Sarcomere and Muscle Fiber Quiz: Skeletal Muscle Fiber Types

Study Notes

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.

Description

Test your knowledge on the three types of skeletal muscle fibers: Type I (slow oxidative), Type IIa (fast oxidative glycolytic), and Type IIb (fast glycolytic) fibers. Explore how proprioceptors regulate the amount of effort required for movements involving variable muscular force.