Question

During excitation-contraction coupling in cardiac myocytes _____

multiple choice question.
A. extracellular fluid Ca₂ enters through l-type Ca₂ channels and triggers Ca₂ release from the sarcoplasmic reticulum through ryanodine receptors
B. extracellular fluid Ca₂ enters through ryanodine receptors and triggers Ca₂ -release from the sarcoplasmic reticulum through l-type ca2 channels sarcoplasmic
C. reticulum Ca₂ exiting through l-type Ca₂ channels triggers the entry of extracellular fluid Ca₂ through ryanodine receptors sarcoplasmic
D. reticulum Ca₂ exiting through ryanodine receptors triggers the entry of extracellular fluid Ca₂ through l-type Ca₂ channels

Answer 1

In cardiac myocytes, the process of excitation-contraction coupling involves the entry of extracellular fluid Ca2+ through L-type Ca2+ channels which triggers the release of Ca2+ from the sarcoplasmic reticulum through ryanodine receptors, leading to muscle fiber contraction. The correct answer is option A.

Step-by-step explanation:

During excitation-contraction coupling in cardiac myocytes, extracellular fluid Ca2+ enters through L-type Ca2+ channels and triggers Ca2+ release from the sarcoplasmic reticulum through ryanodine receptors. This process involves the propagation of an action potential along the sarcolemma, which subsequently triggers the opening of these calcium channels in the sarcoplasmic reticulum, allowing for the diffusion of Ca2+ into the sarcoplasm. The increase in Ca2+ concentration in the sarcoplasm initiates the interaction with troponin in the troponin-tropomyosin complex, facilitating the contraction of the muscle fiber by allowing myosin to form cross-bridges with actin.