Which term is used to refer to the involuntary contraction of muscles?

The term that refers to the involuntary contraction of muscles is indeed involuntary contraction. This term signifies muscle contractions that occur without conscious control, such as those seen in smooth muscles within internal organs or cardiac muscles in the heart. Involuntary contractions are essential for various bodily functions, such as digestion and maintaining circulation, as they operate automatically and are controlled by the autonomic nervous system.

In contrast, voluntary contractions are those that are consciously controlled, often in the context of skeletal muscles when we intend to move. Isometric contractions involve muscle tension without a change in muscle length, while eccentric contractions refer to the lengthening of a muscle while it is under tension. Both isometric and eccentric contractions are categorized differently and typically involve conscious control or are part of more complex movements. Understanding these distinctions helps clarify the unique nature of involuntary muscle contractions associated with autonomic functions.