Skeletal Muscle Fiber Types and Proprioceptors Quiz

Proprioceptors and Muscle Function

• Proprioceptors detect increases in tension and help regulate the amount of effort required to perform movements that call for variable amounts of muscular force.

Skeletal Muscle Fiber Types

• There are three types of skeletal muscle fibers: Type I (slow oxidative), Type IIa (fast oxidative glycolytic), and Type IIb (fast glycolytic) fibers.
• Type I fibers are adapted for slow contractions over long periods without fatigue, with many mitochondria, surrounding capillaries, and myoglobin, making them dark or red in color.
• Type I fibers are particularly suited for maintaining erect posture and are found in high percentages in high-endurance athletes such as marathon runners.
• Type IIa fibers are intermediate fibers with many mitochondria and high myoglobin content, capable of anaerobic glycolysis, and are found in athletes such as 400- and 800-m sprinters, middle-distance swimmers, and hockey players.
• Type IIb fibers are large, light pink, and contain less myoglobin and fewer mitochondria than Type I and Type IIa fibers.

Development of Skeletal Muscle

• Myoblasts are derived from myogenic stem cells that originate in the embryo from unsegmented paraxial mesoderm (cranial muscle progenitors) or segmented mesoderm of somites.
• Skeletal muscle progenitors differentiate into early and late myoblasts.
• Early myoblasts form primary myotubes, chain-like structures with multiple central nuclei surrounded by myofilaments.
• Late myoblasts form secondary myotubes, characterized by more widely spaced peripheral nuclei and an increased number of myofilaments.

Repair of Skeletal Muscle

• Satellite cells are responsible for the skeletal muscle's ability to regenerate, but their regenerative capacity is limited.
• After muscle tissue injury, some satellite cells are activated and become myogenic precursors of muscle cells.

Muscle Structure

• Myofibrils consist of an end-to-end repetitive arrangement of sarcomeres.
• Sarcomeres exhibit an A and I banding pattern due to the regular arrangement of thick and thin myofilaments.
• The dark A band is bisected by a less dense, or light, region called the H band.
• The M line contains a myosin-binding protein myomesin that holds the thick filaments in place, and creatine kinase.
• Thick filaments consist primarily of myosin molecules, which are large complexes (~500 kDa) with two identical heavy chains and two pairs of light chains.
• Thin filaments primarily consist of polymerized actin molecules coupled with regulatory proteins and other thin filament-associated proteins.