Morphology and histochemistry of the ambiens muscle of the red-eared turtle Pseudemys scripta

✍ Scribed by John W. Hermanson; Paul R. Lennard; Richard L. Takamoto

• Publisher: John Wiley and Sons
• Year: 1986
• Tongue: English
• Weight: 822 KB
• Volume: 187
• Category: Article
• ISSN: 0362-2525
• DOI: 10.1002/jmor.1051870104

✦ Synopsis

Six fiber types have been described in the ambiens muscle of red-eared turtles. These include one slow oxidative type, two fast oxidative types, two fast oxidative and glycolytic types, and one fast glycolytic type. Fiber types are non-randomly distributed throughout cross sections of the muscle. There is a decreasing gradient of oxidative staining and a n increasing gradient of glycolytic staining along an axis from the superficial to deep regions of the muscle. The slow oxidative fibers are predominantly located within one or two fascicles of the superf~cial surface of the muscle. The fast glycolytic fibers are predominant in deep fascicles.

In contrast to previous reports of histochemically monotypic intrafusal fibers in turtle muscle, ambiens muscle spindles have been observed containing one to eleven intrafusal fibers, including two fiber types. Fiber diameter and area are consistently smaller than observed in most extrafusal fibers. Spindles are predominantly located in superficial and cranial fascicles of the ambiens muscle and are located in regions characterized by extrafusal fibers with high oxidative activity.

Recent studies have demonstrated that intramuscular divisions of labor exist and that particular muscle regions or muscular compartments may be especially suitable for the performance of selected tasks (Armstrong, '80; Gonyea and Ericson, '77; English and Letbetter, '82; Herring, et al., '79). Few studies have examined the intramuscular regional distribution of histochemically defined types of reptilian -muscle fibers. Some reptilian muscles contain fiber types comparable to the four fiber types found in mammalian muscle: fast glycolytic (FG), fast-oxidative glycolytic (FOG), fast intermediate (FD, and slow oxidative (SO) fibers (Peter, et al., '72; McDonagh, et al., ' 801, but most authors suggested that the reptilian "SO" fiber is a tonic