Structural organization of two fast, rhythmically active crustacean muscles

Area of Science:

• Crustacean muscle physiology
• Comparative myology
• Cellular ultrastructure

Background:

• The flagellum abductor and scaphognathite levator muscles of the green crab (Carcinus maenas) are crucial for respiration and feeding.
• These muscles exhibit high-frequency, long-duration rhythmic activity, suggesting specialized structural adaptations.

Purpose of the Study:

• To quantitatively compare the organization of the flagellum abductor and scaphognathite levator muscles in Carcinus maenas.
• To elucidate the structural basis for the high activity and fatigue resistance of these crustacean muscles.

Main Methods:

• Quantitative analysis using light and electron microscopy.
• Detailed examination of muscle fiber ultrastructure, including mitochondria, glycogen, myofibrils, and sarcoplasmic reticulum.

Main Results:

• Both muscles feature interconnected fibers forming fascicles with cytoplasmic continuity.
• Muscle fibers contain abundant mitochondria and glycogen, with contractile material comprising less than half the volume.
• Short sarcomeres (approx. 2 µm), a thin to thick filament ratio of ~3:1, and well-developed sarcoplasmic reticulum were observed.

Conclusions:

• The structural organization, particularly the extensive mitochondria and glycogen stores, supports the high activity and fatigue resistance of these muscles.
• A well-developed sarcoplasmic reticulum likely contributes to the capacity for high-frequency contractions.