The system of flexing and extending muscles makes movement of appendages easy to understand.But how are some actions possible (sticking out your tongue,beating of your heart)when these structures have no bone structure with opposing flexors and extensors in them?
A)One set of muscle cells must therefore be able to both contract and expand.
B)These structures must be empty chambers,and fluids forced into them expand them.
C)Muscle cells running diagonally or crosswise amidst the longitudinal muscles must contract and force the long relaxed muscle cells to elongate.
D)This cannot be explained at present.

Question

Quizplus · Accepted Answer

Muscle cells running diagonally or crosswise can contract to create movement in structures without bones, like the tongue or heart, by working against the longitudinal muscles.

The System of Flexing and Extending Muscles Makes Movement of Appendages