Final answer:
The increased tension seen during tetanus is primarily explained by the increased concentration of calcium ions around the myofibrils, which promotes the formation of cross-bridges.
Step-by-step explanation:
During tetanus, the increased tension is primarily explained by the increased concentration of calcium ions around the myofibrils. When a skeletal muscle is stimulated to contract, calcium ions are released from the sarcoplasmic reticulum, and their presence allows the myosin heads to bind with the exposed active sites on the actin filaments, resulting in muscle contraction. Therefore, the increased concentration of calcium ions around the myofibrils promotes the formation of cross-bridges and enhances tension during tetanus.