Final answer:
The temporal relation between cardiac AP calcium and tension during a twitch involves three phases: latent period, contraction phase, and relaxation phase. During the contraction phase, calcium ions interact with troponin and cross-bridges form, leading to increased tension.
Step-by-step explanation:
The temporal relation between cardiac action potential (AP) calcium and tension during a twitch can be described in three phases: latent period, contraction phase, and relaxation phase. During the latent period, the AP is propagating along the sarcolemma. In the contraction phase, calcium ions bind to troponin, tropomyosin moves away from actin-binding sites, cross-bridges form, and sarcomeres shorten, leading to increased tension. In the relaxation phase, tension decreases as calcium ions are pumped out of the sarcoplasm and cross-bridge cycling stops.