Membranous channel extending inward from muscle fiber membrane

The correct answer is - transverse tubules.

Explanation:

Transverse tubules are the membranous channel that extends inward from the muscle cell, these are the actually the addition or extensions of the cell membrane that invade into the center of muscles cells except smooth muscles.

The role of the transverse tubules is to generating the stimulus or signals from the sarcolemma to down in the cell. Sarcolemma are the surface of the cells in muscles.

Thus, the correct answer is - transverse tubules.