Gastrocnemius muscle insertion via the Achilles tendon. The plantaris muscle and a portion of its tendon run between the two muscles, which is involved in "locking" the knee from the standing position. Since the anterior compartment of the leg is lateral to the tibia, the bulge of muscle medial to the tibia on the anterior side is actually the posterior compartment. The soleus is superficial to the mid-shaft of the tibia. 10% to 30% of individuals have a sesamoid bone called the "fabella" in the lateral (outer) head of gastrocnemius muscle. Along with the soleus muscle, the gastrocnemius forms half of the
Muscle muscle cells (myocytes), and each cell is encased within its own endomysium of collagen fibers. Thus, the overall muscle consists of fibers (cells) that are bundled into fascicles, which are themselves grouped together to form muscles. At each level of bundling, a collagenous membrane surrounds the bundle, and these membranes support muscle function both by resisting passive stretching of the tissue and by distributing forces applied to the muscle. Scattered throughout the muscles are muscle spindles that provide sensory feedback information to the central nervous system. (This grouping structure is analogous to the organization of nerves which uses epineurium, perineurium,