24. The transverse (T) tubules are. __ A) An extensive network of the muscle cell membrane that invaginates deep into the muscle fiber. B) Enlargement of terminal sarcoplasmic reticulum that wraps the sarcomeres. C) Bigg er in the smooth muscle, then in skeletal muscles D) Contain Na+ voltage-gated channel E) All of above

The correct answer is:<br /><br />D) Contain $Na+$ voltage-gated channels<br /><br />Transverse (T) tubules are invaginations of the muscle cell membrane (sarcolemma) that penetrate deep into the muscle fiber. They play a crucial role in muscle contraction by facilitating the rapid transmission of action potentials from the cell surface to the interior of the muscle fiber. T tubules contain voltage-gated sodium channels that allow the influx of sodium ions, contributing to the depolarization of the muscle cell membrane and the initiation of the muscle contraction process.