Answer
Fig. 11.2
Two transverse tubules (T-tubules) associate closely with each terminal cisternae( on each side) because the electrical stimulation that spreads down the T-tubule needs to excite the opening of calcium gates in the terminal cisternae.
Work Step by Step
Each skeletal muscle cell has many myofibrils ( 11 -100s).The sarcoplasmic reticulum ( SER) of the cell forms a network around each myofibril. Occasionally (periodically), the SR forms dilated sacs ( terminal cisternae) which cross the muscle fiber from one side to the other. Transverse tubules (T-tubules) also develop from SR. They are infoldings of SR which also penetrate muscle cells from side to side. An associated terminal cisternae runs on each side of a T-tubule. This facilitates the spread of neural/ electrical stimulation.
