Which of the following is true concerning the anatomy of a skeletal muscle fiber?

a. myofibrils contain thick and thin filaments.
b. the sarcolemma is the muscle fiber’s cytoplasm.
c. t tubules are extensions of the sarcoplasmic reticulum.
d. a triad consists of a t tubule and the nearby sarcolemma.

The correct answer is: A. Myofibrils contain thick and thin filaments.

Skeletal muscle cells are called muscle fibers because of their long and cylindrical shape. The plasma membrane of muscle fibers is sarcolemma, the cytoplasm is sarcoplasm, and the smooth endoplasmic reticulum sarcoplasmic reticulum (SR) Sarcoplasmic reticulum is specialized becaused it is involved in the process of contraction, so it stores, releases, and retrieves calcium ions.  

The functional unit of a skeletal muscle fiber is the sarcomere which consists of highly organized contractile myofilaments actin that are thin filaments and myosin (thick filaments), together with other support proteins.  

where is the scientific experiment?

answer:

convection currents in the magma drive plate tectonics. heat generated from the radioactive decay of elements deep in the interior of the earth creates magma (molten rock) in the aesthenosphere. the aesthenosphere (70 ~ 250 km) is part of the mantle, the middle sphere of the earth that extends to 2900 km.