Which membrane forms the outer boundary of a skeletal muscle fiber and conducts the impulse along its surface?

Which structure stores calcium ions and releases them around the contractile rods after electrical stimulation?

A surface impulse must reach the interior of the fiber quickly. Which tunnel-like membrane passage carries it inward?

Which enlarged sac lies at each side of a T tubule and helps release calcium near a fibril?

Which repeating unit is the contractile unit of a myofibril?

Which long cylindrical organelle fills much of the cell and is built from repeating contractile segments?

Which connective tissue layer wraps each individual skeletal muscle fiber?

Which connective tissue layer surrounds each bundle of skeletal muscle fibers?

Which dense connective tissue sheath surrounds an entire skeletal muscle before smaller fiber bundles are reached?

During contraction, which light region contains only thin filaments and becomes narrower?

Which dark region spans the full length of thick filaments, including the overlap with thin filaments?

At the center of the dark region, which area contains thick filaments but no thin filaments and shrinks during shortening?

Which boundary anchors thin filaments and marks one end of a contractile segment?

Which central line holds thick filaments in alignment halfway between the two boundaries?

As a sarcomere shortens during contraction, which region keeps the same width because the thick filaments do not change length?

Which light region is crossed by a boundary line and contains thin filaments from neighboring contractile units?

Which protein forms the thick filament and has projecting heads that bind and pull on the thin filament?

Which protein forms most of the thin filament and provides sites where thick-filament heads attach?

Which protein complex binds calcium and starts the shift that uncovers attachment sites on the thin filament?

Which long regulatory protein blocks attachment sites on the thin filament until calcium changes its position?

Which filament protein splits ATP during the cross-bridge cycle to power movement?

Which bundle of fibers lies immediately inside the outer sheath of a whole muscle?

After the bundle level in the size sequence, what long multinucleated cell comes next?

In the sequence whole muscle → fiber bundle → muscle fiber → ___ → contractile segment, which level fills the blank?

In the sequence myofibril → contractile unit → ___, what level consists of the actin and myosin strands themselves?