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Developing muscle spindles in the mouse masseter muscle studied by electron microscopy.
The Bulletin of Tokyo Medical and Dental University
|March 1, 1987
Summary
This study details the development of mouse masseter muscle spindles from fetal to adult stages. Key findings reveal the timing of sensory nerve endings, muscle fiber fusion, and capsule formation during early development.
Area of Science:
- Developmental Biology
- Neuroscience
- Histology
Background:
- Muscle spindles are sensory mechanoreceptors crucial for proprioception.
- The development of the masseter muscle spindle is not well-documented.
- Understanding morphogenesis aids in comprehending neuromuscular function.
Purpose of the Study:
- To investigate the electron microscopic morphogenesis of the masseter muscle spindle in mice.
- To determine the developmental timeline of key components including nerve terminals, muscle fibers, and capsule formation.
Main Methods:
- Electron microscopy was used to examine masseter muscle spindles.
- Tissues were collected from mice at various developmental stages: 16-day fetuses to 4-day-old young, and 3-month-old adults.
- Morphological changes were analyzed at the cellular and subcellular levels.
Main Results:
- Masseter muscle spindle formation begins by the 16th fetal day.
- Sensory nerve terminals associate with myoblasts and myotubes.
- Intrafusal muscle fibers likely form via myocyte fusion; gamma motor end-plates appear later.
- Inner capsule formation, periaxial space development, and nerve myelination occur in early postnatal life.
- Extrafusal muscle fibers also show significant development concurrently.
Conclusions:
- The masseter muscle spindle undergoes complex morphogenesis from fetal to early postnatal stages.
- Coordinated development of muscle spindles, nerve fibers, and extrafusal muscle fibers occurs during a critical early postnatal period.
- The study provides a detailed timeline for the formation of these neuromuscular structures.