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Increase in fibre numbers of the rat pterygoid muscles during postnatal growth
Insights
Pterygoid muscle fiber counts in male rats double by six weeks, then decrease slightly. Female rats have fewer medial pterygoid fibers than males, indicating sex-based differences in muscle development.
Area of Science:
- Anatomy
- Histology
- Developmental Biology
Background:
- The pterygoid muscles are crucial for mastication.
- Understanding their development is key to comprehending jaw mechanics.
Purpose of the Study:
- To quantify fiber number changes in rat pterygoid muscles during postnatal development.
- To investigate potential sex-based differences in muscle fiber development.
Main Methods:
- Histological analysis of pterygoid muscle transverse sections from rats of various ages.
- Fiber counting on enlarged photomicrographic prints.
Main Results:
- Medial pterygoid muscle fiber numbers doubled in males from birth to six weeks.
- A slight decrease (>10%) in fiber numbers occurred between six weeks and adulthood in both sexes.
- Male lateral pterygoid muscle fibers increased ~45% from birth to adulthood.
- Adult females had ~15% fewer medial pterygoid fibers than males; no sex difference in lateral pterygoid fibers.
- Muscle fiber precursors were observed in newborns, indicating postnatal fiber formation.
Conclusions:
- Pterygoid muscle development involves significant fiber number changes post-birth.
- Distinct developmental trajectories exist between medial and lateral pterygoid muscles.
- Sex-based differences emerge in the medial pterygoid muscle fiber count during development.
Abstract:
The total numbers of fibres in transverse histological sections of the pterygoid muscles of Lister rats of various ages were counted on enlarged photomicrographic prints. The number in the medial pterygoid of the male doubled between birth and six weeks. This was followed by a decrease of rather more than 10 percent in the numbers between six weeks and the adult stage in both males and females. The number of fibres in the lateral pterygoid of the male increased by about 45 percent between birth and the adult stage. There were about 15 percent fewer fibres in the medial pterygoid of the adult female than in the male; no such sex difference occurred in the lateral pterygoid. Early precursors of muscle fibres were seen in histological sections of these muscles in the newborn, confirming new fibre formation after birth. Such precursors gradually disappeared, starting with the most primitive, so that by the age of four weeks the muscles had a mature appearance.