---Which regions shorten during contraction?
13. The neuron and all the muscle fibers it excites are referred to as a
14. What is meant by "recruitment" with regards to skeletal muscle contraction?
15. The calcium released into the sarcoplasm binds to _______ which causes _______ to shift away from the cross-bridge binding sites on the thin filament.
16. Use the following to fill in the blanks of the sentences below.
myofibrils, transverse tubules, muscle, lateral sacs, muscle fiber, sarcoplasmic reticulum, muscle cell, fascicles
Sarcomeres are collected into long fiber-like processes called _______ or _______ which are then again themselves collected within a multinucleated _______ which are grouped into _______. The myofibrils are surrounded by _______ containing large stores of calcium ions. The Ca$^{2+}$ will be released when the action potential travels along the sarcolemma down through the _______ exciting the _______ of the _______.
17. Describe four actions of ATP in the excitation-contraction coupling in a skeletal muscle fiber.
18. When a muscle fiber is contracting at full force it is called a _______ contra