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Content: It is the segment between 2 successive Z-Lines. What are the T tubules and what is their chief function? - T tubules are transverse tubules formed by inward extensions of the sarcolemma. -Function is to allow electrical impulses traveling along the sarcomere to move deeper into the cell. What do impulses from the T tubules do to the sarcoplasmic reticulum? - It stimulates the membranes forming the sacs of sarcoplasmic reticulum. - This stimulation causes the SR to release its stored calcium ions. What types of protein are found in thick and thin myofilaments? Where is each type of protein found? Thick myofilaments: