Final answer:
The role of dihydropyridine receptors (DHPRs) is to detect action potentials and facilitate the activation of ryanodine receptors (RyRs), which release calcium ions from the sarcoplasmic reticulum into the sarcoplasm, initiating muscle contraction.
Step-by-step explanation:
The roles of dihydropyridine and ryanodine receptors are crucial in the process of excitation-contraction coupling in muscle cells. Dihydropyridine receptors (DHPRs) are located on the T-tubules and are responsible for sensing the action potential that propagates along the sarcolemma. When an action potential arrives, DHPRs undergo a conformational change and directly interact with ryanodine receptors (RyRs), which are calcium release channels situated on the sarcoplasmic reticulum (SR). This interaction prompts the RyRs to open and release calcium ions (Ca2+) from the SR into the sarcoplasm. The influx of calcium into the sarcoplasm triggers the binding of calcium to troponin, causing a shift in the position of tropomyosin, which exposes the actin-binding sites to the myosin heads, allowing for muscle contraction.