Question

question 50
during depolarization, ______________ rushes into the muscle fiber.
a k+ (potassium)
b troponin
c ca++ (calcium)
d na+ (sodium)

Explanation:

Depolarization in muscle fibers (and neurons) is mainly due to the influx of sodium ions (\(Na^{+}\)). When a stimulus is received, voltage - gated sodium channels open, and \(Na^{+}\) rushes into the cell, making the inside of the cell less negative (depolarizing it). Potassium (\(K^{+}\)) is mainly involved in repolarization (moving out of the cell). Calcium (\(Ca^{++}\)) has a role in muscle contraction (released from the sarcoplasmic reticulum after depolarization), but not in the initial depolarization. Troponin is a protein involved in the regulation of muscle contraction (interacts with tropomyosin and actin) and is not an ion that "rushes in" during depolarization.

Answer:

D. \(Na^{+}\) (sodium)