Question

multiple choice: deep inward extensions of the sarcolemma form a tunnel - like network inside the muscle cell known as: a myofilaments b the sarcoplasmic reticulum c transverse tubules (t - tubules) d myofibrils

Explanation:

• Myofilaments: These are the contractile proteins (actin and myosin) within a muscle cell, not the tunnel - like network from sarcolemma extensions.
• Sarcoplasmic reticulum: It is a membrane - bound structure (a type of endoplasmic reticulum) that stores calcium ions, not formed by inward extensions of the sarcolemma.
• Transverse tubules (T - tubules): They are indeed deep inward extensions of the sarcolemma (the plasma membrane of the muscle cell) that form a tunnel - like network. They play a crucial role in transmitting the action potential from the surface of the muscle cell to the interior, which is essential for muscle contraction.
• Myofibrils: These are the basic rod - like units of a muscle cell composed of myofilaments, not the structure formed by sarcolemma extensions.

Answer:

C. transverse tubules (T - tubules)