by single square wave pulses, small junctional potentials (40 mV) followed by an after-hyperpolarization, were recorded only from fibers with low resting membrane potentials - presumably slow Felderstruktur fibers. Large (70-90 mV) potentials which showed overshoot of zero potential, and which were preceded by initial long depolrizing potentials, were recorded from fibers with large resting membrane potentials. These fibers, which showed occasional spontaneous activity were presumably smooth muscle fibers. Potentials similar to those recorded from fast muscle fibers in other muscles were also occasionally recorded.It was concluded that the cat tensor tympani possessed slow and fast striated muscle fibers, smooth muscle fibers, and possible some embryonic type muscle fibers.
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